Extract shared fmt module, expand tests to 47, clean up codebase

Refactor:
- New src/fmt.zig: shared diff callbacks (compactCallback, humanCallback),
  stat summary (writeStat), and date formatting (epochToDate). Eliminates
  ~200 lines of duplication between diff.zig and show.zig.
- Fixes subtle color guard inconsistency in show.zig's human callback
  (bare if vs if/else blocks).
- Remove dead code: unused last_file field, unused color constants
  (blue, magenta, white, bg_red, bg_green), redundant default_count.
- Clean up cli.zig: remove unused writer param from openRepo, hoist
  repo open above command dispatch.

New tests (47 total, up from 34):
- show --stat: delete-only commit, additions-only commit, totals consistency
- Merge commits: log and show on merge
- Multi-file diffs: file listing and count
- Subdirectory: status/log/diff from within a subdirectory
- Usage: no args, --help, help all show usage text

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: fielding

src/cli.zig

@@ -95,22 +95,16 @@ pub fn run() !void {
     try git.init();
     defer git.deinit();
 
-    // Native commands — optimized output via libgit2
+    var repo = try openRepo();
+    defer repo.deinit();
+
     if (std.mem.eql(u8, cmd, "status") or std.mem.eql(u8, cmd, "s")) {
-        var repo = try openRepo(w);
-        defer repo.deinit();
         try status.run(repo.repo, human, w);
     } else if (std.mem.eql(u8, cmd, "log") or std.mem.eql(u8, cmd, "l")) {
-        var repo = try openRepo(w);
-        defer repo.deinit();
         try log.run(repo.repo, human, count, w);
     } else if (std.mem.eql(u8, cmd, "diff") or std.mem.eql(u8, cmd, "d")) {
-        var repo = try openRepo(w);
-        defer repo.deinit();
         try diff.run(repo.repo, human, staged, w);
     } else if (std.mem.eql(u8, cmd, "show")) {
-        var repo = try openRepo(w);
-        defer repo.deinit();
         // Find revision arg (first non-flag arg after "show")
         var rev: ?[]const u8 = null;
         for (args[2..]) |arg| {
@@ -125,7 +119,7 @@ pub fn run() !void {
     try w.flush();
 }
 
-fn openRepo(_: *std.Io.Writer) !git.Repository {
+fn openRepo() !git.Repository {
     return git.Repository.openFromCwd() catch {
         std.debug.print("fatal: not a git repository\n", .{});
         std.process.exit(128);

src/cmd/diff.zig

@@ -2,6 +2,7 @@ const std = @import("std");
 const git = @import("../git.zig");
 const c = git.c;
 const color = @import("../color.zig");
+const fmt = @import("../fmt.zig");
 
 const Writer = std.Io.Writer;
 
@@ -15,6 +16,7 @@ pub fn run(repo: *c.git_repository, human: bool, staged: bool, w: *Writer) !void
     var diff_result: ?*c.git_diff = null;
 
     if (staged) {
+        // Diff HEAD to index. HEAD may not exist yet (initial commit).
         var head: ?*c.git_object = null;
         _ = c.git_revparse_single(&head, repo, "HEAD");
         defer if (head != null) c.git_object_free(head);
@@ -41,194 +43,19 @@ pub fn run(repo: *c.git_repository, human: bool, staged: bool, w: *Writer) !void
     if (human) {
         try printHuman(diff_result, w);
     } else {
-        var ctx = PrintCtx{ .writer = w, .last_file = null };
-        _ = c.git_diff_print(diff_result, c.GIT_DIFF_FORMAT_PATCH, compactCallback, @ptrCast(&ctx));
+        var ctx = fmt.CompactCtx{ .writer = w };
+        _ = c.git_diff_print(diff_result, c.GIT_DIFF_FORMAT_PATCH, fmt.compactCallback, @ptrCast(&ctx));
     }
 }
 
-// --- Compact (agent) output ---
-
-const PrintCtx = struct {
-    writer: *Writer,
-    last_file: ?[*:0]const u8,
-};
-
-fn compactCallback(
-    delta: [*c]const c.git_diff_delta,
-    _: [*c]const c.git_diff_hunk,
-    line: [*c]const c.git_diff_line,
-    payload: ?*anyopaque,
-) callconv(.c) c_int {
-    const ctx: *PrintCtx = @ptrCast(@alignCast(payload));
-    const content = line.*.content;
-    const len = line.*.content_len;
-
-    if (len == 0 or content == null) return 0;
-
-    const slice = content[0..len];
-    const w = ctx.writer;
-
-    switch (line.*.origin) {
-        '+', '-', ' ' => {
-            w.writeByte(@intCast(line.*.origin)) catch return -1;
-            w.writeAll(slice) catch return -1;
-        },
-        'H' => {
-            // Strip trailing context text after closing @@
-            if (std.mem.indexOf(u8, slice, " @@")) |pos| {
-                w.writeAll(slice[0 .. pos + 3]) catch return -1;
-                w.writeByte('\n') catch return -1;
-            } else {
-                w.writeAll(slice) catch return -1;
-            }
-        },
-        'F' => {
-            if (delta != null) {
-                const path = delta.*.new_file.path;
-                if (path != null) {
-                    if (slice.len >= 4 and std.mem.eql(u8, slice[0..4], "diff")) {
-                        w.writeAll("--- ") catch return -1;
-                        w.writeAll(std.mem.span(path)) catch return -1;
-                        w.writeByte('\n') catch return -1;
-                    }
-                }
-            }
-        },
-        else => {},
-    }
-
-    return 0;
-}
-
-// --- Human output ---
-
 fn printHuman(diff_result: ?*c.git_diff, w: *Writer) !void {
     const use_color = color.isTty();
-
-    // Print per-file stat + patch
     const num_deltas = c.git_diff_num_deltas(diff_result);
     if (num_deltas == 0) return;
 
-    // Collect stats first
-    var stats: ?*c.git_diff_stats = null;
-    try git.check(c.git_diff_get_stats(&stats, diff_result));
-    defer c.git_diff_stats_free(stats);
-
-    const total_files = c.git_diff_stats_files_changed(stats);
-    const total_add = c.git_diff_stats_insertions(stats);
-    const total_del = c.git_diff_stats_deletions(stats);
-
-    // Summary line
-    if (use_color) {
-        try w.print("{s}{d} file{s}{s}, ", .{ color.bold, total_files, if (total_files != 1) "s" else "", color.reset });
-        try w.print("{s}+{d}{s} ", .{ color.bright_green, total_add, color.reset });
-        try w.print("{s}-{d}{s}\n\n", .{ color.bright_red, total_del, color.reset });
-    } else {
-        try w.print("{d} file{s}, +{d} -{d}\n\n", .{ total_files, if (total_files != 1) "s" else "", total_add, total_del });
-    }
-
-    // Print each file's patch
-    var ctx = HumanCtx{ .writer = w, .use_color = use_color, .current_file = null };
-    _ = c.git_diff_print(diff_result, c.GIT_DIFF_FORMAT_PATCH, humanCallback, @ptrCast(&ctx));
-}
-
-const HumanCtx = struct {
-    writer: *Writer,
-    use_color: bool,
-    current_file: ?[*:0]const u8,
-};
-
-fn humanCallback(
-    delta: [*c]const c.git_diff_delta,
-    _: [*c]const c.git_diff_hunk,
-    line: [*c]const c.git_diff_line,
-    payload: ?*anyopaque,
-) callconv(.c) c_int {
-    const ctx: *HumanCtx = @ptrCast(@alignCast(payload));
-    const content = line.*.content;
-    const len = line.*.content_len;
-
-    if (len == 0 or content == null) return 0;
-
-    const slice = content[0..len];
-    const w = ctx.writer;
-
-    switch (line.*.origin) {
-        'F' => {
-            // File header - print a clean colored separator on first line only
-            if (delta != null) {
-                const path = delta.*.new_file.path;
-                if (path != null and slice.len >= 4 and std.mem.eql(u8, slice[0..4], "diff")) {
-                    // Check if this is a new file vs the last one we printed
-                    const new_path = path;
-                    if (ctx.current_file == null or ctx.current_file != new_path) {
-                        if (ctx.current_file != null) {
-                            // Separator between files
-                            w.writeByte('\n') catch return -1;
-                        }
-                        ctx.current_file = new_path;
-
-                        const path_str = std.mem.span(path);
-
-                        if (ctx.use_color) {
-                            // Bold filename
-                            w.writeAll(color.bold) catch return -1;
-                            w.writeAll(path_str) catch return -1;
-                            w.writeAll(color.reset) catch return -1;
-                            w.writeByte('\n') catch return -1;
-                        } else {
-                            w.writeAll(path_str) catch return -1;
-                            w.writeByte('\n') catch return -1;
-                        }
-                    }
-                }
-            }
-        },
-        'H' => {
-            // Hunk header
-            if (ctx.use_color) {
-                w.writeAll(color.cyan) catch return -1;
-                w.writeAll(slice) catch return -1;
-                w.writeAll(color.reset) catch return -1;
-            } else {
-                w.writeAll(slice) catch return -1;
-            }
-        },
-        '+' => {
-            if (ctx.use_color) {
-                w.writeAll(color.bright_green) catch return -1;
-                w.writeByte('+') catch return -1;
-                w.writeAll(slice) catch return -1;
-                w.writeAll(color.reset) catch return -1;
-            } else {
-                w.writeByte('+') catch return -1;
-                w.writeAll(slice) catch return -1;
-            }
-        },
-        '-' => {
-            if (ctx.use_color) {
-                w.writeAll(color.bright_red) catch return -1;
-                w.writeByte('-') catch return -1;
-                w.writeAll(slice) catch return -1;
-                w.writeAll(color.reset) catch return -1;
-            } else {
-                w.writeByte('-') catch return -1;
-                w.writeAll(slice) catch return -1;
-            }
-        },
-        ' ' => {
-            if (ctx.use_color) {
-                w.writeAll(color.dim) catch return -1;
-                w.writeByte(' ') catch return -1;
-                w.writeAll(slice) catch return -1;
-                w.writeAll(color.reset) catch return -1;
-            } else {
-                w.writeByte(' ') catch return -1;
-                w.writeAll(slice) catch return -1;
-            }
-        },
-        else => {},
-    }
+    try fmt.writeStat(diff_result, use_color, w);
+    try w.writeByte('\n');
 
-    return 0;
+    var ctx = fmt.HumanCtx{ .writer = w, .use_color = use_color, .current_file = null };
+    _ = c.git_diff_print(diff_result, c.GIT_DIFF_FORMAT_PATCH, fmt.humanCallback, @ptrCast(&ctx));
 }

src/cmd/log.zig

@@ -1,10 +1,10 @@
 const std = @import("std");
 const git = @import("../git.zig");
 const c = git.c;
-const clr = @import("../color.zig");
+const color = @import("../color.zig");
+const fmt = @import("../fmt.zig");
 
 const Writer = std.Io.Writer;
-const default_count: usize = 20;
 
 pub fn run(repo: *c.git_repository, human: bool, count: usize, w: *Writer) !void {
     var walk: ?*c.git_revwalk = null;
@@ -16,9 +16,8 @@ pub fn run(repo: *c.git_repository, human: bool, count: usize, w: *Writer) !void
 
     var oid: c.git_oid = undefined;
     var shown: usize = 0;
-    const max = if (count == 0) default_count else count;
 
-    while (shown < max) {
+    while (shown < count) {
         const err = c.git_revwalk_next(&oid, walk);
         if (err < 0) break;
 
@@ -33,33 +32,16 @@ pub fn run(repo: *c.git_repository, human: bool, count: usize, w: *Writer) !void
         const short_hash = oid_buf[0..7];
 
         if (human) {
-            const use_color = clr.isTty();
-            const time = c.git_commit_time(commit);
-            const ts: u64 = @intCast(time);
-            const epoch = std.time.epoch.EpochSeconds{ .secs = ts };
-            const day = epoch.getEpochDay();
-            const yd = day.calculateYearDay();
-            const md = yd.calculateMonthDay();
+            const use_color = color.isTty();
+            const d = fmt.epochToDate(c.git_commit_time(commit));
             if (use_color) {
                 try w.print("{s}{s}{s} {s}{d}-{d:0>2}-{d:0>2}{s} {s}\n", .{
-                    clr.yellow,
-                    short_hash,
-                    clr.reset,
-                    clr.dim,
-                    yd.year,
-                    @intFromEnum(md.month),
-                    md.day_index + 1,
-                    clr.reset,
+                    color.yellow, short_hash, color.reset,
+                    color.dim,    d.year,     d.month, d.day, color.reset,
                     summary,
                 });
             } else {
-                try w.print("{s} {d}-{d:0>2}-{d:0>2} {s}\n", .{
-                    short_hash,
-                    yd.year,
-                    @intFromEnum(md.month),
-                    md.day_index + 1,
-                    summary,
-                });
+                try w.print("{s} {d}-{d:0>2}-{d:0>2} {s}\n", .{ short_hash, d.year, d.month, d.day, summary });
             }
         } else {
             try w.print("{s} {s}\n", .{ short_hash, summary });