diff --git a/Documentation/MyFirstObjectWalk.adoc b/Documentation/MyFirstObjectWalk.adoc
index bfe8f5f5611209..b7b2adc5defc0b 100644
--- a/Documentation/MyFirstObjectWalk.adoc
+++ b/Documentation/MyFirstObjectWalk.adoc
@@ -43,7 +43,7 @@ Open up a new file `builtin/walken.c` and set up the command handler:
 #include "builtin.h"
 #include "trace.h"
 
-int cmd_walken(int argc, const char **argv, const char *prefix)
+int cmd_walken(int argc, const char **argv, const char *prefix, struct repository *repo)
 {
 	trace_printf(_("cmd_walken incoming...\n"));
 	return 0;
@@ -86,7 +86,7 @@ int cmd_walken(int argc, const char **argv, const char *prefix)
 Also add the relevant line in `builtin.h` near `cmd_whatchanged()`:
 
 ----
-int cmd_walken(int argc, const char **argv, const char *prefix);
+int cmd_walken(int argc, const char **argv, const char *prefix, struct repository *repo);
 ----
 
 Include the command in `git.c` in `commands[]` near the entry for `whatchanged`,
@@ -96,10 +96,23 @@ maintaining alphabetical ordering:
 { "walken", cmd_walken, RUN_SETUP },
 ----
 
-Add it to the `Makefile` near the line for `builtin/worktree.o`:
+Add an entry for the new command in the both the Make and Meson build system,
+before the entry for `worktree`:
 
+- In the `Makefile`:
 ----
+...
 BUILTIN_OBJS += builtin/walken.o
+...
+----
+
+- In the `meson.build` file:
+----
+builtin_sources = [
+   ...
+  'builtin/walken.c',
+   ...
+]
 ----
 
 Build and test out your command, without forgetting to ensure the `DEVELOPER`
@@ -193,7 +206,7 @@ initialization functions.
 
 Next, we should have a look at any relevant configuration settings (i.e.,
 settings readable and settable from `git config`). This is done by providing a
-callback to `git_config()`; within that callback, you can also invoke methods
+callback to `repo_config()`; within that callback, you can also invoke methods
 from other components you may need that need to intercept these options. Your
 callback will be invoked once per each configuration value which Git knows about
 (global, local, worktree, etc.).
@@ -221,14 +234,14 @@ static int git_walken_config(const char *var, const char *value,
 }
 ----
 
-Make sure to invoke `git_config()` with it in your `cmd_walken()`:
+Make sure to invoke `repo_config()` with it in your `cmd_walken()`:
 
 ----
-int cmd_walken(int argc, const char **argv, const char *prefix)
+int cmd_walken(int argc, const char **argv, const char *prefix, struct repository *repo)
 {
 	...
 
-	git_config(git_walken_config, NULL);
+	repo_config(repo, git_walken_config, NULL);
 
 	...
 }
@@ -250,14 +263,14 @@ We'll also need to include the `revision.h` header:
 
 ...
 
-int cmd_walken(int argc, const char **argv, const char *prefix)
+int cmd_walken(int argc, const char **argv, const char *prefix, struct repository *repo)
 {
 	/* This can go wherever you like in your declarations.*/
 	struct rev_info rev;
 	...
 
-	/* This should go after the git_config() call. */
-	repo_init_revisions(the_repository, &rev, prefix);
+	/* This should go after the repo_config() call. */
+	repo_init_revisions(repo, &rev, prefix);
 
 	...
 }
@@ -305,7 +318,7 @@ Then let's invoke `final_rev_info_setup()` after the call to
 `repo_init_revisions()`:
 
 ----
-int cmd_walken(int argc, const char **argv, const char *prefix)
+int cmd_walken(int argc, const char **argv, const char *prefix, struct repository *repo)
 {
 	...
 
diff --git a/Documentation/RelNotes/2.51.0.adoc b/Documentation/RelNotes/2.51.0.adoc
new file mode 100644
index 00000000000000..478dbd5fb335aa
--- /dev/null
+++ b/Documentation/RelNotes/2.51.0.adoc
@@ -0,0 +1,45 @@
+Git v2.51 Release Notes
+=======================
+
+UI, Workflows & Features
+------------------------
+
+ * Userdiff patterns for the R language have been added.
+
+ * Documentation for "git send-email" has been updated with a bit more
+   credential helper and OAuth information.
+
+ * "git cat-file --batch" learns to understand %(objectmode) atom to
+   allow the caller to tell missing objects (due to repository
+   corruption) and submodules (whose commit objects are OK to be
+   missing) apart.
+
+ * "git diff --no-index dirA dirB" can limit the comparison with
+   pathspec at the end of the command line, just like normal "git
+   diff".
+
+
+Performance, Internal Implementation, Development Support etc.
+--------------------------------------------------------------
+
+ * "git pack-objects" learned to find delta bases from blobs at the
+   same path, using the --path-walk API.
+
+
+Fixes since v2.50
+-----------------
+
+ * A memory-leak in an error code path has been plugged.
+   (merge 7082da85cb ly/commit-graph-graph-write-leakfix later to maint).
+
+ * A memory-leak in an error code path has been plugged.
+   (merge aedebdb6b9 ly/fetch-pack-leakfix later to maint).
+
+ * Meson-based build/test framework now understands TAP output
+   generated by our tests.
+   (merge c1bc974923 ps/meson-tap-parse later to maint).
+
+ * Other code cleanup, docfix, build fix, etc.
+   (merge b257adb571 lo/my-first-ow-doc-update later to maint).
+   (merge 8b34b6a220 ly/sequencer-update-squash-is-fixup-only later to maint).
+   (merge 5dceb8bd05 ly/do-not-localize-bug-messages later to maint).
diff --git a/Documentation/config/feature.adoc b/Documentation/config/feature.adoc
index f061b64b748449..cb49ff2604a632 100644
--- a/Documentation/config/feature.adoc
+++ b/Documentation/config/feature.adoc
@@ -20,6 +20,10 @@ walking fewer objects.
 +
 * `pack.allowPackReuse=multi` may improve the time it takes to create a pack by
 reusing objects from multiple packs instead of just one.
++
+* `pack.usePathWalk` may speed up packfile creation and make the packfiles be
+significantly smaller in the presence of certain filename collisions with Git's
+default name-hash.
 
 feature.manyFiles::
 	Enable config options that optimize for repos with many files in the
diff --git a/Documentation/config/pack.adoc b/Documentation/config/pack.adoc
index da527377fafcb6..75402d5579d4b2 100644
--- a/Documentation/config/pack.adoc
+++ b/Documentation/config/pack.adoc
@@ -155,6 +155,10 @@ pack.useSparse::
 	commits contain certain types of direct renames. Default is
 	`true`.
 
+pack.usePathWalk::
+	Enable the `--path-walk` option by default for `git pack-objects`
+	processes. See linkgit:git-pack-objects[1] for full details.
+
 pack.preferBitmapTips::
 	When selecting which commits will receive bitmaps, prefer a
 	commit at the tip of any reference that is a suffix of any value
diff --git a/Documentation/config/sendemail.adoc b/Documentation/config/sendemail.adoc
index 5ffcfc9f2a76f7..54f1248e647273 100644
--- a/Documentation/config/sendemail.adoc
+++ b/Documentation/config/sendemail.adoc
@@ -1,32 +1,32 @@
 sendemail.identity::
 	A configuration identity. When given, causes values in the
-	'sendemail.<identity>' subsection to take precedence over
-	values in the 'sendemail' section. The default identity is
+	`sendemail.<identity>` subsection to take precedence over
+	values in the `sendemail` section. The default identity is
 	the value of `sendemail.identity`.
 
 sendemail.smtpEncryption::
 	See linkgit:git-send-email[1] for description.  Note that this
-	setting is not subject to the 'identity' mechanism.
+	setting is not subject to the `identity` mechanism.
 
 sendemail.smtpSSLCertPath::
 	Path to ca-certificates (either a directory or a single file).
 	Set it to an empty string to disable certificate verification.
 
 sendemail.<identity>.*::
-	Identity-specific versions of the 'sendemail.*' parameters
+	Identity-specific versions of the `sendemail.*` parameters
 	found below, taking precedence over those when this
 	identity is selected, through either the command-line or
 	`sendemail.identity`.
 
 sendemail.multiEdit::
-	If true (default), a single editor instance will be spawned to edit
+	If `true` (default), a single editor instance will be spawned to edit
 	files you have to edit (patches when `--annotate` is used, and the
-	summary when `--compose` is used). If false, files will be edited one
+	summary when `--compose` is used). If `false`, files will be edited one
 	after the other, spawning a new editor each time.
 
 sendemail.confirm::
 	Sets the default for whether to confirm before sending. Must be
-	one of 'always', 'never', 'cc', 'compose', or 'auto'. See `--confirm`
+	one of `always`, `never`, `cc`, `compose`, or `auto`. See `--confirm`
 	in the linkgit:git-send-email[1] documentation for the meaning of these
 	values.
 
@@ -51,7 +51,7 @@ sendemail.aliasesFile::
 
 sendemail.aliasFileType::
 	Format of the file(s) specified in sendemail.aliasesFile. Must be
-	one of 'mutt', 'mailrc', 'pine', 'elm', 'gnus', or 'sendmail'.
+	one of `mutt`, `mailrc`, `pine`, `elm`, `gnus`, or `sendmail`.
 +
 What an alias file in each format looks like can be found in
 the documentation of the email program of the same name. The
@@ -101,7 +101,7 @@ sendemail.signedOffCc (deprecated)::
 
 sendemail.smtpBatchSize::
 	Number of messages to be sent per connection, after that a relogin
-	will happen.  If the value is 0 or undefined, send all messages in
+	will happen.  If the value is `0` or undefined, send all messages in
 	one connection.
 	See also the `--batch-size` option of linkgit:git-send-email[1].
 
@@ -111,5 +111,5 @@ sendemail.smtpReloginDelay::
 
 sendemail.forbidSendmailVariables::
 	To avoid common misconfiguration mistakes, linkgit:git-send-email[1]
-	will abort with a warning if any configuration options for "sendmail"
+	will abort with a warning if any configuration options for `sendmail`
 	exist. Set this variable to bypass the check.
diff --git a/Documentation/git-cat-file.adoc b/Documentation/git-cat-file.adoc
index cde79ad242bb77..180d1ad363fdf8 100644
--- a/Documentation/git-cat-file.adoc
+++ b/Documentation/git-cat-file.adoc
@@ -307,6 +307,11 @@ newline. The available atoms are:
 `objecttype`::
 	The type of the object (the same as `cat-file -t` reports).
 
+`objectmode`::
+	If the specified object has mode information (such as a tree or
+	index entry), the mode expressed as an octal integer. Otherwise,
+	empty string.
+
 `objectsize`::
 	The size, in bytes, of the object (the same as `cat-file -s`
 	reports).
@@ -368,6 +373,14 @@ If a name is specified that might refer to more than one object (an ambiguous sh
 <object> SP ambiguous LF
 ------------
 
+If a name is specified that refers to a submodule entry in a tree and the
+target object does not exist in the repository, then `cat-file` will ignore
+any custom format and print (with the object ID of the submodule):
+
+------------
+<oid> SP submodule LF
+------------
+
 If `--follow-symlinks` is used, and a symlink in the repository points
 outside the repository, then `cat-file` will ignore any custom format
 and print:
diff --git a/Documentation/git-diff.adoc b/Documentation/git-diff.adoc
index dec173a345179e..272331afbaec73 100644
--- a/Documentation/git-diff.adoc
+++ b/Documentation/git-diff.adoc
@@ -14,7 +14,7 @@ git diff [<options>] --cached [--merge-base] [<commit>] [--] [<path>...]
 git diff [<options>] [--merge-base] <commit> [<commit>...] <commit> [--] [<path>...]
 git diff [<options>] <commit>...<commit> [--] [<path>...]
 git diff [<options>] <blob> <blob>
-git diff [<options>] --no-index [--] <path> <path>
+git diff [<options>] --no-index [--] <path> <path> [<pathspec>...]
 
 DESCRIPTION
 -----------
@@ -31,14 +31,18 @@ files on disk.
 	further add to the index but you still haven't.  You can
 	stage these changes by using linkgit:git-add[1].
 
-`git diff [<options>] --no-index [--] <path> <path>`::
+`git diff [<options>] --no-index [--] <path> <path> [<pathspec>...]`::
 
 	This form is to compare the given two paths on the
 	filesystem.  You can omit the `--no-index` option when
 	running the command in a working tree controlled by Git and
 	at least one of the paths points outside the working tree,
 	or when running the command outside a working tree
-	controlled by Git. This form implies `--exit-code`.
+	controlled by Git. This form implies `--exit-code`. If both
+	paths point to directories, additional pathspecs may be
+	provided. These will limit the files included in the
+	difference. All such pathspecs must be relative as they
+	apply to both sides of the diff.
 
 `git diff [<options>] --cached [--merge-base] [<commit>] [--] [<path>...]`::
 
diff --git a/Documentation/git-pack-objects.adoc b/Documentation/git-pack-objects.adoc
index 7f69ae4855f6ce..b1c5aa27da4d55 100644
--- a/Documentation/git-pack-objects.adoc
+++ b/Documentation/git-pack-objects.adoc
@@ -10,13 +10,13 @@ SYNOPSIS
 --------
 [verse]
 'git pack-objects' [-q | --progress | --all-progress] [--all-progress-implied]
-	[--no-reuse-delta] [--delta-base-offset] [--non-empty]
-	[--local] [--incremental] [--window=<n>] [--depth=<n>]
-	[--revs [--unpacked | --all]] [--keep-pack=<pack-name>]
-	[--cruft] [--cruft-expiration=<time>]
-	[--stdout [--filter=<filter-spec>] | <base-name>]
-	[--shallow] [--keep-true-parents] [--[no-]sparse]
-	[--name-hash-version=<n>] < <object-list>
+		   [--no-reuse-delta] [--delta-base-offset] [--non-empty]
+		   [--local] [--incremental] [--window=<n>] [--depth=<n>]
+		   [--revs [--unpacked | --all]] [--keep-pack=<pack-name>]
+		   [--cruft] [--cruft-expiration=<time>]
+		   [--stdout [--filter=<filter-spec>] | <base-name>]
+		   [--shallow] [--keep-true-parents] [--[no-]sparse]
+		   [--name-hash-version=<n>] [--path-walk] < <object-list>
 
 
 DESCRIPTION
@@ -375,6 +375,17 @@ many different directories. At the moment, this version is not allowed
 when writing reachability bitmap files with `--write-bitmap-index` and it
 will be automatically changed to version `1`.
 
+--path-walk::
+	Perform compression by first organizing objects by path, then a
+	second pass that compresses across paths as normal. This has the
+	potential to improve delta compression especially in the presence
+	of filenames that cause collisions in Git's default name-hash
+	algorithm.
++
+Incompatible with `--delta-islands`, `--shallow`, or `--filter`. The
+`--use-bitmap-index` option will be ignored in the presence of
+`--path-walk.`
+
 
 DELTA ISLANDS
 -------------
diff --git a/Documentation/git-repack.adoc b/Documentation/git-repack.adoc
index e1cd75eebe0afe..d12c4985f61c06 100644
--- a/Documentation/git-repack.adoc
+++ b/Documentation/git-repack.adoc
@@ -11,7 +11,7 @@ SYNOPSIS
 [verse]
 'git repack' [-a] [-A] [-d] [-f] [-F] [-l] [-n] [-q] [-b] [-m]
 	[--window=<n>] [--depth=<n>] [--threads=<n>] [--keep-pack=<pack-name>]
-	[--write-midx] [--name-hash-version=<n>]
+	[--write-midx] [--name-hash-version=<n>] [--path-walk]
 
 DESCRIPTION
 -----------
@@ -258,6 +258,9 @@ linkgit:git-multi-pack-index[1]).
 	Provide this argument to the underlying `git pack-objects` process.
 	See linkgit:git-pack-objects[1] for full details.
 
+--path-walk::
+	Pass the `--path-walk` option to the underlying `git pack-objects`
+	process. See linkgit:git-pack-objects[1] for full details.
 
 CONFIGURATION
 -------------
diff --git a/Documentation/git-send-email.adoc b/Documentation/git-send-email.adoc
index 26fda63c2fc1ff..7bd09c254b271e 100644
--- a/Documentation/git-send-email.adoc
+++ b/Documentation/git-send-email.adoc
@@ -21,7 +21,7 @@ Takes the patches given on the command line and emails them out.
 Patches can be specified as files, directories (which will send all
 files in the directory), or directly as a revision list.  In the
 last case, any format accepted by linkgit:git-format-patch[1] can
-be passed to git send-email, as well as options understood by
+be passed to `git send-email`, as well as options understood by
 linkgit:git-format-patch[1].
 
 The header of the email is configurable via command-line options.  If not
@@ -35,11 +35,11 @@ There are two formats accepted for patch files:
 This is what linkgit:git-format-patch[1] generates.  Most headers and MIME
 formatting are ignored.
 
-2. The original format used by Greg Kroah-Hartman's 'send_lots_of_email.pl'
+2. The original format used by Greg Kroah-Hartman's `send_lots_of_email.pl`
    script
 +
-This format expects the first line of the file to contain the "Cc:" value
-and the "Subject:" of the message as the second line.
+This format expects the first line of the file to contain the `Cc:` value
+and the `Subject:` of the message as the second line.
 
 
 OPTIONS
@@ -54,13 +54,13 @@ Composing
 	`sendemail.multiEdit`.
 
 --bcc=<address>,...::
-	Specify a "Bcc:" value for each email. Default is the value of
+	Specify a `Bcc:` value for each email. Default is the value of
 	`sendemail.bcc`.
 +
 This option may be specified multiple times.
 
 --cc=<address>,...::
-	Specify a starting "Cc:" value for each email.
+	Specify a starting `Cc:` value for each email.
 	Default is the value of `sendemail.cc`.
 +
 This option may be specified multiple times.
@@ -69,14 +69,14 @@ This option may be specified multiple times.
 	Invoke a text editor (see GIT_EDITOR in linkgit:git-var[1])
 	to edit an introductory message for the patch series.
 +
-When `--compose` is used, git send-email will use the From, To, Cc, Bcc,
-Subject, Reply-To, and In-Reply-To headers specified in the message. If
-the body of the message (what you type after the headers and a blank
-line) only contains blank (or Git: prefixed) lines, the summary won't be
+When `--compose` is used, `git send-email` will use the `From`, `To`, `Cc`,
+`Bcc`, `Subject`, `Reply-To`, and `In-Reply-To` headers specified in the
+message. If the body of the message (what you type after the headers and a
+blank line) only contains blank (or `Git:` prefixed) lines, the summary won't be
 sent, but the headers mentioned above will be used unless they are
 removed.
 +
-Missing From or In-Reply-To headers will be prompted for.
+Missing `From` or `In-Reply-To` headers will be prompted for.
 +
 See the CONFIGURATION section for `sendemail.multiEdit`.
 
@@ -85,13 +85,13 @@ See the CONFIGURATION section for `sendemail.multiEdit`.
 	the value of the `sendemail.from` configuration option is used.  If
 	neither the command-line option nor `sendemail.from` are set, then the
 	user will be prompted for the value.  The default for the prompt will be
-	the value of GIT_AUTHOR_IDENT, or GIT_COMMITTER_IDENT if that is not
-	set, as returned by "git var -l".
+	the value of `GIT_AUTHOR_IDENT`, or `GIT_COMMITTER_IDENT` if that is not
+	set, as returned by `git var -l`.
 
 --reply-to=<address>::
 	Specify the address where replies from recipients should go to.
 	Use this if replies to messages should go to another address than what
-	is specified with the --from parameter.
+	is specified with the `--from` parameter.
 
 --in-reply-to=<identifier>::
 	Make the first mail (or all the mails with `--no-thread`) appear as a
@@ -112,14 +112,14 @@ illustration below where `[PATCH v2 0/3]` is in reply to `[PATCH 0/2]`:
       [PATCH v2 2/3] New tests
       [PATCH v2 3/3] Implementation
 +
-Only necessary if --compose is also set.  If --compose
+Only necessary if `--compose` is also set.  If `--compose`
 is not set, this will be prompted for.
 
 --[no-]outlook-id-fix::
 	Microsoft Outlook SMTP servers discard the Message-ID sent via email and
 	assign a new random Message-ID, thus breaking threads.
 +
-With `--outlook-id-fix`, 'git send-email' uses a mechanism specific to
+With `--outlook-id-fix`, `git send-email` uses a mechanism specific to
 Outlook servers to learn the Message-ID the server assigned to fix the
 threading. Use it only when you know that the server reports the
 rewritten Message-ID the same way as Outlook servers do.
@@ -130,14 +130,14 @@ to 'smtp.office365.com' or 'smtp-mail.outlook.com'. Use
 
 --subject=<string>::
 	Specify the initial subject of the email thread.
-	Only necessary if --compose is also set.  If --compose
+	Only necessary if `--compose` is also set.  If `--compose`
 	is not set, this will be prompted for.
 
 --to=<address>,...::
 	Specify the primary recipient of the emails generated. Generally, this
 	will be the upstream maintainer of the project involved. Default is the
 	value of the `sendemail.to` configuration value; if that is unspecified,
-	and --to-cmd is not specified, this will be prompted for.
+	and `--to-cmd` is not specified, this will be prompted for.
 +
 This option may be specified multiple times.
 
@@ -145,30 +145,30 @@ This option may be specified multiple times.
 	When encountering a non-ASCII message or subject that does not
 	declare its encoding, add headers/quoting to indicate it is
 	encoded in <encoding>.  Default is the value of the
-	'sendemail.assume8bitEncoding'; if that is unspecified, this
+	`sendemail.assume8bitEncoding`; if that is unspecified, this
 	will be prompted for if any non-ASCII files are encountered.
 +
 Note that no attempts whatsoever are made to validate the encoding.
 
 --compose-encoding=<encoding>::
 	Specify encoding of compose message. Default is the value of the
-	'sendemail.composeEncoding'; if that is unspecified, UTF-8 is assumed.
+	`sendemail.composeEncoding`; if that is unspecified, UTF-8 is assumed.
 
 --transfer-encoding=(7bit|8bit|quoted-printable|base64|auto)::
 	Specify the transfer encoding to be used to send the message over SMTP.
-	7bit will fail upon encountering a non-ASCII message.  quoted-printable
+	`7bit` will fail upon encountering a non-ASCII message. `quoted-printable`
 	can be useful when the repository contains files that contain carriage
-	returns, but makes the raw patch email file (as saved from a MUA) much
-	harder to inspect manually.  base64 is even more fool proof, but also
-	even more opaque.  auto will use 8bit when possible, and quoted-printable
-	otherwise.
+	returns, but makes the raw patch email file (as saved from an MUA) much
+	harder to inspect manually. `base64` is even more fool proof, but also
+	even more opaque. `auto` will use `8bit` when possible, and
+	`quoted-printable` otherwise.
 +
 Default is the value of the `sendemail.transferEncoding` configuration
 value; if that is unspecified, default to `auto`.
 
 --xmailer::
 --no-xmailer::
-	Add (or prevent adding) the "X-Mailer:" header.  By default,
+	Add (or prevent adding) the `X-Mailer:` header.  By default,
 	the header is added, but it can be turned off by setting the
 	`sendemail.xmailer` configuration variable to `false`.
 
@@ -178,9 +178,9 @@ Sending
 --envelope-sender=<address>::
 	Specify the envelope sender used to send the emails.
 	This is useful if your default address is not the address that is
-	subscribed to a list. In order to use the 'From' address, set the
-	value to "auto". If you use the sendmail binary, you must have
-	suitable privileges for the -f parameter.  Default is the value of the
+	subscribed to a list. In order to use the `From` address, set the
+	value to `auto`. If you use the `sendmail` binary, you must have
+	suitable privileges for the `-f` parameter.  Default is the value of the
 	`sendemail.envelopeSender` configuration variable; if that is
 	unspecified, choosing the envelope sender is left to your MTA.
 
@@ -189,27 +189,27 @@ Sending
 	be sendmail-like; specifically, it must support the `-i` option.
 	The command will be executed in the shell if necessary.  Default
 	is the value of `sendemail.sendmailCmd`.  If unspecified, and if
-	--smtp-server is also unspecified, git-send-email will search
-	for `sendmail` in `/usr/sbin`, `/usr/lib` and $PATH.
+	`--smtp-server` is also unspecified, `git send-email` will search
+	for `sendmail` in `/usr/sbin`, `/usr/lib` and `$PATH`.
 
 --smtp-encryption=<encryption>::
 	Specify in what way encrypting begins for the SMTP connection.
-	Valid values are 'ssl' and 'tls'. Any other value reverts to plain
+	Valid values are `ssl` and `tls`. Any other value reverts to plain
 	(unencrypted) SMTP, which defaults to port 25.
 	Despite the names, both values will use the same newer version of TLS,
-	but for historic reasons have these names. 'ssl' refers to "implicit"
+	but for historic reasons have these names. `ssl` refers to "implicit"
 	encryption (sometimes called SMTPS), that uses port 465 by default.
-	'tls' refers to "explicit" encryption (often known as STARTTLS),
+	`tls` refers to "explicit" encryption (often known as STARTTLS),
 	that uses port 25 by default. Other ports might be used by the SMTP
 	server, which are not the default. Commonly found alternative port for
-	'tls' and unencrypted is 587. You need to check your provider's
+	`tls` and unencrypted is 587. You need to check your provider's
 	documentation or your server configuration to make sure
 	for your own case. Default is the value of `sendemail.smtpEncryption`.
 
 --smtp-domain=<FQDN>::
 	Specifies the Fully Qualified Domain Name (FQDN) used in the
 	HELO/EHLO command to the SMTP server.  Some servers require the
-	FQDN to match your IP address.  If not set, git send-email attempts
+	FQDN to match your IP address.  If not set, `git send-email` attempts
 	to determine your FQDN automatically.  Default is the value of
 	`sendemail.smtpDomain`.
 
@@ -223,10 +223,10 @@ $ git send-email --smtp-auth="PLAIN LOGIN GSSAPI" ...
 +
 If at least one of the specified mechanisms matches the ones advertised by the
 SMTP server and if it is supported by the utilized SASL library, the mechanism
-is used for authentication. If neither 'sendemail.smtpAuth' nor `--smtp-auth`
+is used for authentication. If neither `sendemail.smtpAuth` nor `--smtp-auth`
 is specified, all mechanisms supported by the SASL library can be used. The
-special value 'none' maybe specified to completely disable authentication
-independently of `--smtp-user`
+special value `none` maybe specified to completely disable authentication
+independently of `--smtp-user`.
 
 --smtp-pass[=<password>]::
 	Password for SMTP-AUTH. The argument is optional: If no
@@ -238,16 +238,16 @@ Furthermore, passwords need not be specified in configuration files
 or on the command line. If a username has been specified (with
 `--smtp-user` or a `sendemail.smtpUser`), but no password has been
 specified (with `--smtp-pass` or `sendemail.smtpPass`), then
-a password is obtained using 'git-credential'.
+a password is obtained using linkgit:git-credential[1].
 
 --no-smtp-auth::
-	Disable SMTP authentication. Short hand for `--smtp-auth=none`
+	Disable SMTP authentication. Short hand for `--smtp-auth=none`.
 
 --smtp-server=<host>::
 	If set, specifies the outgoing SMTP server to use (e.g.
 	`smtp.example.com` or a raw IP address).  If unspecified, and if
 	`--sendmail-cmd` is also unspecified, the default is to search
-	for `sendmail` in `/usr/sbin`, `/usr/lib` and $PATH if such a
+	for `sendmail` in `/usr/sbin`, `/usr/lib` and `$PATH` if such a
 	program is available, falling back to `localhost` otherwise.
 +
 For backward compatibility, this option can also specify a full pathname
@@ -260,7 +260,7 @@ instead.
 	Specifies a port different from the default port (SMTP
 	servers typically listen to smtp port 25, but may also listen to
 	submission port 587, or the common SSL smtp port 465);
-	symbolic port names (e.g. "submission" instead of 587)
+	symbolic port names (e.g. `submission` instead of 587)
 	are also accepted. The port can also be set with the
 	`sendemail.smtpServerPort` configuration variable.
 
@@ -269,17 +269,17 @@ instead.
 	Default value can be specified by the `sendemail.smtpServerOption`
 	configuration option.
 +
-The --smtp-server-option option must be repeated for each option you want
+The `--smtp-server-option` option must be repeated for each option you want
 to pass to the server. Likewise, different lines in the configuration files
 must be used for each option.
 
 --smtp-ssl::
-	Legacy alias for '--smtp-encryption ssl'.
+	Legacy alias for `--smtp-encryption ssl`.
 
 --smtp-ssl-cert-path::
 	Path to a store of trusted CA certificates for SMTP SSL/TLS
 	certificate validation (either a directory that has been processed
-	by 'c_rehash', or a single file containing one or more PEM format
+	by `c_rehash`, or a single file containing one or more PEM format
 	certificates concatenated together: see verify(1) -CAfile and
 	-CApath for more information on these). Set it to an empty string
 	to disable certificate verification. Defaults to the value of the
@@ -298,18 +298,18 @@ must be used for each option.
 	connection and authentication problems.
 
 --batch-size=<num>::
-	Some email servers (e.g. smtp.163.com) limit the number emails to be
+	Some email servers (e.g. 'smtp.163.com') limit the number of emails to be
 	sent per session (connection) and this will lead to a failure when
 	sending many messages.  With this option, send-email will disconnect after
-	sending $<num> messages and wait for a few seconds (see --relogin-delay)
-	and reconnect, to work around such a limit.  You may want to
-	use some form of credential helper to avoid having to retype
-	your password every time this happens.  Defaults to the
+	sending _<num>_ messages and wait for a few seconds
+	(see `--relogin-delay`) and reconnect, to work around such a limit.
+	You may want to use some form of credential helper to avoid having to
+	retype your password every time this happens.  Defaults to the
 	`sendemail.smtpBatchSize` configuration variable.
 
 --relogin-delay=<int>::
-	Waiting $<int> seconds before reconnecting to SMTP server. Used together
-	with --batch-size option.  Defaults to the `sendemail.smtpReloginDelay`
+	Waiting _<int>_ seconds before reconnecting to SMTP server. Used together
+	with `--batch-size` option.  Defaults to the `sendemail.smtpReloginDelay`
 	configuration variable.
 
 Automating
@@ -318,7 +318,7 @@ Automating
 --no-to::
 --no-cc::
 --no-bcc::
-	Clears any list of "To:", "Cc:", "Bcc:" addresses previously
+	Clears any list of `To:`, `Cc:`, `Bcc:` addresses previously
 	set via config.
 
 --no-identity::
@@ -327,13 +327,13 @@ Automating
 
 --to-cmd=<command>::
 	Specify a command to execute once per patch file which
-	should generate patch file specific "To:" entries.
+	should generate patch file specific `To:` entries.
 	Output of this command must be single email address per line.
-	Default is the value of 'sendemail.toCmd' configuration value.
+	Default is the value of `sendemail.toCmd` configuration value.
 
 --cc-cmd=<command>::
 	Specify a command to execute once per patch file which
-	should generate patch file specific "Cc:" entries.
+	should generate patch file specific `Cc:` entries.
 	Output of this command must be single email address per line.
 	Default is the value of `sendemail.ccCmd` configuration value.
 
@@ -341,7 +341,7 @@ Automating
 	Specify a command that is executed once per outgoing message
 	and output RFC 2822 style header lines to be inserted into
 	them. When the `sendemail.headerCmd` configuration variable is
-	set, its value is always used. When --header-cmd is provided
+	set, its value is always used. When `--header-cmd` is provided
 	at the command line, its value takes precedence over the
 	`sendemail.headerCmd` configuration variable.
 
@@ -350,7 +350,7 @@ Automating
 
 --[no-]chain-reply-to::
 	If this is set, each email will be sent as a reply to the previous
-	email sent.  If disabled with "--no-chain-reply-to", all emails after
+	email sent.  If disabled with `--no-chain-reply-to`, all emails after
 	the first will be sent as replies to the first email sent.  When using
 	this, it is recommended that the first file given be an overview of the
 	entire patch series. Disabled by default, but the `sendemail.chainReplyTo`
@@ -358,79 +358,80 @@ Automating
 
 --identity=<identity>::
 	A configuration identity. When given, causes values in the
-	'sendemail.<identity>' subsection to take precedence over
-	values in the 'sendemail' section. The default identity is
+	`sendemail.<identity>` subsection to take precedence over
+	values in the `sendemail` section. The default identity is
 	the value of `sendemail.identity`.
 
 --[no-]signed-off-by-cc::
-	If this is set, add emails found in the `Signed-off-by` trailer or Cc: lines to the
-	cc list. Default is the value of `sendemail.signedOffByCc` configuration
-	value; if that is unspecified, default to --signed-off-by-cc.
+	If this is set, add emails found in the `Signed-off-by` trailer or `Cc:`
+	lines to the cc list. Default is the value of `sendemail.signedOffByCc`
+	configuration value; if that is unspecified, default to
+	`--signed-off-by-cc`.
 
 --[no-]cc-cover::
-	If this is set, emails found in Cc: headers in the first patch of
+	If this is set, emails found in `Cc:` headers in the first patch of
 	the series (typically the cover letter) are added to the cc list
-	for each email set. Default is the value of 'sendemail.ccCover'
-	configuration value; if that is unspecified, default to --no-cc-cover.
+	for each email set. Default is the value of `sendemail.ccCover`
+	configuration value; if that is unspecified, default to `--no-cc-cover`.
 
 --[no-]to-cover::
-	If this is set, emails found in To: headers in the first patch of
+	If this is set, emails found in `To:` headers in the first patch of
 	the series (typically the cover letter) are added to the to list
-	for each email set. Default is the value of 'sendemail.toCover'
-	configuration value; if that is unspecified, default to --no-to-cover.
+	for each email set. Default is the value of `sendemail.toCover`
+	configuration value; if that is unspecified, default to `--no-to-cover`.
 
 --suppress-cc=<category>::
 	Specify an additional category of recipients to suppress the
 	auto-cc of:
 +
 --
-- 'author' will avoid including the patch author.
-- 'self' will avoid including the sender.
-- 'cc' will avoid including anyone mentioned in Cc lines in the patch header
-  except for self (use 'self' for that).
-- 'bodycc' will avoid including anyone mentioned in Cc lines in the
-  patch body (commit message) except for self (use 'self' for that).
-- 'sob' will avoid including anyone mentioned in the Signed-off-by trailers except
-  for self (use 'self' for that).
-- 'misc-by' will avoid including anyone mentioned in Acked-by,
+- `author` will avoid including the patch author.
+- `self` will avoid including the sender.
+- `cc` will avoid including anyone mentioned in Cc lines in the patch header
+  except for self (use `self` for that).
+- `bodycc` will avoid including anyone mentioned in Cc lines in the
+  patch body (commit message) except for self (use `self` for that).
+- `sob` will avoid including anyone mentioned in the Signed-off-by trailers except
+  for self (use `self` for that).
+- `misc-by` will avoid including anyone mentioned in Acked-by,
   Reviewed-by, Tested-by and other "-by" lines in the patch body,
-  except Signed-off-by (use 'sob' for that).
-- 'cccmd' will avoid running the --cc-cmd.
-- 'body' is equivalent to 'sob' + 'bodycc' + 'misc-by'.
-- 'all' will suppress all auto cc values.
+  except Signed-off-by (use `sob` for that).
+- `cccmd` will avoid running the --cc-cmd.
+- `body` is equivalent to `sob` + `bodycc` + `misc-by`.
+- `all` will suppress all auto cc values.
 --
 +
 Default is the value of `sendemail.suppressCc` configuration value; if
-that is unspecified, default to 'self' if --suppress-from is
-specified, as well as 'body' if --no-signed-off-cc is specified.
+that is unspecified, default to `self` if `--suppress-from` is
+specified, as well as `body` if `--no-signed-off-cc` is specified.
 
 --[no-]suppress-from::
-	If this is set, do not add the From: address to the cc: list.
+	If this is set, do not add the `From:` address to the `Cc:` list.
 	Default is the value of `sendemail.suppressFrom` configuration
-	value; if that is unspecified, default to --no-suppress-from.
+	value; if that is unspecified, default to `--no-suppress-from`.
 
 --[no-]thread::
-	If this is set, the In-Reply-To and References headers will be
+	If this is set, the `In-Reply-To` and `References` headers will be
 	added to each email sent.  Whether each mail refers to the
-	previous email (`deep` threading per 'git format-patch'
+	previous email (`deep` threading per `git format-patch`
 	wording) or to the first email (`shallow` threading) is
-	governed by "--[no-]chain-reply-to".
+	governed by `--[no-]chain-reply-to`.
 +
-If disabled with "--no-thread", those headers will not be added
-(unless specified with --in-reply-to).  Default is the value of the
+If disabled with `--no-thread`, those headers will not be added
+(unless specified with `--in-reply-to`).  Default is the value of the
 `sendemail.thread` configuration value; if that is unspecified,
-default to --thread.
+default to `--thread`.
 +
 It is up to the user to ensure that no In-Reply-To header already
-exists when 'git send-email' is asked to add it (especially note that
-'git format-patch' can be configured to do the threading itself).
+exists when `git send-email` is asked to add it (especially note that
+`git format-patch` can be configured to do the threading itself).
 Failure to do so may not produce the expected result in the
 recipient's MUA.
 
 --[no-]mailmap::
 	Use the mailmap file (see linkgit:gitmailmap[5]) to map all
 	addresses to their canonical real name and email address. Additional
-	mailmap data specific to git-send-email may be provided using the
+	mailmap data specific to `git send-email` may be provided using the
 	`sendemail.mailmap.file` or `sendemail.mailmap.blob` configuration
 	values. Defaults to `sendemail.mailmap`.
 
@@ -441,17 +442,17 @@ Administering
 	Confirm just before sending:
 +
 --
-- 'always' will always confirm before sending
-- 'never' will never confirm before sending
-- 'cc' will confirm before sending when send-email has automatically
-  added addresses from the patch to the Cc list
-- 'compose' will confirm before sending the first message when using --compose.
-- 'auto' is equivalent to 'cc' + 'compose'
+- `always` will always confirm before sending.
+- `never` will never confirm before sending.
+- `cc` will confirm before sending when send-email has automatically
+  added addresses from the patch to the Cc list.
+- `compose` will confirm before sending the first message when using --compose.
+- `auto` is equivalent to `cc` + `compose`.
 --
 +
 Default is the value of `sendemail.confirm` configuration value; if that
-is unspecified, default to 'auto' unless any of the suppress options
-have been specified, in which case default to 'compose'.
+is unspecified, default to `auto` unless any of the suppress options
+have been specified, in which case default to `compose`.
 
 --dry-run::
 	Do everything except actually send the emails.
@@ -460,10 +461,10 @@ have been specified, in which case default to 'compose'.
 	When an argument may be understood either as a reference or as a file name,
 	choose to understand it as a format-patch argument (`--format-patch`)
 	or as a file name (`--no-format-patch`). By default, when such a conflict
-	occurs, git send-email will fail.
+	occurs, `git send-email` will fail.
 
 --quiet::
-	Make git-send-email less verbose.  One line per email should be
+	Make `git send-email` less verbose.  One line per email should be
 	all that is output.
 
 --[no-]validate::
@@ -474,7 +475,7 @@ have been specified, in which case default to 'compose'.
 		*	Invoke the sendemail-validate hook if present (see linkgit:githooks[5]).
 		*	Warn of patches that contain lines longer than
 			998 characters unless a suitable transfer encoding
-			('auto', 'base64', or 'quoted-printable') is used;
+			(`auto`, `base64`, or `quoted-printable`) is used;
 			this is due to SMTP limits as described by
 			https://www.ietf.org/rfc/rfc5322.txt.
 --
@@ -493,13 +494,13 @@ Information
 	Instead of the normal operation, dump the shorthand alias names from
 	the configured alias file(s), one per line in alphabetical order. Note
 	that this only includes the alias name and not its expanded email addresses.
-	See 'sendemail.aliasesFile' for more information about aliases.
+	See `sendemail.aliasesFile` for more information about aliases.
 
 --translate-aliases::
 	Instead of the normal operation, read from standard input and
 	interpret each line as an email alias. Translate it according to the
 	configured alias file(s). Output each translated name and email
-	address to standard output, one per line. See 'sendemail.aliasFile'
+	address to standard output, one per line. See `sendemail.aliasFile`
 	for more information about aliases.
 
 CONFIGURATION
@@ -524,15 +525,18 @@ edit `~/.gitconfig` to specify your account settings:
 	smtpServerPort = 587
 ----
 
+Gmail does not allow using your regular password for `git send-email`.
 If you have multi-factor authentication set up on your Gmail account, you can
-generate an app-specific password for use with 'git send-email'. Visit
+generate an app-specific password for use with `git send-email`. Visit
 https://security.google.com/settings/security/apppasswords to create it.
 
-You can also use OAuth2.0 authentication with Gmail. `OAUTHBEARER` and
-`XOAUTH2` are common methods used for this type of authentication. Gmail
-supports both of them. As an example, if you want to use `OAUTHBEARER`, edit
-your `~/.gitconfig` file and add `smtpAuth = OAUTHBEARER` to your account
-settings:
+Alternatively, instead of using an app-specific password, you can use
+OAuth2.0 authentication with Gmail. OAuth2.0 is more secure than
+app-specific passwords, and works regardless of whether you have multi-factor
+authentication set up. `OAUTHBEARER` and `XOAUTH2` are common mechanisms used
+for this type of authentication. Gmail supports both of them. As an example,
+if you want to use `OAUTHBEARER`, edit your `~/.gitconfig` file and add
+`smtpAuth = OAUTHBEARER` to your account settings:
 
 ----
 [sendemail]
@@ -543,11 +547,15 @@ settings:
 	smtpAuth = OAUTHBEARER
 ----
 
+Another alternative is using a tool developed by Google known as
+https://github.com/google/gmail-oauth2-tools/tree/master/go/sendgmail[sendgmail]
+to send emails using `git send-email`.
+
 Use Microsoft Outlook as the SMTP Server
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Unlike Gmail, Microsoft Outlook no longer supports app-specific passwords.
 Therefore, OAuth2.0 authentication must be used for Outlook. Also, it only
-supports `XOAUTH2` authentication method.
+supports `XOAUTH2` authentication mechanism.
 
 Edit `~/.gitconfig` to specify your account settings for Outlook and use its
 SMTP server with `git send-email`:
@@ -579,8 +587,7 @@ next time.
 
 If you are using OAuth2.0 authentication, you need to use an access token in
 place of a password when prompted. Various OAuth2.0 token generators are
-available online. Community maintained credential helpers for Gmail and Outlook
-are also available:
+available online. Community maintained credential helpers are also available:
 
 	- https://github.com/AdityaGarg8/git-credential-email[git-credential-gmail]
 	  (cross platform, dedicated helper for authenticating Gmail accounts)
@@ -588,14 +595,24 @@ are also available:
 	- https://github.com/AdityaGarg8/git-credential-email[git-credential-outlook]
 	  (cross platform, dedicated helper for authenticating Microsoft Outlook accounts)
 
+	- https://github.com/AdityaGarg8/git-credential-email[git-credential-yahoo]
+	  (cross platform, dedicated helper for authenticating Yahoo accounts)
+
 You can also see linkgit:gitcredentials[7] for more OAuth based authentication
 helpers.
 
 Note: the following core Perl modules that may be installed with your
 distribution of Perl are required:
-MIME::Base64, MIME::QuotedPrint, Net::Domain and Net::SMTP.
+
+https://metacpan.org/pod/MIME::Base64[MIME::Base64],
+https://metacpan.org/pod/MIME::QuotedPrint[MIME::QuotedPrint],
+https://metacpan.org/pod/Net::Domain[Net::Domain] and
+https://metacpan.org/pod/Net::SMTP[Net::SMTP].
+
 These additional Perl modules are also required:
-Authen::SASL and Mail::Address.
+
+https://metacpan.org/pod/Authen::SASL[Authen::SASL] and
+https://metacpan.org/pod/Mail::Address[Mail::Address].
 
 
 SEE ALSO
diff --git a/Documentation/gitcredentials.adoc b/Documentation/gitcredentials.adoc
index b49923db026fe2..3337bb475de4c5 100644
--- a/Documentation/gitcredentials.adoc
+++ b/Documentation/gitcredentials.adoc
@@ -133,10 +133,6 @@ Popular helpers with OAuth support include:
 
     - https://github.com/hickford/git-credential-oauth[git-credential-oauth] (cross platform, included in many Linux distributions)
 
-    - https://github.com/AdityaGarg8/git-credential-email[git-credential-gmail] (cross platform, dedicated helper to authenticate Gmail accounts for linkgit:git-send-email[1])
-
-    - https://github.com/AdityaGarg8/git-credential-email[git-credential-outlook] (cross platform, dedicated helper to authenticate Microsoft Outlook accounts for linkgit:git-send-email[1])
-
 CREDENTIAL CONTEXTS
 -------------------
 
diff --git a/Documentation/technical/api-path-walk.adoc b/Documentation/technical/api-path-walk.adoc
index 3e089211fb4d69..34c905eb9c3130 100644
--- a/Documentation/technical/api-path-walk.adoc
+++ b/Documentation/technical/api-path-walk.adoc
@@ -56,6 +56,14 @@ better off using the revision walk API instead.
 	the revision walk so that the walk emits commits marked with the
 	`UNINTERESTING` flag.
 
+`edge_aggressive`::
+	For performance reasons, usually only the boundary commits are
+	explored to find UNINTERESTING objects. However, in the case of
+	shallow clones it can be helpful to mark all trees and blobs
+	reachable from UNINTERESTING tip commits as UNINTERESTING. This
+	matches the behavior of `--objects-edge-aggressive` in the
+	revision API.
+
 `pl`::
 	This pattern list pointer allows focusing the path-walk search to
 	a set of patterns, only emitting paths that match the given
@@ -69,4 +77,5 @@ Examples
 
 See example usages in:
 	`t/helper/test-path-walk.c`,
+	`builtin/pack-objects.c`,
 	`builtin/backfill.c`
diff --git a/GIT-VERSION-GEN b/GIT-VERSION-GEN
index 5d17e1ef62ecaf..63463c87739aa0 100755
--- a/GIT-VERSION-GEN
+++ b/GIT-VERSION-GEN
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-DEF_VER=v2.50.0
+DEF_VER=v2.50.GIT
 
 LF='
 '
diff --git a/RelNotes b/RelNotes
index eaaaf878d38ad1..48f15770a4abb8 120000
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/2.50.0.adoc
\ No newline at end of file
+Documentation/RelNotes/2.51.0.adoc
\ No newline at end of file
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 67a5ff2b9ebd29..4b23fcecbd8e7a 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -275,6 +275,7 @@ struct expand_data {
 	struct object_id oid;
 	enum object_type type;
 	unsigned long size;
+	unsigned short mode;
 	off_t disk_size;
 	const char *rest;
 	struct object_id delta_base_oid;
@@ -306,6 +307,7 @@ struct expand_data {
 	 */
 	unsigned skip_object_info : 1;
 };
+#define EXPAND_DATA_INIT  { .mode = S_IFINVALID }
 
 static int is_atom(const char *atom, const char *s, int slen)
 {
@@ -345,6 +347,9 @@ static int expand_atom(struct strbuf *sb, const char *atom, int len,
 		else
 			strbuf_addstr(sb,
 				      oid_to_hex(&data->delta_base_oid));
+	} else if (is_atom("objectmode", atom, len)) {
+		if (!data->mark_query && !(S_IFINVALID == data->mode))
+			strbuf_addf(sb, "%06o", data->mode);
 	} else
 		return 0;
 	return 1;
@@ -491,7 +496,10 @@ static void batch_object_write(const char *obj_name,
 						       &data->oid, &data->info,
 						       OBJECT_INFO_LOOKUP_REPLACE);
 		if (ret < 0) {
-			report_object_status(opt, obj_name, &data->oid, "missing");
+			if (data->mode == S_IFGITLINK)
+				report_object_status(opt, oid_to_hex(&data->oid), &data->oid, "submodule");
+			else
+				report_object_status(opt, obj_name, &data->oid, "missing");
 			return;
 		}
 
@@ -613,6 +621,7 @@ static void batch_one_object(const char *obj_name,
 		goto out;
 	}
 
+	data->mode = ctx.mode;
 	batch_object_write(obj_name, scratch, opt, data, NULL, 0);
 
 out:
@@ -866,7 +875,7 @@ static int batch_objects(struct batch_options *opt)
 {
 	struct strbuf input = STRBUF_INIT;
 	struct strbuf output = STRBUF_INIT;
-	struct expand_data data;
+	struct expand_data data = EXPAND_DATA_INIT;
 	int save_warning;
 	int retval = 0;
 
@@ -875,7 +884,6 @@ static int batch_objects(struct batch_options *opt)
 	 * object_info to be handed to oid_object_info_extended for each
 	 * object.
 	 */
-	memset(&data, 0, sizeof(data));
 	data.mark_query = 1;
 	expand_format(&output,
 		      opt->format ? opt->format : DEFAULT_FORMAT,
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index a783a86e797726..ee48980248fee1 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -311,6 +311,7 @@ static int graph_write(int argc, const char **argv, const char *prefix,
 		while (strbuf_getline(&buf, stdin) != EOF) {
 			if (read_one_commit(&commits, progress, buf.buf)) {
 				result = 1;
+				stop_progress(&progress);
 				goto cleanup;
 			}
 		}
diff --git a/builtin/diff.c b/builtin/diff.c
index fa963808c31848..c6231edce4e822 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -35,7 +35,7 @@ static const char builtin_diff_usage[] =
 "   or: git diff [<options>] [--merge-base] <commit> [<commit>...] <commit> [--] [<path>...]\n"
 "   or: git diff [<options>] <commit>...<commit> [--] [<path>...]\n"
 "   or: git diff [<options>] <blob> <blob>\n"
-"   or: git diff [<options>] --no-index [--] <path> <path>"
+"   or: git diff [<options>] --no-index [--] <path> <path> [<pathspec>...]"
 "\n"
 COMMON_DIFF_OPTIONS_HELP;
 
diff --git a/builtin/fetch-pack.c b/builtin/fetch-pack.c
index d07eec9e5550ab..d9e42bad58430d 100644
--- a/builtin/fetch-pack.c
+++ b/builtin/fetch-pack.c
@@ -274,8 +274,10 @@ int cmd_fetch_pack(int argc,
 	}
 	close(fd[0]);
 	close(fd[1]);
-	if (finish_connect(conn))
-		return 1;
+	if (finish_connect(conn)) {
+		ret = 1;
+		goto cleanup;
+	}
 
 	ret = !fetched_refs;
 
@@ -291,6 +293,7 @@ int cmd_fetch_pack(int argc,
 		printf("%s %s\n",
 		       oid_to_hex(&ref->old_oid), ref->name);
 
+cleanup:
 	for (size_t i = 0; i < nr_sought; i++)
 		free_one_ref(sought_to_free[i]);
 	free(sought_to_free);
diff --git a/builtin/mktag.c b/builtin/mktag.c
index 7ac11c46d53f03..1b1dc0263e188a 100644
--- a/builtin/mktag.c
+++ b/builtin/mktag.c
@@ -41,7 +41,7 @@ static int mktag_fsck_error_func(struct fsck_options *o UNUSED,
 		fprintf_ln(stderr, _("error: tag input does not pass fsck: %s"), message);
 		return 1;
 	default:
-		BUG(_("%d (FSCK_IGNORE?) should never trigger this callback"),
+		BUG("%d (FSCK_IGNORE?) should never trigger this callback",
 		    msg_type);
 	}
 }
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 8b33edc2ff525a..67941c8a603ae4 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -41,6 +41,10 @@
 #include "promisor-remote.h"
 #include "pack-mtimes.h"
 #include "parse-options.h"
+#include "blob.h"
+#include "tree.h"
+#include "path-walk.h"
+#include "trace2.h"
 
 /*
  * Objects we are going to pack are collected in the `to_pack` structure.
@@ -184,8 +188,14 @@ static inline void oe_set_delta_size(struct packing_data *pack,
 #define SET_DELTA_SIBLING(obj, val) oe_set_delta_sibling(&to_pack, obj, val)
 
 static const char *const pack_usage[] = {
-	N_("git pack-objects --stdout [<options>] [< <ref-list> | < <object-list>]"),
-	N_("git pack-objects [<options>] <base-name> [< <ref-list> | < <object-list>]"),
+	N_("git pack-objects [-q | --progress | --all-progress] [--all-progress-implied]\n"
+	   "                 [--no-reuse-delta] [--delta-base-offset] [--non-empty]\n"
+	   "                 [--local] [--incremental] [--window=<n>] [--depth=<n>]\n"
+	   "                 [--revs [--unpacked | --all]] [--keep-pack=<pack-name>]\n"
+	   "                 [--cruft] [--cruft-expiration=<time>]\n"
+	   "                 [--stdout [--filter=<filter-spec>] | <base-name>]\n"
+	   "                 [--shallow] [--keep-true-parents] [--[no-]sparse]\n"
+	   "                 [--name-hash-version=<n>] [--path-walk] < <object-list>"),
 	NULL
 };
 
@@ -200,6 +210,7 @@ static int keep_unreachable, unpack_unreachable, include_tag;
 static timestamp_t unpack_unreachable_expiration;
 static int pack_loose_unreachable;
 static int cruft;
+static int shallow = 0;
 static timestamp_t cruft_expiration;
 static int local;
 static int have_non_local_packs;
@@ -218,6 +229,7 @@ static int delta_search_threads;
 static int pack_to_stdout;
 static int sparse;
 static int thin;
+static int path_walk = -1;
 static int num_preferred_base;
 static struct progress *progress_state;
 
@@ -3041,6 +3053,7 @@ static void find_deltas(struct object_entry **list, unsigned *list_size,
 struct thread_params {
 	pthread_t thread;
 	struct object_entry **list;
+	struct packing_region *regions;
 	unsigned list_size;
 	unsigned remaining;
 	int window;
@@ -3283,6 +3296,242 @@ static int add_ref_tag(const char *tag UNUSED, const char *referent UNUSED, cons
 	return 0;
 }
 
+static int should_attempt_deltas(struct object_entry *entry)
+{
+	if (DELTA(entry))
+		/* This happens if we decided to reuse existing
+		 * delta from a pack. "reuse_delta &&" is implied.
+		 */
+		return 0;
+
+	if (!entry->type_valid ||
+	    oe_size_less_than(&to_pack, entry, 50))
+		return 0;
+
+	if (entry->no_try_delta)
+		return 0;
+
+	if (!entry->preferred_base) {
+		if (oe_type(entry) < 0)
+			die(_("unable to get type of object %s"),
+				oid_to_hex(&entry->idx.oid));
+	} else if (oe_type(entry) < 0) {
+		/*
+		 * This object is not found, but we
+		 * don't have to include it anyway.
+		 */
+		return 0;
+	}
+
+	return 1;
+}
+
+static void find_deltas_for_region(struct object_entry *list,
+				   struct packing_region *region,
+				   unsigned int *processed)
+{
+	struct object_entry **delta_list;
+	unsigned int delta_list_nr = 0;
+
+	ALLOC_ARRAY(delta_list, region->nr);
+	for (size_t i = 0; i < region->nr; i++) {
+		struct object_entry *entry = list + region->start + i;
+		if (should_attempt_deltas(entry))
+			delta_list[delta_list_nr++] = entry;
+	}
+
+	QSORT(delta_list, delta_list_nr, type_size_sort);
+	find_deltas(delta_list, &delta_list_nr, window, depth, processed);
+	free(delta_list);
+}
+
+static void find_deltas_by_region(struct object_entry *list,
+				  struct packing_region *regions,
+				  size_t start, size_t nr)
+{
+	unsigned int processed = 0;
+	size_t progress_nr;
+
+	if (!nr)
+		return;
+
+	progress_nr = regions[nr - 1].start + regions[nr - 1].nr;
+
+	if (progress)
+		progress_state = start_progress(the_repository,
+						_("Compressing objects by path"),
+						progress_nr);
+
+	while (nr--)
+		find_deltas_for_region(list,
+				       &regions[start++],
+				       &processed);
+
+	display_progress(progress_state, progress_nr);
+	stop_progress(&progress_state);
+}
+
+static void *threaded_find_deltas_by_path(void *arg)
+{
+	struct thread_params *me = arg;
+
+	progress_lock();
+	while (me->remaining) {
+		while (me->remaining) {
+			progress_unlock();
+			find_deltas_for_region(to_pack.objects,
+					       me->regions,
+					       me->processed);
+			progress_lock();
+			me->remaining--;
+			me->regions++;
+		}
+
+		me->working = 0;
+		pthread_cond_signal(&progress_cond);
+		progress_unlock();
+
+		/*
+		 * We must not set ->data_ready before we wait on the
+		 * condition because the main thread may have set it to 1
+		 * before we get here. In order to be sure that new
+		 * work is available if we see 1 in ->data_ready, it
+		 * was initialized to 0 before this thread was spawned
+		 * and we reset it to 0 right away.
+		 */
+		pthread_mutex_lock(&me->mutex);
+		while (!me->data_ready)
+			pthread_cond_wait(&me->cond, &me->mutex);
+		me->data_ready = 0;
+		pthread_mutex_unlock(&me->mutex);
+
+		progress_lock();
+	}
+	progress_unlock();
+	/* leave ->working 1 so that this doesn't get more work assigned */
+	return NULL;
+}
+
+static void ll_find_deltas_by_region(struct object_entry *list,
+				     struct packing_region *regions,
+				     uint32_t start, uint32_t nr)
+{
+	struct thread_params *p;
+	int i, ret, active_threads = 0;
+	unsigned int processed = 0;
+	uint32_t progress_nr;
+	init_threaded_search();
+
+	if (!nr)
+		return;
+
+	progress_nr =  regions[nr - 1].start + regions[nr - 1].nr;
+	if (delta_search_threads <= 1) {
+		find_deltas_by_region(list, regions, start, nr);
+		cleanup_threaded_search();
+		return;
+	}
+
+	if (progress > pack_to_stdout)
+		fprintf_ln(stderr,
+			   Q_("Path-based delta compression using up to %d thread",
+			      "Path-based delta compression using up to %d threads",
+			      delta_search_threads),
+			   delta_search_threads);
+	CALLOC_ARRAY(p, delta_search_threads);
+
+	if (progress)
+		progress_state = start_progress(the_repository,
+						_("Compressing objects by path"),
+						progress_nr);
+	/* Partition the work amongst work threads. */
+	for (i = 0; i < delta_search_threads; i++) {
+		unsigned sub_size = nr / (delta_search_threads - i);
+
+		p[i].window = window;
+		p[i].depth = depth;
+		p[i].processed = &processed;
+		p[i].working = 1;
+		p[i].data_ready = 0;
+
+		p[i].regions = regions;
+		p[i].list_size = sub_size;
+		p[i].remaining = sub_size;
+
+		regions += sub_size;
+		nr -= sub_size;
+	}
+
+	/* Start work threads. */
+	for (i = 0; i < delta_search_threads; i++) {
+		if (!p[i].list_size)
+			continue;
+		pthread_mutex_init(&p[i].mutex, NULL);
+		pthread_cond_init(&p[i].cond, NULL);
+		ret = pthread_create(&p[i].thread, NULL,
+				     threaded_find_deltas_by_path, &p[i]);
+		if (ret)
+			die(_("unable to create thread: %s"), strerror(ret));
+		active_threads++;
+	}
+
+	/*
+	 * Now let's wait for work completion.  Each time a thread is done
+	 * with its work, we steal half of the remaining work from the
+	 * thread with the largest number of unprocessed objects and give
+	 * it to that newly idle thread.  This ensure good load balancing
+	 * until the remaining object list segments are simply too short
+	 * to be worth splitting anymore.
+	 */
+	while (active_threads) {
+		struct thread_params *target = NULL;
+		struct thread_params *victim = NULL;
+		unsigned sub_size = 0;
+
+		progress_lock();
+		for (;;) {
+			for (i = 0; !target && i < delta_search_threads; i++)
+				if (!p[i].working)
+					target = &p[i];
+			if (target)
+				break;
+			pthread_cond_wait(&progress_cond, &progress_mutex);
+		}
+
+		for (i = 0; i < delta_search_threads; i++)
+			if (p[i].remaining > 2*window &&
+			    (!victim || victim->remaining < p[i].remaining))
+				victim = &p[i];
+		if (victim) {
+			sub_size = victim->remaining / 2;
+			target->regions = victim->regions + victim->remaining - sub_size;
+			victim->list_size -= sub_size;
+			victim->remaining -= sub_size;
+		}
+		target->list_size = sub_size;
+		target->remaining = sub_size;
+		target->working = 1;
+		progress_unlock();
+
+		pthread_mutex_lock(&target->mutex);
+		target->data_ready = 1;
+		pthread_cond_signal(&target->cond);
+		pthread_mutex_unlock(&target->mutex);
+
+		if (!sub_size) {
+			pthread_join(target->thread, NULL);
+			pthread_cond_destroy(&target->cond);
+			pthread_mutex_destroy(&target->mutex);
+			active_threads--;
+		}
+	}
+	cleanup_threaded_search();
+	free(p);
+
+	display_progress(progress_state, progress_nr);
+	stop_progress(&progress_state);
+}
+
 static void prepare_pack(int window, int depth)
 {
 	struct object_entry **delta_list;
@@ -3307,39 +3556,21 @@ static void prepare_pack(int window, int depth)
 	if (!to_pack.nr_objects || !window || !depth)
 		return;
 
+	if (path_walk)
+		ll_find_deltas_by_region(to_pack.objects, to_pack.regions,
+					 0, to_pack.nr_regions);
+
 	ALLOC_ARRAY(delta_list, to_pack.nr_objects);
 	nr_deltas = n = 0;
 
 	for (i = 0; i < to_pack.nr_objects; i++) {
 		struct object_entry *entry = to_pack.objects + i;
 
-		if (DELTA(entry))
-			/* This happens if we decided to reuse existing
-			 * delta from a pack.  "reuse_delta &&" is implied.
-			 */
-			continue;
-
-		if (!entry->type_valid ||
-		    oe_size_less_than(&to_pack, entry, 50))
-			continue;
-
-		if (entry->no_try_delta)
+		if (!should_attempt_deltas(entry))
 			continue;
 
-		if (!entry->preferred_base) {
+		if (!entry->preferred_base)
 			nr_deltas++;
-			if (oe_type(entry) < 0)
-				die(_("unable to get type of object %s"),
-				    oid_to_hex(&entry->idx.oid));
-		} else {
-			if (oe_type(entry) < 0) {
-				/*
-				 * This object is not found, but we
-				 * don't have to include it anyway.
-				 */
-				continue;
-			}
-		}
 
 		delta_list[n++] = entry;
 	}
@@ -4272,6 +4503,93 @@ static void mark_bitmap_preferred_tips(void)
 	}
 }
 
+static inline int is_oid_uninteresting(struct repository *repo,
+				       struct object_id *oid)
+{
+	struct object *o = lookup_object(repo, oid);
+	return !o || (o->flags & UNINTERESTING);
+}
+
+static int add_objects_by_path(const char *path,
+			       struct oid_array *oids,
+			       enum object_type type,
+			       void *data)
+{
+	size_t oe_start = to_pack.nr_objects;
+	size_t oe_end;
+	unsigned int *processed = data;
+
+	/*
+	 * First, add all objects to the packing data, including the ones
+	 * marked UNINTERESTING (translated to 'exclude') as they can be
+	 * used as delta bases.
+	 */
+	for (size_t i = 0; i < oids->nr; i++) {
+		int exclude;
+		struct object_info oi = OBJECT_INFO_INIT;
+		struct object_id *oid = &oids->oid[i];
+
+		/* Skip objects that do not exist locally. */
+		if ((exclude_promisor_objects || arg_missing_action != MA_ERROR) &&
+		    oid_object_info_extended(the_repository, oid, &oi,
+					     OBJECT_INFO_FOR_PREFETCH) < 0)
+			continue;
+
+		exclude = is_oid_uninteresting(the_repository, oid);
+
+		if (exclude && !thin)
+			continue;
+
+		add_object_entry(oid, type, path, exclude);
+	}
+
+	oe_end = to_pack.nr_objects;
+
+	/* We can skip delta calculations if it is a no-op. */
+	if (oe_end == oe_start || !window)
+		return 0;
+
+	ALLOC_GROW(to_pack.regions,
+		   to_pack.nr_regions + 1,
+		   to_pack.nr_regions_alloc);
+
+	to_pack.regions[to_pack.nr_regions].start = oe_start;
+	to_pack.regions[to_pack.nr_regions].nr = oe_end - oe_start;
+	to_pack.nr_regions++;
+
+	*processed += oids->nr;
+	display_progress(progress_state, *processed);
+
+	return 0;
+}
+
+static void get_object_list_path_walk(struct rev_info *revs)
+{
+	struct path_walk_info info = PATH_WALK_INFO_INIT;
+	unsigned int processed = 0;
+	int result;
+
+	info.revs = revs;
+	info.path_fn = add_objects_by_path;
+	info.path_fn_data = &processed;
+
+	/*
+	 * Allow the --[no-]sparse option to be interesting here, if only
+	 * for testing purposes. Paths with no interesting objects will not
+	 * contribute to the resulting pack, but only create noisy preferred
+	 * base objects.
+	 */
+	info.prune_all_uninteresting = sparse;
+	info.edge_aggressive = shallow;
+
+	trace2_region_enter("pack-objects", "path-walk", revs->repo);
+	result = walk_objects_by_path(&info);
+	trace2_region_leave("pack-objects", "path-walk", revs->repo);
+
+	if (result)
+		die(_("failed to pack objects via path-walk"));
+}
+
 static void get_object_list(struct rev_info *revs, int ac, const char **av)
 {
 	struct setup_revision_opt s_r_opt = {
@@ -4327,15 +4645,19 @@ static void get_object_list(struct rev_info *revs, int ac, const char **av)
 	if (write_bitmap_index)
 		mark_bitmap_preferred_tips();
 
-	if (prepare_revision_walk(revs))
-		die(_("revision walk setup failed"));
-	mark_edges_uninteresting(revs, show_edge, sparse);
-
 	if (!fn_show_object)
 		fn_show_object = show_object;
-	traverse_commit_list(revs,
-			     show_commit, fn_show_object,
-			     NULL);
+
+	if (path_walk) {
+		get_object_list_path_walk(revs);
+	} else {
+		if (prepare_revision_walk(revs))
+			die(_("revision walk setup failed"));
+		mark_edges_uninteresting(revs, show_edge, sparse);
+		traverse_commit_list(revs,
+				show_commit, fn_show_object,
+				NULL);
+	}
 
 	if (unpack_unreachable_expiration) {
 		revs->ignore_missing_links = 1;
@@ -4464,7 +4786,6 @@ int cmd_pack_objects(int argc,
 		     struct repository *repo UNUSED)
 {
 	int use_internal_rev_list = 0;
-	int shallow = 0;
 	int all_progress_implied = 0;
 	struct strvec rp = STRVEC_INIT;
 	int rev_list_unpacked = 0, rev_list_all = 0, rev_list_reflog = 0;
@@ -4545,6 +4866,8 @@ int cmd_pack_objects(int argc,
 			 N_("use the sparse reachability algorithm")),
 		OPT_BOOL(0, "thin", &thin,
 			 N_("create thin packs")),
+		OPT_BOOL(0, "path-walk", &path_walk,
+			 N_("use the path-walk API to walk objects when possible")),
 		OPT_BOOL(0, "shallow", &shallow,
 			 N_("create packs suitable for shallow fetches")),
 		OPT_BOOL(0, "honor-pack-keep", &ignore_packed_keep_on_disk,
@@ -4614,6 +4937,17 @@ int cmd_pack_objects(int argc,
 	if (pack_to_stdout != !base_name || argc)
 		usage_with_options(pack_usage, pack_objects_options);
 
+	if (path_walk < 0) {
+		if (use_bitmap_index > 0 ||
+		    !use_internal_rev_list)
+			path_walk = 0;
+		else if (the_repository->gitdir &&
+			 the_repository->settings.pack_use_path_walk)
+			path_walk = 1;
+		else
+			path_walk = git_env_bool("GIT_TEST_PACK_PATH_WALK", 0);
+	}
+
 	if (depth < 0)
 		depth = 0;
 	if (depth >= (1 << OE_DEPTH_BITS)) {
@@ -4630,7 +4964,28 @@ int cmd_pack_objects(int argc,
 		window = 0;
 
 	strvec_push(&rp, "pack-objects");
-	if (thin) {
+
+	if (path_walk) {
+		const char *option = NULL;
+		if (filter_options.choice)
+			option = "--filter";
+		else if (use_delta_islands)
+			option = "--delta-islands";
+
+		if (option) {
+			warning(_("cannot use %s with %s"),
+				option, "--path-walk");
+			path_walk = 0;
+		}
+	}
+	if (path_walk) {
+		strvec_push(&rp, "--boundary");
+		 /*
+		  * We must disable the bitmaps because we are removing
+		  * the --objects / --objects-edge[-aggressive] options.
+		  */
+		use_bitmap_index = 0;
+	} else if (thin) {
 		use_internal_rev_list = 1;
 		strvec_push(&rp, shallow
 				? "--objects-edge-aggressive"
diff --git a/builtin/repack.c b/builtin/repack.c
index 59214dbdfdfcd5..5ddc6e7f9573d4 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -43,7 +43,7 @@ static char *packdir, *packtmp_name, *packtmp;
 static const char *const git_repack_usage[] = {
 	N_("git repack [-a] [-A] [-d] [-f] [-F] [-l] [-n] [-q] [-b] [-m]\n"
 	   "[--window=<n>] [--depth=<n>] [--threads=<n>] [--keep-pack=<pack-name>]\n"
-	   "[--write-midx] [--name-hash-version=<n>]"),
+	   "[--write-midx] [--name-hash-version=<n>] [--path-walk]"),
 	NULL
 };
 
@@ -63,6 +63,7 @@ struct pack_objects_args {
 	int quiet;
 	int local;
 	int name_hash_version;
+	int path_walk;
 	struct list_objects_filter_options filter_options;
 };
 
@@ -313,6 +314,8 @@ static void prepare_pack_objects(struct child_process *cmd,
 		strvec_pushf(&cmd->args, "--no-reuse-object");
 	if (args->name_hash_version)
 		strvec_pushf(&cmd->args, "--name-hash-version=%d", args->name_hash_version);
+	if (args->path_walk)
+		strvec_pushf(&cmd->args, "--path-walk");
 	if (args->local)
 		strvec_push(&cmd->args,  "--local");
 	if (args->quiet)
@@ -1184,6 +1187,8 @@ int cmd_repack(int argc,
 				N_("pass --no-reuse-object to git-pack-objects")),
 		OPT_INTEGER(0, "name-hash-version", &po_args.name_hash_version,
 				N_("specify the name hash version to use for grouping similar objects by path")),
+		OPT_BOOL(0, "path-walk", &po_args.path_walk,
+				N_("pass --path-walk to git-pack-objects")),
 		OPT_NEGBIT('n', NULL, &run_update_server_info,
 				N_("do not run git-update-server-info"), 1),
 		OPT__QUIET(&po_args.quiet, N_("be quiet")),
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 88a36ea9f8674e..2dceeeed8bd03c 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -621,7 +621,7 @@ static void print_preparing_worktree_line(int detach,
 		else {
 			struct commit *commit = lookup_commit_reference_by_name(branch);
 			if (!commit)
-				BUG(_("unreachable: invalid reference: %s"), branch);
+				BUG("unreachable: invalid reference: %s", branch);
 			fprintf_ln(stderr, _("Preparing worktree (detached HEAD %s)"),
 				  repo_find_unique_abbrev(the_repository, &commit->object.oid, DEFAULT_ABBREV));
 		}
diff --git a/contrib/credential/netrc/meson.build b/contrib/credential/netrc/meson.build
index 3d74547c8aea30..16fa69e317e30e 100644
--- a/contrib/credential/netrc/meson.build
+++ b/contrib/credential/netrc/meson.build
@@ -17,6 +17,6 @@ if get_option('tests')
     workdir: meson.current_source_dir(),
     env: credential_netrc_testenv,
     depends: test_dependencies + bin_wrappers + [credential_netrc],
-    timeout: 0,
+    kwargs: test_kwargs,
   )
 endif
diff --git a/contrib/subtree/meson.build b/contrib/subtree/meson.build
index 63714166a61f89..98dd8e0c8eacea 100644
--- a/contrib/subtree/meson.build
+++ b/contrib/subtree/meson.build
@@ -21,7 +21,7 @@ if get_option('tests')
     env: subtree_test_environment,
     workdir: meson.current_source_dir() / 't',
     depends: test_dependencies + bin_wrappers + [ git_subtree ],
-    timeout: 0,
+    kwargs: test_kwargs,
   )
 endif
 
diff --git a/diff-no-index.c b/diff-no-index.c
index 9739b2b268b93c..4aeeb98cfa8fba 100644
--- a/diff-no-index.c
+++ b/diff-no-index.c
@@ -15,20 +15,45 @@
 #include "gettext.h"
 #include "revision.h"
 #include "parse-options.h"
+#include "pathspec.h"
 #include "string-list.h"
 #include "dir.h"
 
-static int read_directory_contents(const char *path, struct string_list *list)
+static int read_directory_contents(const char *path, struct string_list *list,
+				   const struct pathspec *pathspec,
+				   int skip)
 {
+	struct strbuf match = STRBUF_INIT;
+	int len;
 	DIR *dir;
 	struct dirent *e;
 
 	if (!(dir = opendir(path)))
 		return error("Could not open directory %s", path);
 
-	while ((e = readdir_skip_dot_and_dotdot(dir)))
+	if (pathspec) {
+		strbuf_addstr(&match, path);
+		strbuf_complete(&match, '/');
+		strbuf_remove(&match, 0, skip);
+
+		len = match.len;
+	}
+
+	while ((e = readdir_skip_dot_and_dotdot(dir))) {
+		if (pathspec) {
+			strbuf_setlen(&match, len);
+			strbuf_addstr(&match, e->d_name);
+
+			if (!match_leading_pathspec(NULL, pathspec,
+						    match.buf, match.len,
+						    0, NULL, e->d_type == DT_DIR ? 1 : 0))
+				continue;
+		}
+
 		string_list_insert(list, e->d_name);
+	}
 
+	strbuf_release(&match);
 	closedir(dir);
 	return 0;
 }
@@ -131,7 +156,8 @@ static struct diff_filespec *noindex_filespec(const struct git_hash_algo *algop,
 }
 
 static int queue_diff(struct diff_options *o, const struct git_hash_algo *algop,
-		      const char *name1, const char *name2, int recursing)
+		      const char *name1, const char *name2, int recursing,
+		      const struct pathspec *ps, int skip1, int skip2)
 {
 	int mode1 = 0, mode2 = 0;
 	enum special special1 = SPECIAL_NONE, special2 = SPECIAL_NONE;
@@ -171,9 +197,9 @@ static int queue_diff(struct diff_options *o, const struct git_hash_algo *algop,
 		int i1, i2, ret = 0;
 		size_t len1 = 0, len2 = 0;
 
-		if (name1 && read_directory_contents(name1, &p1))
+		if (name1 && read_directory_contents(name1, &p1, ps, skip1))
 			return -1;
-		if (name2 && read_directory_contents(name2, &p2)) {
+		if (name2 && read_directory_contents(name2, &p2, ps, skip2)) {
 			string_list_clear(&p1, 0);
 			return -1;
 		}
@@ -218,7 +244,7 @@ static int queue_diff(struct diff_options *o, const struct git_hash_algo *algop,
 				n2 = buffer2.buf;
 			}
 
-			ret = queue_diff(o, algop, n1, n2, 1);
+			ret = queue_diff(o, algop, n1, n2, 1, ps, skip1, skip2);
 		}
 		string_list_clear(&p1, 0);
 		string_list_clear(&p2, 0);
@@ -258,8 +284,10 @@ static void append_basename(struct strbuf *path, const char *dir, const char *fi
  * DWIM "diff D F" into "diff D/F F" and "diff F D" into "diff F D/F"
  * Note that we append the basename of F to D/, so "diff a/b/file D"
  * becomes "diff a/b/file D/file", not "diff a/b/file D/a/b/file".
+ *
+ * Return 1 if both paths are directories, 0 otherwise.
  */
-static void fixup_paths(const char **path, struct strbuf *replacement)
+static int fixup_paths(const char **path, struct strbuf *replacement)
 {
 	struct stat st;
 	unsigned int isdir0 = 0, isdir1 = 0;
@@ -282,26 +310,31 @@ static void fixup_paths(const char **path, struct strbuf *replacement)
 	if ((isdir0 && ispipe1) || (ispipe0 && isdir1))
 		die(_("cannot compare a named pipe to a directory"));
 
-	if (isdir0 == isdir1)
-		return;
+	/* if both paths are directories, we will enable pathspecs */
+	if (isdir0 && isdir1)
+		return 1;
+
 	if (isdir0) {
 		append_basename(replacement, path[0], path[1]);
 		path[0] = replacement->buf;
-	} else {
+	} else if (isdir1) {
 		append_basename(replacement, path[1], path[0]);
 		path[1] = replacement->buf;
 	}
+
+	return 0;
 }
 
 static const char * const diff_no_index_usage[] = {
-	N_("git diff --no-index [<options>] <path> <path>"),
+	N_("git diff --no-index [<options>] <path> <path> [<pathspec>...]"),
 	NULL
 };
 
 int diff_no_index(struct rev_info *revs, const struct git_hash_algo *algop,
 		  int implicit_no_index, int argc, const char **argv)
 {
-	int i, no_index;
+	struct pathspec pathspec, *ps = NULL;
+	int i, no_index, skip1 = 0, skip2 = 0;
 	int ret = 1;
 	const char *paths[2];
 	char *to_free[ARRAY_SIZE(paths)] = { 0 };
@@ -317,13 +350,12 @@ int diff_no_index(struct rev_info *revs, const struct git_hash_algo *algop,
 	options = add_diff_options(no_index_options, &revs->diffopt);
 	argc = parse_options(argc, argv, revs->prefix, options,
 			     diff_no_index_usage, 0);
-	if (argc != 2) {
+	if (argc < 2) {
 		if (implicit_no_index)
 			warning(_("Not a git repository. Use --no-index to "
 				  "compare two paths outside a working tree"));
 		usage_with_options(diff_no_index_usage, options);
 	}
-	FREE_AND_NULL(options);
 	for (i = 0; i < 2; i++) {
 		const char *p = argv[i];
 		if (!strcmp(p, "-"))
@@ -337,7 +369,23 @@ int diff_no_index(struct rev_info *revs, const struct git_hash_algo *algop,
 		paths[i] = p;
 	}
 
-	fixup_paths(paths, &replacement);
+	if (fixup_paths(paths, &replacement)) {
+		parse_pathspec(&pathspec, PATHSPEC_FROMTOP | PATHSPEC_ATTR,
+			       PATHSPEC_PREFER_FULL | PATHSPEC_NO_REPOSITORY,
+			       NULL, &argv[2]);
+		if (pathspec.nr)
+			ps = &pathspec;
+
+		skip1 = strlen(paths[0]);
+		skip1 += paths[0][skip1] == '/' ? 0 : 1;
+		skip2 = strlen(paths[1]);
+		skip2 += paths[1][skip2] == '/' ? 0 : 1;
+	} else if (argc > 2) {
+		warning(_("Limiting comparison with pathspecs is only "
+			  "supported if both paths are directories."));
+		usage_with_options(diff_no_index_usage, options);
+	}
+	FREE_AND_NULL(options);
 
 	revs->diffopt.skip_stat_unmatch = 1;
 	if (!revs->diffopt.output_format)
@@ -354,7 +402,8 @@ int diff_no_index(struct rev_info *revs, const struct git_hash_algo *algop,
 	setup_diff_pager(&revs->diffopt);
 	revs->diffopt.flags.exit_with_status = 1;
 
-	if (queue_diff(&revs->diffopt, algop, paths[0], paths[1], 0))
+	if (queue_diff(&revs->diffopt, algop, paths[0], paths[1], 0, ps,
+		       skip1, skip2))
 		goto out;
 	diff_set_mnemonic_prefix(&revs->diffopt, "1/", "2/");
 	diffcore_std(&revs->diffopt);
@@ -370,5 +419,7 @@ int diff_no_index(struct rev_info *revs, const struct git_hash_algo *algop,
 	for (i = 0; i < ARRAY_SIZE(to_free); i++)
 		free(to_free[i]);
 	strbuf_release(&replacement);
+	if (ps)
+		clear_pathspec(ps);
 	return ret;
 }
diff --git a/dir.c b/dir.c
index a374972b6243b6..c8c869faed2b8d 100644
--- a/dir.c
+++ b/dir.c
@@ -397,9 +397,12 @@ static int match_pathspec_item(struct index_state *istate,
 	    strncmp(item->match, name - prefix, item->prefix))
 		return 0;
 
-	if (item->attr_match_nr &&
-	    !match_pathspec_attrs(istate, name - prefix, namelen + prefix, item))
-		return 0;
+	if (item->attr_match_nr) {
+		if (!istate)
+			BUG("magic PATHSPEC_ATTR requires an index");
+		if (!match_pathspec_attrs(istate, name - prefix, namelen + prefix, item))
+			return 0;
+	}
 
 	/* If the match was just the prefix, we matched */
 	if (!*match)
@@ -577,6 +580,16 @@ int match_pathspec(struct index_state *istate,
 					 prefix, seen, flags);
 }
 
+int match_leading_pathspec(struct index_state *istate,
+			   const struct pathspec *ps,
+			   const char *name, int namelen,
+			   int prefix, char *seen, int is_dir)
+{
+	unsigned flags = is_dir ? DO_MATCH_DIRECTORY | DO_MATCH_LEADING_PATHSPEC : 0;
+	return match_pathspec_with_flags(istate, ps, name, namelen,
+					 prefix, seen, flags);
+}
+
 /**
  * Check if a submodule is a superset of the pathspec
  */
diff --git a/meson.build b/meson.build
index 596f5ac7110ebf..7fea4a34d684c5 100644
--- a/meson.build
+++ b/meson.build
@@ -2054,6 +2054,18 @@ subdir('templates')
 # can properly set up test dependencies. The bin-wrappers themselves are set up
 # at configuration time, so these are fine.
 if get_option('tests')
+  test_kwargs = {
+    'timeout': 0,
+  }
+
+  # The TAP protocol was already understood by previous versions of Meson, but
+  # it was incompatible with the `meson test --interactive` flag.
+  if meson.version().version_compare('>=1.8.0')
+    test_kwargs += {
+      'protocol': 'tap',
+    }
+  endif
+
   subdir('t')
 endif
 
diff --git a/pack-bitmap-write.c b/pack-bitmap-write.c
index 7f400ee01213da..56960e6ad7600a 100644
--- a/pack-bitmap-write.c
+++ b/pack-bitmap-write.c
@@ -1087,7 +1087,7 @@ void bitmap_writer_finish(struct bitmap_writer *writer,
 					 oid_access);
 
 		if (commit_pos < 0)
-			BUG(_("trying to write commit not in index"));
+			BUG("trying to write commit not in index");
 		stored->commit_pos = commit_pos + base_objects;
 	}
 
diff --git a/pack-objects.h b/pack-objects.h
index 475a2d67ce30eb..b1c3e702f4a353 100644
--- a/pack-objects.h
+++ b/pack-objects.h
@@ -120,11 +120,23 @@ struct object_entry {
 	unsigned ext_base:1; /* delta_idx points outside packlist */
 };
 
+/**
+ * A packing region is a section of the packing_data.objects array
+ * as given by a starting index and a number of elements.
+ */
+struct packing_region {
+	size_t start;
+	size_t nr;
+};
+
 struct packing_data {
 	struct repository *repo;
 	struct object_entry *objects;
 	uint32_t nr_objects, nr_alloc;
 
+	struct packing_region *regions;
+	size_t nr_regions, nr_regions_alloc;
+
 	int32_t *index;
 	uint32_t index_size;
 
diff --git a/path-walk.c b/path-walk.c
index 341bdd2ba4ef46..2d4ddbadd50f78 100644
--- a/path-walk.c
+++ b/path-walk.c
@@ -503,7 +503,11 @@ int walk_objects_by_path(struct path_walk_info *info)
 	if (prepare_revision_walk(info->revs))
 		die(_("failed to setup revision walk"));
 
-	/* Walk trees to mark them as UNINTERESTING. */
+	/*
+	 * Walk trees to mark them as UNINTERESTING.
+	 * This is particularly important when 'edge_aggressive' is set.
+	 */
+	info->revs->edge_hint_aggressive = info->edge_aggressive;
 	edge_repo = info->revs->repo;
 	edge_tree_list = root_tree_list;
 	mark_edges_uninteresting(info->revs, show_edge,
diff --git a/path-walk.h b/path-walk.h
index 473ee9d361c864..5ef5a8440e6b5e 100644
--- a/path-walk.h
+++ b/path-walk.h
@@ -50,6 +50,13 @@ struct path_walk_info {
 	 */
 	int prune_all_uninteresting;
 
+	/**
+	 * When 'edge_aggressive' is set, then the revision walk will use
+	 * the '--object-edge-aggressive' option to mark even more objects
+	 * as uninteresting.
+	 */
+	int edge_aggressive;
+
 	/**
 	 * Specify a sparse-checkout definition to match our paths to. Do not
 	 * walk outside of this sparse definition. If the patterns are in
diff --git a/pathspec.c b/pathspec.c
index 2b4e434bc0aa49..a3ddd701c740c9 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -492,7 +492,7 @@ static void init_pathspec_item(struct pathspec_item *item, unsigned flags,
 		if (!match) {
 			const char *hint_path;
 
-			if (!have_git_dir())
+			if ((flags & PATHSPEC_NO_REPOSITORY) || !have_git_dir())
 				die(_("'%s' is outside the directory tree"),
 				    copyfrom);
 			hint_path = repo_get_work_tree(the_repository);
@@ -614,6 +614,10 @@ void parse_pathspec(struct pathspec *pathspec,
 	    (flags & PATHSPEC_PREFER_FULL))
 		BUG("PATHSPEC_PREFER_CWD and PATHSPEC_PREFER_FULL are incompatible");
 
+	if ((flags & PATHSPEC_NO_REPOSITORY) &&
+	    (~magic_mask & (PATHSPEC_ATTR | PATHSPEC_FROMTOP)))
+		BUG("PATHSPEC_NO_REPOSITORY is incompatible with PATHSPEC_ATTR and PATHSPEC_FROMTOP");
+
 	/* No arguments with prefix -> prefix pathspec */
 	if (!entry) {
 		if (flags & PATHSPEC_PREFER_FULL)
diff --git a/pathspec.h b/pathspec.h
index de537cff3cb695..5e3a6f1fe7b7c5 100644
--- a/pathspec.h
+++ b/pathspec.h
@@ -76,6 +76,11 @@ struct pathspec {
  * allowed, then it will automatically set for every pathspec.
  */
 #define PATHSPEC_LITERAL_PATH (1<<6)
+/*
+ * For git diff --no-index, indicate that we are operating without
+ * a repository or index.
+ */
+#define PATHSPEC_NO_REPOSITORY (1<<7)
 
 /**
  * Given command line arguments and a prefix, convert the input to
@@ -184,6 +189,12 @@ int match_pathspec(struct index_state *istate,
 		   const char *name, int namelen,
 		   int prefix, char *seen, int is_dir);
 
+/* Set both DO_MATCH_DIRECTORY and DO_MATCH_LEADING_PATHSPEC if is_dir true */
+int match_leading_pathspec(struct index_state *istate,
+			   const struct pathspec *ps,
+			   const char *name, int namelen,
+			   int prefix, char *seen, int is_dir);
+
 /*
  * Determine whether a pathspec will match only entire index entries (non-sparse
  * files and/or entire sparse directories). If the pathspec has the potential to
diff --git a/repo-settings.c b/repo-settings.c
index 4129f8fb2b43a3..195c24e9c07606 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -54,11 +54,13 @@ void prepare_repo_settings(struct repository *r)
 		r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_SKIPPING;
 		r->settings.pack_use_bitmap_boundary_traversal = 1;
 		r->settings.pack_use_multi_pack_reuse = 1;
+		r->settings.pack_use_path_walk = 1;
 	}
 	if (manyfiles) {
 		r->settings.index_version = 4;
 		r->settings.index_skip_hash = 1;
 		r->settings.core_untracked_cache = UNTRACKED_CACHE_WRITE;
+		r->settings.pack_use_path_walk = 1;
 	}
 
 	/* Commit graph config or default, does not cascade (simple) */
@@ -73,6 +75,7 @@ void prepare_repo_settings(struct repository *r)
 
 	/* Boolean config or default, does not cascade (simple)  */
 	repo_cfg_bool(r, "pack.usesparse", &r->settings.pack_use_sparse, 1);
+	repo_cfg_bool(r, "pack.usepathwalk", &r->settings.pack_use_path_walk, 0);
 	repo_cfg_bool(r, "core.multipackindex", &r->settings.core_multi_pack_index, 1);
 	repo_cfg_bool(r, "index.sparse", &r->settings.sparse_index, 0);
 	repo_cfg_bool(r, "index.skiphash", &r->settings.index_skip_hash, r->settings.index_skip_hash);
diff --git a/repo-settings.h b/repo-settings.h
index 2bf24b259735c2..d4778855614497 100644
--- a/repo-settings.h
+++ b/repo-settings.h
@@ -56,6 +56,7 @@ struct repo_settings {
 	enum untracked_cache_setting core_untracked_cache;
 
 	int pack_use_sparse;
+	int pack_use_path_walk;
 	enum fetch_negotiation_setting fetch_negotiation_algorithm;
 
 	int core_multi_pack_index;
diff --git a/scalar.c b/scalar.c
index 355baf75e499cb..0dc79fa9fb07a5 100644
--- a/scalar.c
+++ b/scalar.c
@@ -170,6 +170,7 @@ static int set_recommended_config(int reconfigure)
 		{ "core.autoCRLF", "false" },
 		{ "core.safeCRLF", "false" },
 		{ "fetch.showForcedUpdates", "false" },
+		{ "pack.usePathWalk", "true" },
 		{ NULL, NULL },
 	};
 	int i;
diff --git a/sequencer.c b/sequencer.c
index 1ee0abbd4514f2..9456ca6ee97db4 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2067,6 +2067,9 @@ static int update_squash_messages(struct repository *r,
 	const char *message, *body;
 	const char *encoding = get_commit_output_encoding();
 
+	if (!is_fixup(command))
+		BUG("not a FIXUP or SQUASH %d", command);
+
 	if (ctx->current_fixup_count > 0) {
 		struct strbuf header = STRBUF_INIT;
 		char *eol;
@@ -2134,8 +2137,7 @@ static int update_squash_messages(struct repository *r,
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
-	} else
-		return error(_("unknown command: %d"), command);
+	}
 	repo_unuse_commit_buffer(r, commit, message);
 
 	if (!res)
diff --git a/t/README b/t/README
index e9ffd9a81c3331..adbbd9acf4ab27 100644
--- a/t/README
+++ b/t/README
@@ -415,6 +415,10 @@ GIT_TEST_PACK_SPARSE=<boolean> if disabled will default the pack-objects
 builtin to use the non-sparse object walk. This can still be overridden by
 the --sparse command-line argument.
 
+GIT_TEST_PACK_PATH_WALK=<boolean> if enabled will default the pack-objects
+builtin to use the path-walk API for the object walk. This can still be
+overridden by the --no-path-walk command-line argument.
+
 GIT_TEST_PRELOAD_INDEX=<boolean> exercises the preload-index code path
 by overriding the minimum number of cache entries required per thread.
 
diff --git a/t/helper/test-path-walk.c b/t/helper/test-path-walk.c
index 61e845e5ec2560..fe63002c2be27d 100644
--- a/t/helper/test-path-walk.c
+++ b/t/helper/test-path-walk.c
@@ -82,6 +82,8 @@ int cmd__path_walk(int argc, const char **argv)
 			 N_("toggle inclusion of tree objects")),
 		OPT_BOOL(0, "prune", &info.prune_all_uninteresting,
 			 N_("toggle pruning of uninteresting paths")),
+		OPT_BOOL(0, "edge-aggressive", &info.edge_aggressive,
+			 N_("toggle aggressive edge walk")),
 		OPT_BOOL(0, "stdin-pl", &stdin_pl,
 			 N_("read a pattern list over stdin")),
 		OPT_END(),
diff --git a/t/meson.build b/t/meson.build
index d052fc3e23d2ec..50e89e764ac3b4 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -51,7 +51,7 @@ clar_unit_tests = executable('unit-tests',
   sources: clar_sources + clar_test_suites,
   dependencies: [libgit_commonmain],
 )
-test('unit-tests', clar_unit_tests)
+test('unit-tests', clar_unit_tests, kwargs: test_kwargs)
 
 unit_test_programs = [
   'unit-tests/t-reftable-basics.c',
@@ -76,7 +76,7 @@ foreach unit_test_program : unit_test_programs
   )
   test(unit_test_name, unit_test,
     workdir: meson.current_source_dir(),
-    timeout: 0,
+    kwargs: test_kwargs,
   )
 endforeach
 
@@ -1212,7 +1212,7 @@ foreach integration_test : integration_tests
     workdir: meson.current_source_dir(),
     env: test_environment,
     depends: test_dependencies + bin_wrappers,
-    timeout: 0,
+    kwargs: test_kwargs,
   )
 endforeach
 
diff --git a/t/perf/p5313-pack-objects.sh b/t/perf/p5313-pack-objects.sh
index 786a2c1c6f5b1a..46a6cd32d24343 100755
--- a/t/perf/p5313-pack-objects.sh
+++ b/t/perf/p5313-pack-objects.sh
@@ -22,46 +22,53 @@ test_expect_success 'create rev input' '
 	EOF
 '
 
-for version in 1 2
-do
-	export version
+test_all_with_args () {
+	parameter=$1
+	export parameter
 
-	test_perf "thin pack with version $version" '
+	test_perf "thin pack with $parameter" '
 		git pack-objects --thin --stdout --revs --sparse \
-			--name-hash-version=$version <in-thin >out
+			$parameter <in-thin >out
 	'
 
-	test_size "thin pack size with version $version" '
+	test_size "thin pack size with $parameter" '
 		test_file_size out
 	'
 
-	test_perf "big pack with version $version" '
+	test_perf "big pack with $parameter" '
 		git pack-objects --stdout --revs --sparse \
-			--name-hash-version=$version <in-big >out
+			$parameter <in-big >out
 	'
 
-	test_size "big pack size with version $version" '
+	test_size "big pack size with $parameter" '
 		test_file_size out
 	'
 
-	test_perf "shallow fetch pack with version $version" '
+	test_perf "shallow fetch pack with $parameter" '
 		git pack-objects --stdout --revs --sparse --shallow \
-			--name-hash-version=$version <in-shallow >out
+			$parameter <in-shallow >out
 	'
 
-	test_size "shallow pack size with version $version" '
+	test_size "shallow pack size with $parameter" '
 		test_file_size out
 	'
 
-	test_perf "repack with version $version" '
-		git repack -adf --name-hash-version=$version
+	test_perf "repack with $parameter" '
+		git repack -adf $parameter
 	'
 
-	test_size "repack size with version $version" '
+	test_size "repack size with $parameter" '
 		gitdir=$(git rev-parse --git-dir) &&
 		pack=$(ls $gitdir/objects/pack/pack-*.pack) &&
 		test_file_size "$pack"
 	'
+}
+
+for version in 1 2
+do
+	test_all_with_args --name-hash-version=$version
 done
 
+test_all_with_args --path-walk
+
 test_done
diff --git a/t/t0000-basic.sh b/t/t0000-basic.sh
index 35c5c2b4f9beb4..2b63e1c86cae30 100755
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@@ -130,7 +130,7 @@ test_expect_success 'subtest: a failing TODO test' '
 '
 
 test_expect_success 'subtest: a passing TODO test' '
-	write_and_run_sub_test_lib_test passing-todo <<-\EOF &&
+	write_and_run_sub_test_lib_test_err passing-todo <<-\EOF &&
 	test_expect_failure "pretend we have fixed a known breakage" "true"
 	test_done
 	EOF
@@ -142,7 +142,7 @@ test_expect_success 'subtest: a passing TODO test' '
 '
 
 test_expect_success 'subtest: 2 TODO tests, one passin' '
-	write_and_run_sub_test_lib_test partially-passing-todos <<-\EOF &&
+	write_and_run_sub_test_lib_test_err partially-passing-todos <<-\EOF &&
 	test_expect_failure "pretend we have a known breakage" "false"
 	test_expect_success "pretend we have a passing test" "true"
 	test_expect_failure "pretend we have fixed another known breakage" "true"
@@ -219,41 +219,44 @@ test_expect_success 'subtest: --verbose option' '
 	test_expect_success "failing test" false
 	test_done
 	EOF
-	mv t1234-verbose/out t1234-verbose/out+ &&
-	grep -v "^Initialized empty" t1234-verbose/out+ >t1234-verbose/out &&
-	check_sub_test_lib_test t1234-verbose <<-\EOF
-	> expecting success of 1234.1 '\''passing test'\'': true
+	mv t1234-verbose/err t1234-verbose/err+ &&
+	grep -v "^Initialized empty" t1234-verbose/err+ >t1234-verbose/err &&
+	check_sub_test_lib_test_err t1234-verbose \
+		<<-\EOF_OUT 3<<-\EOF_ERR
 	> ok 1 - passing test
+	> ok 2 - test with output
+	> not ok 3 - failing test
+	> #	false
+	> # failed 1 among 3 test(s)
+	> 1..3
+	EOF_OUT
+	> expecting success of 1234.1 '\''passing test'\'': true
 	> Z
 	> expecting success of 1234.2 '\''test with output'\'': echo foo
 	> foo
-	> ok 2 - test with output
 	> Z
 	> expecting success of 1234.3 '\''failing test'\'': false
-	> not ok 3 - failing test
-	> #	false
 	> Z
-	> # failed 1 among 3 test(s)
-	> 1..3
-	EOF
+	EOF_ERR
 '
 
 test_expect_success 'subtest: --verbose-only option' '
 	run_sub_test_lib_test_err \
 		t1234-verbose \
 		--verbose-only=2 &&
-	check_sub_test_lib_test t1234-verbose <<-\EOF
+	check_sub_test_lib_test_err t1234-verbose <<-\EOF_OUT 3<<-\EOF_ERR
 	> ok 1 - passing test
-	> Z
-	> expecting success of 1234.2 '\''test with output'\'': echo foo
-	> foo
 	> ok 2 - test with output
-	> Z
 	> not ok 3 - failing test
 	> #	false
 	> # failed 1 among 3 test(s)
 	> 1..3
-	EOF
+	EOF_OUT
+	> Z
+	> expecting success of 1234.2 '\''test with output'\'': echo foo
+	> foo
+	> Z
+	EOF_ERR
 '
 
 test_expect_success 'subtest: skip one with GIT_SKIP_TESTS' '
diff --git a/t/t0050-filesystem.sh b/t/t0050-filesystem.sh
index 5c9dc90d0b096d..ca8568067d31d6 100755
--- a/t/t0050-filesystem.sh
+++ b/t/t0050-filesystem.sh
@@ -10,53 +10,35 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 auml=$(printf '\303\244')
 aumlcdiar=$(printf '\141\314\210')
 
-if test_have_prereq CASE_INSENSITIVE_FS
-then
-	say "will test on a case insensitive filesystem"
-	test_case=test_expect_failure
-else
-	test_case=test_expect_success
-fi
-
 if test_have_prereq UTF8_NFD_TO_NFC
 then
-	say "will test on a unicode corrupting filesystem"
 	test_unicode=test_expect_failure
 else
 	test_unicode=test_expect_success
 fi
 
-test_have_prereq SYMLINKS ||
-	say "will test on a filesystem lacking symbolic links"
-
-if test_have_prereq CASE_INSENSITIVE_FS
-then
-test_expect_success "detection of case insensitive filesystem during repo init" '
+test_expect_success CASE_INSENSITIVE_FS "detection of case insensitive filesystem during repo init" '
 	test $(git config --bool core.ignorecase) = true
 '
-else
-test_expect_success "detection of case insensitive filesystem during repo init" '
+
+test_expect_success !CASE_INSENSITIVE_FS "detection of case insensitive filesystem during repo init" '
 	{
 		test_must_fail git config --bool core.ignorecase >/dev/null ||
 			test $(git config --bool core.ignorecase) = false
 	}
 '
-fi
 
-if test_have_prereq SYMLINKS
-then
-test_expect_success "detection of filesystem w/o symlink support during repo init" '
+test_expect_success SYMLINKS "detection of filesystem w/o symlink support during repo init" '
 	{
 		test_must_fail git config --bool core.symlinks ||
 		test "$(git config --bool core.symlinks)" = true
 	}
 '
-else
-test_expect_success "detection of filesystem w/o symlink support during repo init" '
+
+test_expect_success !SYMLINKS "detection of filesystem w/o symlink support during repo init" '
 	v=$(git config --bool core.symlinks) &&
 	test "$v" = false
 '
-fi
 
 test_expect_success "setup case tests" '
 	git config core.ignorecase true &&
diff --git a/t/t0411-clone-from-partial.sh b/t/t0411-clone-from-partial.sh
index 196fc617843cb9..9e6bca56255be9 100755
--- a/t/t0411-clone-from-partial.sh
+++ b/t/t0411-clone-from-partial.sh
@@ -59,6 +59,12 @@ test_expect_success 'pack-objects should fetch from promisor remote and execute
 
 test_expect_success 'clone from promisor remote does not lazy-fetch by default' '
 	rm -f script-executed &&
+
+	# The --path-walk feature of "git pack-objects" is not
+	# compatible with this kind of fetch from an incomplete repo.
+	GIT_TEST_PACK_PATH_WALK=0 &&
+	export GIT_TEST_PACK_PATH_WALK &&
+
 	test_must_fail git clone evil no-lazy 2>err &&
 	test_grep "lazy fetching disabled" err &&
 	test_path_is_missing script-executed
diff --git a/t/t0450/adoc-help-mismatches b/t/t0450/adoc-help-mismatches
index c4a15fd0cb885a..06b469bdee203d 100644
--- a/t/t0450/adoc-help-mismatches
+++ b/t/t0450/adoc-help-mismatches
@@ -38,7 +38,6 @@ merge-one-file
 multi-pack-index
 name-rev
 notes
-pack-objects
 push
 range-diff
 rebase
diff --git a/t/t1006-cat-file.sh b/t/t1006-cat-file.sh
index 317da6869c88ee..f123ef1e360aca 100755
--- a/t/t1006-cat-file.sh
+++ b/t/t1006-cat-file.sh
@@ -113,53 +113,55 @@ strlen () {
 
 run_tests () {
     type=$1
-    oid=$2
-    size=$3
-    content=$4
-    pretty_content=$5
+    object_name="$2"
+    mode=$3
+    size=$4
+    content=$5
+    pretty_content=$6
+    oid=${7:-"$object_name"}
 
     batch_output="$oid $type $size
 $content"
 
     test_expect_success "$type exists" '
-	git cat-file -e $oid
+	git cat-file -e "$object_name"
     '
 
     test_expect_success "Type of $type is correct" '
 	echo $type >expect &&
-	git cat-file -t $oid >actual &&
+	git cat-file -t "$object_name" >actual &&
 	test_cmp expect actual
     '
 
     test_expect_success "Size of $type is correct" '
 	echo $size >expect &&
-	git cat-file -s $oid >actual &&
+	git cat-file -s "$object_name" >actual &&
 	test_cmp expect actual
     '
 
     test -z "$content" ||
     test_expect_success "Content of $type is correct" '
 	echo_without_newline "$content" >expect &&
-	git cat-file $type $oid >actual &&
+	git cat-file $type "$object_name" >actual &&
 	test_cmp expect actual
     '
 
     test_expect_success "Pretty content of $type is correct" '
 	echo_without_newline "$pretty_content" >expect &&
-	git cat-file -p $oid >actual &&
+	git cat-file -p "$object_name" >actual &&
 	test_cmp expect actual
     '
 
     test -z "$content" ||
     test_expect_success "--batch output of $type is correct" '
 	echo "$batch_output" >expect &&
-	echo $oid | git cat-file --batch >actual &&
+	echo "$object_name" | git cat-file --batch >actual &&
 	test_cmp expect actual
     '
 
     test_expect_success "--batch-check output of $type is correct" '
 	echo "$oid $type $size" >expect &&
-	echo_without_newline $oid | git cat-file --batch-check >actual &&
+	echo_without_newline "$object_name" | git cat-file --batch-check >actual &&
 	test_cmp expect actual
     '
 
@@ -168,13 +170,13 @@ $content"
 	test -z "$content" ||
 		test_expect_success "--batch-command $opt output of $type content is correct" '
 		echo "$batch_output" >expect &&
-		test_write_lines "contents $oid" | git cat-file --batch-command $opt >actual &&
+		test_write_lines "contents $object_name" | git cat-file --batch-command $opt >actual &&
 		test_cmp expect actual
 	'
 
 	test_expect_success "--batch-command $opt output of $type info is correct" '
 		echo "$oid $type $size" >expect &&
-		test_write_lines "info $oid" |
+		test_write_lines "info $object_name" |
 		git cat-file --batch-command $opt >actual &&
 		test_cmp expect actual
 	'
@@ -182,30 +184,45 @@ $content"
 
     test_expect_success "custom --batch-check format" '
 	echo "$type $oid" >expect &&
-	echo $oid | git cat-file --batch-check="%(objecttype) %(objectname)" >actual &&
+	echo "$object_name" | git cat-file --batch-check="%(objecttype) %(objectname)" >actual &&
 	test_cmp expect actual
     '
 
     test_expect_success "custom --batch-command format" '
 	echo "$type $oid" >expect &&
-	echo "info $oid" | git cat-file --batch-command="%(objecttype) %(objectname)" >actual &&
+	echo "info $object_name" | git cat-file --batch-command="%(objecttype) %(objectname)" >actual &&
 	test_cmp expect actual
     '
 
-    test_expect_success '--batch-check with %(rest)' '
+    # FIXME: %(rest) is incompatible with object names that include whitespace,
+    # e.g. HEAD:path/to/a/file with spaces. Use the resolved OID as input to
+    # test this instead of the raw object name.
+    if echo "$object_name" | grep " "; then
+	test_rest=test_expect_failure
+    else
+	test_rest=test_expect_success
+    fi
+
+    $test_rest '--batch-check with %(rest)' '
 	echo "$type this is some extra content" >expect &&
-	echo "$oid    this is some extra content" |
+	echo "$object_name    this is some extra content" |
 		git cat-file --batch-check="%(objecttype) %(rest)" >actual &&
 	test_cmp expect actual
     '
 
+    test_expect_success '--batch-check with %(objectmode)' '
+	echo "$mode $oid" >expect &&
+	echo $object_name | git cat-file --batch-check="%(objectmode) %(objectname)" >actual &&
+	test_cmp expect actual
+    '
+
     test -z "$content" ||
     test_expect_success "--batch without type ($type)" '
 	{
 		echo "$size" &&
 		echo "$content"
 	} >expect &&
-	echo $oid | git cat-file --batch="%(objectsize)" >actual &&
+	echo "$object_name" | git cat-file --batch="%(objectsize)" >actual &&
 	test_cmp expect actual
     '
 
@@ -215,7 +232,7 @@ $content"
 		echo "$type" &&
 		echo "$content"
 	} >expect &&
-	echo $oid | git cat-file --batch="%(objecttype)" >actual &&
+	echo "$object_name" | git cat-file --batch="%(objecttype)" >actual &&
 	test_cmp expect actual
     '
 }
@@ -230,13 +247,14 @@ test_expect_success "setup" '
 	git config extensions.compatobjectformat $test_compat_hash_algo &&
 	echo_without_newline "$hello_content" > hello &&
 	git update-index --add hello &&
+	echo_without_newline "$hello_content" > "path with spaces" &&
+	git update-index --add --chmod=+x "path with spaces" &&
 	git commit -m "add hello file"
 '
 
 run_blob_tests () {
     oid=$1
-
-    run_tests 'blob' $oid $hello_size "$hello_content" "$hello_content"
+    run_tests 'blob' $oid "" $hello_size "$hello_content" "$hello_content"
 
     test_expect_success '--batch-command --buffer with flush for blob info' '
 	echo "$oid blob $hello_size" >expect &&
@@ -269,13 +287,17 @@ test_expect_success '--batch-check without %(rest) considers whole line' '
 
 tree_oid=$(git write-tree)
 tree_compat_oid=$(git rev-parse --output-object-format=$test_compat_hash_algo $tree_oid)
-tree_size=$(($(test_oid rawsz) + 13))
-tree_compat_size=$(($(test_oid --hash=compat rawsz) + 13))
-tree_pretty_content="100644 blob $hello_oid	hello${LF}"
-tree_compat_pretty_content="100644 blob $hello_compat_oid	hello${LF}"
-
-run_tests 'tree' $tree_oid $tree_size "" "$tree_pretty_content"
-run_tests 'tree' $tree_compat_oid $tree_compat_size "" "$tree_compat_pretty_content"
+tree_size=$((2 * $(test_oid rawsz) + 13 + 24))
+tree_compat_size=$((2 * $(test_oid --hash=compat rawsz) + 13 + 24))
+tree_pretty_content="100644 blob $hello_oid	hello${LF}100755 blob $hello_oid	path with spaces${LF}"
+tree_compat_pretty_content="100644 blob $hello_compat_oid	hello${LF}100755 blob $hello_compat_oid	path with spaces${LF}"
+
+run_tests 'tree' $tree_oid "" $tree_size "" "$tree_pretty_content"
+run_tests 'tree' $tree_compat_oid "" $tree_compat_size "" "$tree_compat_pretty_content"
+run_tests 'blob' "$tree_oid:hello" "100644" $hello_size "" "$hello_content" $hello_oid
+run_tests 'blob' "$tree_compat_oid:hello" "100644" $hello_size "" "$hello_content" $hello_compat_oid
+run_tests 'blob' "$tree_oid:path with spaces" "100755" $hello_size "" "$hello_content" $hello_oid
+run_tests 'blob' "$tree_compat_oid:path with spaces" "100755" $hello_size "" "$hello_content" $hello_compat_oid
 
 commit_message="Initial commit"
 commit_oid=$(echo_without_newline "$commit_message" | git commit-tree $tree_oid)
@@ -294,8 +316,8 @@ committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
 
 $commit_message"
 
-run_tests 'commit' $commit_oid $commit_size "$commit_content" "$commit_content"
-run_tests 'commit' $commit_compat_oid $commit_compat_size "$commit_compat_content" "$commit_compat_content"
+run_tests 'commit' $commit_oid "" $commit_size "$commit_content" "$commit_content"
+run_tests 'commit' $commit_compat_oid "" $commit_compat_size "$commit_compat_content" "$commit_compat_content"
 
 tag_header_without_oid="type blob
 tag hellotag
@@ -318,8 +340,8 @@ tag_size=$(strlen "$tag_content")
 tag_compat_oid=$(git rev-parse --output-object-format=$test_compat_hash_algo $tag_oid)
 tag_compat_size=$(strlen "$tag_compat_content")
 
-run_tests 'tag' $tag_oid $tag_size "$tag_content" "$tag_content"
-run_tests 'tag' $tag_compat_oid $tag_compat_size "$tag_compat_content" "$tag_compat_content"
+run_tests 'tag' $tag_oid "" $tag_size "$tag_content" "$tag_content"
+run_tests 'tag' $tag_compat_oid "" $tag_compat_size "$tag_compat_content" "$tag_compat_content"
 
 test_expect_success "Reach a blob from a tag pointing to it" '
 	echo_without_newline "$hello_content" >expect &&
@@ -1198,6 +1220,31 @@ test_expect_success 'cat-file --batch-check respects replace objects' '
 	test_cmp expect actual
 '
 
+test_expect_success 'batch-check with a submodule' '
+	# FIXME: this call to mktree is incompatible with compatObjectFormat
+	# because the submodule OID cannot be mapped to the compat hash algo.
+	test_unconfig extensions.compatobjectformat &&
+	printf "160000 commit $(test_oid deadbeef)\tsub\n" >tree-with-sub &&
+	tree=$(git mktree <tree-with-sub) &&
+	test_config extensions.compatobjectformat $test_compat_hash_algo &&
+
+	git cat-file --batch-check >actual <<-EOF &&
+	$tree:sub
+	EOF
+	printf "$(test_oid deadbeef) submodule\n" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'batch-check with a submodule, object exists' '
+	printf "160000 commit $commit_oid\tsub\n" >tree-with-sub &&
+	tree=$(git mktree <tree-with-sub) &&
+	git cat-file --batch-check >actual <<-EOF &&
+	$tree:sub
+	EOF
+	printf "$commit_oid commit $commit_size\n" >expect &&
+	test_cmp expect actual
+'
+
 # Pull the entry for object with oid "$1" out of the output of
 # "cat-file --batch", including its object content (which requires
 # parsing and reading a set amount of bytes, hence perl).
diff --git a/t/t1007-hash-object.sh b/t/t1007-hash-object.sh
index dbbe9fb0d4b19b..64658b3ba52e4f 100755
--- a/t/t1007-hash-object.sh
+++ b/t/t1007-hash-object.sh
@@ -30,7 +30,7 @@ setup_repo() {
 
 test_repo=test
 push_repo() {
-	test_create_repo $test_repo
+	git init --quiet $test_repo
 	cd $test_repo
 
 	setup_repo
diff --git a/t/t3600-rm.sh b/t/t3600-rm.sh
index 98259e2adaa9db..1f16e6b52285bc 100755
--- a/t/t3600-rm.sh
+++ b/t/t3600-rm.sh
@@ -17,11 +17,6 @@ test_expect_success 'Initialize test directory' '
 	git commit -m "add normal files"
 '
 
-if test_have_prereq !FUNNYNAMES
-then
-	say 'Your filesystem does not allow tabs in filenames.'
-fi
-
 test_expect_success FUNNYNAMES 'add files with funny names' '
 	touch -- "tab	embedded" "newline${LF}embedded" &&
 	git add -- "tab	embedded" "newline${LF}embedded" &&
diff --git a/t/t4000-diff-format.sh b/t/t4000-diff-format.sh
index a51f881b1c9ee0..32b14e3a714b0b 100755
--- a/t/t4000-diff-format.sh
+++ b/t/t4000-diff-format.sh
@@ -36,7 +36,7 @@ test_expect_success 'git diff-files -p after editing work tree.' '
 # that's as far as it comes
 if [ "$(git config --get core.filemode)" = false ]
 then
-	say 'filemode disabled on the filesystem'
+	skip_all='filemode disabled on the filesystem'
 	test_done
 fi
 
diff --git a/t/t4018/r-indent b/t/t4018/r-indent
new file mode 100644
index 00000000000000..9df440f2a4999a
--- /dev/null
+++ b/t/t4018/r-indent
@@ -0,0 +1,6 @@
+RIGHT <- function(a, b) {
+    c = mean(a, b)
+    d = c + 2
+    ChangeMe()
+    return (d)
+}
diff --git a/t/t4018/r-indent-nested b/t/t4018/r-indent-nested
new file mode 100644
index 00000000000000..30412e6c79ca7e
--- /dev/null
+++ b/t/t4018/r-indent-nested
@@ -0,0 +1,10 @@
+LEFT = function(a, b) {
+    c = mean(a, b)
+    RIGHT = function(d, e) {
+        f = var(d, e)
+        g = f + 1
+        ChangeMe()
+        return (g)
+    }
+    return (RIGHT(2, 3))
+}
diff --git a/t/t4018/r-noindent b/t/t4018/r-noindent
new file mode 100644
index 00000000000000..6d9b01ffe3d305
--- /dev/null
+++ b/t/t4018/r-noindent
@@ -0,0 +1,6 @@
+RIGHT <- function(a, b) {
+c = mean(a, b)
+d = c + 2
+ChangeMe()
+return (c)
+}
diff --git a/t/t4041-diff-submodule-option.sh b/t/t4041-diff-submodule-option.sh
index 28f9d83d4c1c34..4d4aa1650fe84a 100755
--- a/t/t4041-diff-submodule-option.sh
+++ b/t/t4041-diff-submodule-option.sh
@@ -48,11 +48,12 @@ commit_file () {
 	git commit "$@" -m "Commit $*" >/dev/null
 }
 
-test_create_repo sm1 &&
-add_file . foo >/dev/null
-
-head1=$(add_file sm1 foo1 foo2)
-fullhead1=$(cd sm1; git rev-parse --verify HEAD)
+test_expect_success 'setup submodule' '
+	git init sm1 &&
+	add_file . foo &&
+	head1=$(add_file sm1 foo1 foo2) &&
+	fullhead1=$(cd sm1 && git rev-parse --verify HEAD)
+'
 
 test_expect_success 'added submodule' '
 	git add sm1 &&
@@ -235,10 +236,13 @@ test_expect_success 'typechanged submodule(submodule->blob)' '
 	test_cmp expected actual
 '
 
-rm -f sm1 &&
-test_create_repo sm1 &&
-head6=$(add_file sm1 foo6 foo7)
-fullhead6=$(cd sm1; git rev-parse --verify HEAD)
+test_expect_success 'setup submodule anew' '
+	rm -f sm1 &&
+	git init sm1 &&
+	head6=$(add_file sm1 foo6 foo7) &&
+	fullhead6=$(cd sm1 && git rev-parse --verify HEAD)
+'
+
 test_expect_success 'nonexistent commit' '
 	git diff-index -p --submodule=log HEAD >actual &&
 	cat >expected <<-EOF &&
diff --git a/t/t4053-diff-no-index.sh b/t/t4053-diff-no-index.sh
index 5e5bad61ca1ed8..01db9243abfe4f 100755
--- a/t/t4053-diff-no-index.sh
+++ b/t/t4053-diff-no-index.sh
@@ -295,4 +295,79 @@ test_expect_success PIPE,SYMLINKS 'diff --no-index reads from pipes' '
 	test_cmp expect actual
 '
 
+test_expect_success 'diff --no-index F F rejects pathspecs' '
+	test_must_fail git diff --no-index -- a/1 a/2 a 2>actual.err &&
+	test_grep "usage: git diff --no-index" actual.err
+'
+
+test_expect_success 'diff --no-index D F rejects pathspecs' '
+	test_must_fail git diff --no-index -- a a/2 a 2>actual.err &&
+	test_grep "usage: git diff --no-index" actual.err
+'
+
+test_expect_success 'diff --no-index F D rejects pathspecs' '
+	test_must_fail git diff --no-index -- a/1 b b 2>actual.err &&
+	test_grep "usage: git diff --no-index" actual.err
+'
+
+test_expect_success 'diff --no-index rejects absolute pathspec' '
+	test_must_fail git diff --no-index -- a b $(pwd)/a/1
+'
+
+test_expect_success 'diff --no-index with pathspec' '
+	test_expect_code 1 git diff --name-status --no-index a b 1 >actual &&
+	cat >expect <<-EOF &&
+	D	a/1
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'diff --no-index with pathspec no matches' '
+	test_expect_code 0 git diff --name-status --no-index a b missing
+'
+
+test_expect_success 'diff --no-index with negative pathspec' '
+	test_expect_code 1 git diff --name-status --no-index a b ":!2" >actual &&
+	cat >expect <<-EOF &&
+	D	a/1
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'setup nested' '
+	mkdir -p c/1/2 &&
+	mkdir -p d/1/2 &&
+	echo 1 >c/1/2/a &&
+	echo 2 >c/1/2/b
+'
+
+test_expect_success 'diff --no-index with pathspec nested negative pathspec' '
+	test_expect_code 0 git diff --no-index c d ":!1"
+'
+
+test_expect_success 'diff --no-index with pathspec nested pathspec' '
+	test_expect_code 1 git diff --name-status --no-index c d 1/2 >actual &&
+	cat >expect <<-EOF &&
+	D	c/1/2/a
+	D	c/1/2/b
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'diff --no-index with pathspec glob' '
+	test_expect_code 1 git diff --name-status --no-index c d ":(glob)**/a" >actual &&
+	cat >expect <<-EOF &&
+	D	c/1/2/a
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'diff --no-index with pathspec glob and exclude' '
+	test_expect_code 1 git diff --name-status --no-index c d ":(glob,exclude)**/a" >actual &&
+	cat >expect <<-EOF &&
+	D	c/1/2/b
+	EOF
+	test_cmp expect actual
+'
+
 test_done
diff --git a/t/t4060-diff-submodule-option-diff-format.sh b/t/t4060-diff-submodule-option-diff-format.sh
index 76b83101d3b7b6..dbfeb7470bcfad 100755
--- a/t/t4060-diff-submodule-option-diff-format.sh
+++ b/t/t4060-diff-submodule-option-diff-format.sh
@@ -363,9 +363,12 @@ test_expect_success 'typechanged submodule(submodule->blob)' '
 	diff_cmp expected actual
 '
 
-rm -f sm1 &&
-test_create_repo sm1 &&
-head6=$(add_file sm1 foo6 foo7)
+test_expect_success 'setup' '
+	rm -f sm1 &&
+	git init sm1 &&
+	head6=$(add_file sm1 foo6 foo7)
+'
+
 test_expect_success 'nonexistent commit' '
 	git diff-index -p --submodule=diff HEAD >actual &&
 	cat >expected <<-EOF &&
diff --git a/t/t5300-pack-object.sh b/t/t5300-pack-object.sh
index a5932b6a8be0ac..ae72158b94bdbc 100755
--- a/t/t5300-pack-object.sh
+++ b/t/t5300-pack-object.sh
@@ -723,4 +723,23 @@ test_expect_success '--name-hash-version=2 and --write-bitmap-index are incompat
 	! test_grep "currently, --write-bitmap-index requires --name-hash-version=1" err
 '
 
+test_expect_success '--path-walk pack everything' '
+	git -C server rev-parse HEAD >in &&
+	GIT_PROGRESS_DELAY=0 git -C server pack-objects \
+		--stdout --revs --path-walk --progress <in >out.pack 2>err &&
+	grep "Compressing objects by path" err &&
+	git -C server index-pack --stdin <out.pack
+'
+
+test_expect_success '--path-walk thin pack' '
+	cat >in <<-EOF &&
+	$(git -C server rev-parse HEAD)
+	^$(git -C server rev-parse HEAD~2)
+	EOF
+	GIT_PROGRESS_DELAY=0 git -C server pack-objects \
+		--thin --stdout --revs --path-walk --progress <in >out.pack 2>err &&
+	grep "Compressing objects by path" err &&
+	git -C server index-pack --fix-thin --stdin <out.pack
+'
+
 test_done
diff --git a/t/t5306-pack-nobase.sh b/t/t5306-pack-nobase.sh
index 805d60ff3179ce..609399d54fbb5b 100755
--- a/t/t5306-pack-nobase.sh
+++ b/t/t5306-pack-nobase.sh
@@ -59,6 +59,11 @@ test_expect_success 'indirectly clone patch_clone' '
 	 git pull ../.git &&
 	 test $(git rev-parse HEAD) = $B &&
 
+	# The --path-walk feature of "git pack-objects" is not
+	# compatible with this kind of fetch from an incomplete repo.
+	GIT_TEST_PACK_PATH_WALK=0 &&
+	export GIT_TEST_PACK_PATH_WALK &&
+
 	 git pull ../patch_clone/.git &&
 	 test $(git rev-parse HEAD) = $C
 	)
diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
index a62b463eaf0932..b6926f10270812 100755
--- a/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh
@@ -158,8 +158,9 @@ test_bitmap_cases () {
 		ls .git/objects/pack/ | grep bitmap >output &&
 		test_line_count = 1 output &&
 		# verify equivalent packs are generated with/without using bitmap index
-		packasha1=$(git pack-objects --no-use-bitmap-index --all packa </dev/null) &&
-		packbsha1=$(git pack-objects --use-bitmap-index --all packb </dev/null) &&
+		# Be careful to not use the path-walk option in either case.
+		packasha1=$(git pack-objects --no-use-bitmap-index --no-path-walk --all packa </dev/null) &&
+		packbsha1=$(git pack-objects --use-bitmap-index --no-path-walk --all packb </dev/null) &&
 		list_packed_objects packa-$packasha1.idx >packa.objects &&
 		list_packed_objects packb-$packbsha1.idx >packb.objects &&
 		test_cmp packa.objects packb.objects
@@ -388,6 +389,14 @@ test_bitmap_cases () {
 		git init --bare client.git &&
 		(
 			cd client.git &&
+
+			# This test relies on reusing a delta, but if the
+			# path-walk machinery is engaged, the base object
+			# is considered too small to use during the
+			# dynamic computation, so is not used.
+			GIT_TEST_PACK_PATH_WALK=0 &&
+			export GIT_TEST_PACK_PATH_WALK &&
+
 			git config transfer.unpackLimit 1 &&
 			git fetch .. delta-reuse-old:delta-reuse-old &&
 			git fetch .. delta-reuse-new:delta-reuse-new &&
diff --git a/t/t5316-pack-delta-depth.sh b/t/t5316-pack-delta-depth.sh
index defaa06d650470..03dfb7a61ea978 100755
--- a/t/t5316-pack-delta-depth.sh
+++ b/t/t5316-pack-delta-depth.sh
@@ -89,15 +89,18 @@ max_chain() {
 # adjusted (or scrapped if the heuristics have become too unreliable)
 test_expect_success 'packing produces a long delta' '
 	# Use --window=0 to make sure we are seeing reused deltas,
-	# not computing a new long chain.
-	pack=$(git pack-objects --all --window=0 </dev/null pack) &&
+	# not computing a new long chain. (Also avoid the --path-walk
+	# option as it may break delta chains.)
+	pack=$(git pack-objects --all --window=0 --no-path-walk </dev/null pack) &&
 	echo 9 >expect &&
 	max_chain pack-$pack.pack >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success '--depth limits depth' '
-	pack=$(git pack-objects --all --depth=5 </dev/null pack) &&
+	# Avoid --path-walk to avoid breaking delta chains across path
+	# boundaries.
+	pack=$(git pack-objects --all --depth=5 --no-path-walk </dev/null pack) &&
 	echo 5 >expect &&
 	max_chain pack-$pack.pack >actual &&
 	test_cmp expect actual
diff --git a/t/t5332-multi-pack-reuse.sh b/t/t5332-multi-pack-reuse.sh
index 57cad7708f80f9..395d09444ced72 100755
--- a/t/t5332-multi-pack-reuse.sh
+++ b/t/t5332-multi-pack-reuse.sh
@@ -7,6 +7,13 @@ test_description='pack-objects multi-pack reuse'
 
 GIT_TEST_MULTI_PACK_INDEX=0
 GIT_TEST_MULTI_PACK_INDEX_WRITE_INCREMENTAL=0
+
+# The --path-walk option does not consider the preferred pack
+# at all for reusing deltas, so this variable changes the
+# behavior of this test, if enabled.
+GIT_TEST_PACK_PATH_WALK=0
+export GIT_TEST_PACK_PATH_WALK
+
 objdir=.git/objects
 packdir=$objdir/pack
 
diff --git a/t/t5516-fetch-push.sh b/t/t5516-fetch-push.sh
index dabcc5f8117645..782f5f93ea03ae 100755
--- a/t/t5516-fetch-push.sh
+++ b/t/t5516-fetch-push.sh
@@ -1909,4 +1909,14 @@ test_expect_success 'push with config push.useBitmaps' '
 		--thin --delta-base-offset -q --no-use-bitmap-index <false
 '
 
+test_expect_success 'push with config pack.usePathWalk=true' '
+	mk_test testrepo heads/main &&
+	git checkout main &&
+	test_config pack.usePathWalk true &&
+	GIT_TRACE2_EVENT="$(pwd)/path-walk.txt" \
+	git push --quiet testrepo main:test &&
+
+	test_region pack-objects path-walk path-walk.txt
+'
+
 test_done
diff --git a/t/t5538-push-shallow.sh b/t/t5538-push-shallow.sh
index e91fcc173e8116..dc0e972943a6f6 100755
--- a/t/t5538-push-shallow.sh
+++ b/t/t5538-push-shallow.sh
@@ -123,4 +123,45 @@ EOF
 	git cat-file blob $(echo 1|git hash-object --stdin) >/dev/null
 	)
 '
+
+test_expect_success 'push new commit from shallow clone has correct object count' '
+	git init origin &&
+	test_commit -C origin a &&
+	test_commit -C origin b &&
+
+	git clone --depth=1 "file://$(pwd)/origin" client &&
+	git -C client checkout -b topic &&
+	git -C client commit --allow-empty -m "empty" &&
+	GIT_PROGRESS_DELAY=0 git -C client push --progress origin topic 2>err &&
+	test_grep "Enumerating objects: 1, done." err
+'
+
+test_expect_success 'push new commit from shallow clone has good deltas' '
+	git init base &&
+	test_seq 1 999 >base/a &&
+	test_commit -C base initial &&
+	git -C base add a &&
+	git -C base commit -m "big a" &&
+
+	git clone --depth=1 "file://$(pwd)/base" deltas &&
+	git -C deltas checkout -b deltas &&
+	test_seq 1 1000 >deltas/a &&
+	git -C deltas commit -a -m "bigger a" &&
+	GIT_PROGRESS_DELAY=0 git -C deltas push --progress origin deltas 2>err &&
+
+	test_grep "Enumerating objects: 5, done" err &&
+
+	# If the delta base is found, then this message uses "bytes".
+	# If the delta base is not found, then this message uses "KiB".
+	test_grep "Writing objects: .* bytes" err &&
+
+	git -C deltas commit --amend -m "changed message" &&
+	GIT_TRACE2_EVENT="$(pwd)/config-push.txt" \
+	GIT_PROGRESS_DELAY=0 git -C deltas -c pack.usePathWalk=true \
+		push --progress -f origin deltas 2>err &&
+
+	test_grep "Enumerating objects: 1, done" err &&
+	test_region pack-objects path-walk config-push.txt
+'
+
 test_done
diff --git a/t/t6601-path-walk.sh b/t/t6601-path-walk.sh
index 8d187f7279c4de..56bd1e3c5bec97 100755
--- a/t/t6601-path-walk.sh
+++ b/t/t6601-path-walk.sh
@@ -376,6 +376,26 @@ test_expect_success 'topic, not base, boundary with pruning' '
 	test_cmp_sorted expect out
 '
 
+test_expect_success 'topic, not base, --edge-aggressive with pruning' '
+	test-tool path-walk --prune --edge-aggressive -- topic --not base >out &&
+
+	cat >expect <<-EOF &&
+	0:commit::$(git rev-parse topic)
+	1:tree::$(git rev-parse topic^{tree})
+	1:tree::$(git rev-parse base^{tree}):UNINTERESTING
+	2:tree:right/:$(git rev-parse topic:right)
+	2:tree:right/:$(git rev-parse base:right):UNINTERESTING
+	3:blob:right/c:$(git rev-parse base:right/c):UNINTERESTING
+	3:blob:right/c:$(git rev-parse topic:right/c)
+	blobs:2
+	commits:1
+	tags:0
+	trees:4
+	EOF
+
+	test_cmp_sorted expect out
+'
+
 test_expect_success 'trees are reported exactly once' '
 	test_when_finished "rm -rf unique-trees" &&
 	test_create_repo unique-trees &&
diff --git a/t/t7401-submodule-summary.sh b/t/t7401-submodule-summary.sh
index 9c3cc4cf4046be..66c3ec2da22800 100755
--- a/t/t7401-submodule-summary.sh
+++ b/t/t7401-submodule-summary.sh
@@ -38,10 +38,11 @@ commit_file () {
 	git commit "$@" -m "Commit $*" >/dev/null
 }
 
-test_create_repo sm1 &&
-add_file . foo >/dev/null
-
-head1=$(add_file sm1 foo1 foo2)
+test_expect_success 'setup submodule' '
+	git init sm1 &&
+	add_file . foo &&
+	head1=$(add_file sm1 foo1 foo2)
+'
 
 test_expect_success 'added submodule' "
 	git add sm1 &&
@@ -214,9 +215,12 @@ test_expect_success 'typechanged submodule(submodule->blob)' "
 	test_cmp expected actual
 "
 
-rm -f sm1 &&
-test_create_repo sm1 &&
-head6=$(add_file sm1 foo6 foo7)
+test_expect_success 'setup submodule' '
+	rm -f sm1 &&
+	git init sm1 &&
+	head6=$(add_file sm1 foo6 foo7)
+'
+
 test_expect_success 'nonexistent commit' "
 	git submodule summary >actual &&
 	cat >expected <<-EOF &&
diff --git a/t/t7406-submodule-update.sh b/t/t7406-submodule-update.sh
index c562bad042ab2d..ab76d4b6dc41b8 100755
--- a/t/t7406-submodule-update.sh
+++ b/t/t7406-submodule-update.sh
@@ -1095,12 +1095,15 @@ test_expect_success 'submodule update --quiet passes quietness to fetch with a s
 	(cd super5 &&
 	 # This test var can mess with the stderr output checked in this test.
 	 GIT_TEST_NAME_HASH_VERSION=1 \
+	 GIT_TEST_PACK_PATH_WALK=0 \
 		git submodule update --quiet --init --depth=1 submodule3 >out 2>err &&
 	 test_must_be_empty out &&
 	 test_must_be_empty err
 	) &&
 	git clone super4 super6 &&
 	(cd super6 &&
+	 # This test variable will create a "warning" message to stderr
+	 GIT_TEST_PACK_PATH_WALK=0 \
 	 git submodule update --init --depth=1 submodule3 >out 2>err &&
 	 test_file_not_empty out &&
 	 test_file_not_empty err
diff --git a/t/t7815-grep-binary.sh b/t/t7815-grep-binary.sh
index b7d83f9a5deac2..55d5e6de17cf94 100755
--- a/t/t7815-grep-binary.sh
+++ b/t/t7815-grep-binary.sh
@@ -63,7 +63,7 @@ test_expect_success 'git grep ile a' '
 	git grep ile a
 '
 
-test_expect_failure !CYGWIN 'git grep .fi a' '
+test_expect_failure !CYGWIN,!MACOS 'git grep .fi a' '
 	git grep .fi a
 '
 
diff --git a/t/t9500-gitweb-standalone-no-errors.sh b/t/t9500-gitweb-standalone-no-errors.sh
index 7679780fb87b4f..578d6c8b329358 100755
--- a/t/t9500-gitweb-standalone-no-errors.sh
+++ b/t/t9500-gitweb-standalone-no-errors.sh
@@ -700,19 +700,17 @@ test_expect_success \
 # ----------------------------------------------------------------------
 # syntax highlighting
 
+test_lazy_prereq HIGHLIGHT '
+	highlight_version=$(highlight --version </dev/null 2>/dev/null) &&
+	test -n "$highlight_version"
+'
 
-highlight_version=$(highlight --version </dev/null 2>/dev/null)
-if [ $? -eq 127 ]; then
-	say "Skipping syntax highlighting tests: 'highlight' not found"
-elif test -z "$highlight_version"; then
-	say "Skipping syntax highlighting tests: incorrect 'highlight' found"
-else
-	test_set_prereq HIGHLIGHT
+test_expect_success HIGHLIGHT '
 	cat >>gitweb_config.perl <<-\EOF
 	our $highlight_bin = "highlight";
-	$feature{'highlight'}{'override'} = 1;
+	$feature{"highlight"}{"override"} = 1;
 	EOF
-fi
+'
 
 test_expect_success HIGHLIGHT \
 	'syntax highlighting (no highlight, unknown syntax)' \
diff --git a/t/t9822-git-p4-path-encoding.sh b/t/t9822-git-p4-path-encoding.sh
index 572d395498e30a..e6e07facd4b718 100755
--- a/t/t9822-git-p4-path-encoding.sh
+++ b/t/t9822-git-p4-path-encoding.sh
@@ -7,12 +7,17 @@ test_description='Clone repositories with non ASCII paths'
 UTF8_ESCAPED="a-\303\244_o-\303\266_u-\303\274.txt"
 ISO8859_ESCAPED="a-\344_o-\366_u-\374.txt"
 
-ISO8859="$(printf "$ISO8859_ESCAPED")" &&
-echo content123 >"$ISO8859" &&
-rm "$ISO8859" || {
+test_lazy_prereq FS_ACCEPTS_ISO_8859_1 '
+	ISO8859="$(printf "$ISO8859_ESCAPED")" &&
+	echo content123 >"$ISO8859" &&
+	rm "$ISO8859"
+'
+
+if ! test_have_prereq FS_ACCEPTS_ISO_8859_1
+then
 	skip_all="fs does not accept ISO-8859-1 filenames"
 	test_done
-}
+fi
 
 test_expect_success 'start p4d' '
 	start_p4d
diff --git a/t/t9835-git-p4-metadata-encoding-python2.sh b/t/t9835-git-p4-metadata-encoding-python2.sh
index 6116f806f63115..b969c7e0d5aef6 100755
--- a/t/t9835-git-p4-metadata-encoding-python2.sh
+++ b/t/t9835-git-p4-metadata-encoding-python2.sh
@@ -12,23 +12,25 @@ failing, and produces maximally sane output in git.'
 ## SECTION REPEATED IN t9836 ##
 ###############################
 
+EXTRA_PATH="$(pwd)/temp_python"
+mkdir "$EXTRA_PATH"
+PATH="$EXTRA_PATH:$PATH"
+export PATH
+
 # These tests are specific to Python 2. Write a custom script that executes
 # git-p4 directly with the Python 2 interpreter to ensure that we use that
 # version even if Git was compiled with Python 3.
-python_target_binary=$(which python2)
-if test -n "$python_target_binary"
-then
-	mkdir temp_python
-	PATH="$(pwd)/temp_python:$PATH"
-	export PATH
-
-	write_script temp_python/git-p4-python2 <<-EOF
+test_lazy_prereq P4_PYTHON2 '
+	python_target_binary=$(which python2) &&
+	test -n "$python_target_binary" &&
+	write_script "$EXTRA_PATH"/git-p4-python2 <<-EOF &&
 	exec "$python_target_binary" "$(git --exec-path)/git-p4" "\$@"
 	EOF
-fi
+	( git p4-python2 || true ) >err &&
+	test_grep "valid commands" err
+'
 
-git p4-python2 >err
-if ! grep 'valid commands' err
+if ! test_have_prereq P4_PYTHON2
 then
 	skip_all="skipping python2 git p4 tests; python2 not available"
 	test_done
diff --git a/t/t9836-git-p4-metadata-encoding-python3.sh b/t/t9836-git-p4-metadata-encoding-python3.sh
index 5e5217a66b4fdb..da6669bf7119e5 100755
--- a/t/t9836-git-p4-metadata-encoding-python3.sh
+++ b/t/t9836-git-p4-metadata-encoding-python3.sh
@@ -12,23 +12,25 @@ failing, and produces maximally sane output in git.'
 ## SECTION REPEATED IN t9835 ##
 ###############################
 
+EXTRA_PATH="$(pwd)/temp_python"
+mkdir "$EXTRA_PATH"
+PATH="$EXTRA_PATH:$PATH"
+export PATH
+
 # These tests are specific to Python 3. Write a custom script that executes
 # git-p4 directly with the Python 3 interpreter to ensure that we use that
 # version even if Git was compiled with Python 2.
-python_target_binary=$(which python3)
-if test -n "$python_target_binary"
-then
-	mkdir temp_python
-	PATH="$(pwd)/temp_python:$PATH"
-	export PATH
-
-	write_script temp_python/git-p4-python3 <<-EOF
+test_lazy_prereq P4_PYTHON3 '
+	python_target_binary=$(which python3) &&
+	test -n "$python_target_binary" &&
+	write_script "$EXTRA_PATH"/git-p4-python3 <<-EOF &&
 	exec "$python_target_binary" "$(git --exec-path)/git-p4" "\$@"
 	EOF
-fi
+	( git p4-python3 || true ) >err &&
+	test_grep "valid commands" err
+'
 
-git p4-python3 >err
-if ! grep 'valid commands' err
+if ! test_have_prereq P4_PYTHON3
 then
 	skip_all="skipping python3 git p4 tests; python3 not available"
 	test_done
diff --git a/t/t9903-bash-prompt.sh b/t/t9903-bash-prompt.sh
index d667dda654e2de..637a6f13a6d9b3 100755
--- a/t/t9903-bash-prompt.sh
+++ b/t/t9903-bash-prompt.sh
@@ -66,10 +66,6 @@ test_expect_success 'prompt - unborn branch' '
 	test_cmp expected "$actual"
 '
 
-if test_have_prereq !FUNNYNAMES; then
-	say 'Your filesystem does not allow newlines in filenames.'
-fi
-
 test_expect_success FUNNYNAMES 'prompt - with newline in path' '
     repo_with_newline="repo
 with
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 92d0db13d7429d..9ffcae0472e1a3 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -470,7 +470,7 @@ then
 	then
 		: Executed by a Bash version supporting BASH_XTRACEFD.  Good.
 	else
-		echo >&2 "warning: ignoring -x; '$0' is untraceable without BASH_XTRACEFD"
+		echo >&2 "# warning: ignoring -x; '$0' is untraceable without BASH_XTRACEFD"
 		trace=
 	fi
 fi
@@ -707,7 +707,7 @@ then
 	exec 3>>"$GIT_TEST_TEE_OUTPUT_FILE" 4>&3
 elif test "$verbose" = "t"
 then
-	exec 4>&2 3>&1
+	exec 4>&2 3>&2
 else
 	exec 4>/dev/null 3>/dev/null
 fi
@@ -949,7 +949,7 @@ maybe_setup_verbose () {
 	test -z "$verbose_only" && return
 	if match_pattern_list $test_count "$verbose_only"
 	then
-		exec 4>&2 3>&1
+		exec 4>&2 3>&2
 		# Emit a delimiting blank line when going from
 		# non-verbose to verbose.  Within verbose mode the
 		# delimiter is printed by test_expect_*.  The choice
@@ -1272,7 +1272,14 @@ test_done () {
 
 		check_test_results_san_file_ "$test_failure"
 
-		if test -z "$skip_all" && test -n "$invert_exit_code"
+		if test "$test_fixed" != 0
+		then
+			if test -z "$invert_exit_code"
+			then
+				GIT_EXIT_OK=t
+				exit 1
+			fi
+		elif test -z "$skip_all" && test -n "$invert_exit_code"
 		then
 			say_color warn "# faking up non-zero exit with --invert-exit-code"
 			GIT_EXIT_OK=t
@@ -1638,6 +1645,9 @@ fi
 # Fix some commands on Windows, and other OS-specific things
 uname_s=$(uname -s)
 case $uname_s in
+Darwin)
+	test_set_prereq MACOS
+	;;
 *MINGW*)
 	# Windows has its own (incompatible) sort and find
 	sort () {
diff --git a/userdiff.c b/userdiff.c
index 05776ccd10401c..fe710a68bfdfa6 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -327,6 +327,10 @@ PATTERNS("python",
 	 "|[-+0-9.e]+[jJlL]?|0[xX]?[0-9a-fA-F]+[lL]?"
 	 "|[-+*/<>%&^|=!]=|//=?|<<=?|>>=?|\\*\\*=?"),
 	 /* -- */
+PATTERNS("r",
+	"^[ \t]*([a-zA-z][a-zA-Z0-9_.]*[ \t]*(<-|=)[ \t]*function.*)$",
+	/* -- */
+	"[^ \t]+"),
 PATTERNS("ruby",
 	 "^[ \t]*((class|module|def)[ \t].*)$",
 	 /* -- */