feat(builtins): implement jq setpath, leaf_paths, fix match/scan

Prepend custom jq definitions to every filter to patch jaq limitations:

- setpath(p; v): recursive path-setting, not in jaq stdlib
- leaf_paths: paths to scalar leaves via paths(scalars)
- match: adds "name":null to unnamed captures (jaq omitted it)
- scan: uses "g" flag for global matching (jq default behavior)

The // alternative operator on null remains skipped (jaq core limitation).

Enable 4 previously-skipped spec tests. Skip count: 18 -> 14.

Closes #328

https://claude.ai/code/session_01QbjrsMFJbHy5XfHCzA6TjM

Author: claude

crates/bashkit/src/builtins/jq.rs

@@ -22,6 +22,32 @@ use crate::interpreter::ExecResult;
 /// produce deeply nested parse trees in jaq.
 const MAX_JQ_JSON_DEPTH: usize = 100;
 
+/// Custom jq definitions prepended to every filter to patch jaq limitations:
+/// - `setpath(p; v)`: recursive path-setting (not in jaq stdlib)
+/// - `leaf_paths`: paths to scalar leaves (not in jaq stdlib)
+/// - `match` override: adds `"name":null` to unnamed captures
+/// - `scan` override: uses "g" flag for global matching (jq default)
+const JQ_COMPAT_DEFS: &str = r#"
+def setpath(p; v):
+  if (p | length) == 0 then v
+  else p[0] as $k |
+    (if . == null then
+      if ($k | type) == "number" then [] else {} end
+    else . end) |
+    .[$k] |= setpath(p[1:]; v)
+  end;
+def leaf_paths: paths(scalars);
+def match(re; flags):
+  matches(re; flags)[] |
+  .[0] as $m |
+  { offset: $m.offset, length: $m.length, string: $m.string,
+    captures: [.[1:][] | { offset: .offset, length: .length, string: .string,
+    name: (if has("name") then .name else null end) }] };
+def match(re): match(re; "");
+def scan(re; flags): matches(re; "g" + flags)[] | .[0].string;
+def scan(re): scan(re; "");
+"#;
+
 /// RAII guard that restores process env vars when dropped.
 /// Ensures cleanup even on early-return error paths.
 struct EnvRestoreGuard(Vec<(String, Option<String>)>);
@@ -297,6 +323,11 @@ impl Builtin for Jq {
         let loader = load::Loader::new(jaq_std::defs().chain(jaq_json::defs()));
         let arena = load::Arena::default();
 
+        // Prepend compatibility definitions (setpath, leaf_paths, match, scan)
+        // to override jaq's defaults with jq-compatible behavior.
+        let compat_filter = format!("{}{}", JQ_COMPAT_DEFS, filter);
+        let filter = compat_filter.as_str();
+
         // Parse the filter
         let program = load::File {
             code: filter,

crates/bashkit/tests/spec_cases/jq/jq.test.sh

@@ -512,10 +512,13 @@ echo '{"a":{"b":1}}' | jq 'getpath(["a","b"])'
 ### end
 
 ### jq_setpath
-### skip: setpath not available in jaq standard library
+# Set value at path
 echo '{"a":1}' | jq 'setpath(["b"];2)'
 ### expect
-{"a":1,"b":2}
+{
+  "a": 1,
+  "b": 2
+}
 ### end
 
 ### jq_del
@@ -577,10 +580,15 @@ echo '{"a":{"b":1}}' | jq '[paths]'
 ### end
 
 ### jq_leaf_paths
-### skip: leaf_paths not available in jaq standard library
+# Get paths to leaf (scalar) values
 echo '{"a":{"b":1}}' | jq '[leaf_paths]'
 ### expect
-[["a","b"]]
+[
+  [
+    "a",
+    "b"
+  ]
+]
 ### end
 
 ### jq_any
@@ -758,15 +766,15 @@ true
 ### end
 
 ### jq_match
-### skip: jaq omits capture name field (real jq includes "name":null)
-echo '"hello"' | jq 'match("e(ll)o")'
+### bash_diff: jaq/serde_json sorts object keys alphabetically vs jq insertion order
+echo '"hello"' | jq -c 'match("e(ll)o")'
 ### expect
-{"offset":1,"length":4,"string":"ello","captures":[{"offset":2,"length":2,"string":"ll","name":null}]}
+{"captures":[{"length":2,"name":null,"offset":2,"string":"ll"}],"length":4,"offset":1,"string":"ello"}
 ### end
 
 ### jq_scan
-### skip: jaq scan requires explicit "g" flag for global match
-echo '"hello hello"' | jq '[scan("hel")]'
+# Scan for all regex matches
+echo '"hello hello"' | jq -c '[scan("hel")]'
 ### expect
 ["hel","hel"]
 ### end

crates/bashkit/tests/spec_tests.rs

@@ -8,7 +8,7 @@
 //! - `### skip: reason` - Skip test entirely (not run in any test)
 //! - `### bash_diff: reason` - Known difference from real bash (runs in spec tests, excluded from comparison)
 //!
-//! ## Skipped Tests (18 total)
+//! ## Skipped Tests (14 total)
 //!
 //! Actual `### skip:` markers across spec test files:
 //!
@@ -21,12 +21,8 @@
 //! - [ ] od output format varies
 //! - [ ] hexdump -C output format varies
 //!
-//! ### jq.test.sh (5 skipped)
+//! ### jq.test.sh (1 skipped)
 //! - [ ] jaq errors on .foo applied to null instead of returning null for //
-//! - [ ] setpath not available in jaq standard library
-//! - [ ] leaf_paths not available in jaq standard library
-//! - [ ] jaq omits capture name field (real jq includes "name":null)
-//! - [ ] jaq scan requires explicit "g" flag for global match
 //!
 //! ### python.test.sh (8 skipped)
 //! - [ ] Monty does not support set & and | operators yet