perf(#311): index subrepo routing by first path segment (#390)

cmdCommitToSubrepo routed each changed file to a sub-repo via
subRepos.find(...) inside the file loop — O(files * repos). Extract a pure
groupFilesBySubrepo() that buckets sub-repos by first path segment and scans
only the matching bucket, dropping it to expected O(files + repos). First-
match-in-array-order semantics (incl. multi-segment sub-repos) are preserved
exactly. Adds the first behavior-lock test for the routing path.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.changeset/311-subrepo-routing-index.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 311
+---
+Route changed files to sub-repos via a first-segment bucket index instead of an O(files*repos) linear scan (#311).

get-shit-done/bin/lib/commands.cjs

@@ -366,6 +366,43 @@ function cmdCommit(cwd, message, files, raw, amend, noVerify) {
   output(result, raw, hash || 'committed');
 }
 
+/**
+ * Route a list of changed files to their sub-repo prefixes.
+ *
+ * Bucket sub-repos by their first path segment. Any file that matches a
+ * sub-repo prefix must share that sub-repo's first segment, so we only scan
+ * the (small) bucket for the file's first segment instead of all sub-repos
+ * — O(F + R) expected vs the prior O(F*R) find-in-loop. Candidates stay in
+ * sub-repo array order, preserving the original first-match semantics
+ * (incl. multi-segment sub-repos like "vendor/pkg", which resolve via the
+ * inner startsWith). (#311)
+ *
+ * @param {string[]} files    - changed file paths (relative to project root)
+ * @param {string[]} subRepos - sub-repo path prefixes from config.sub_repos
+ * @returns {{ grouped: Object<string,string[]>, unmatched: string[] }}
+ */
+function groupFilesBySubrepo(files, subRepos) {
+  const reposByFirstSeg = new Map();
+  for (const repo of subRepos) {
+    const firstSeg = String(repo).split('/')[0];
+    let bucket = reposByFirstSeg.get(firstSeg);
+    if (!bucket) { bucket = []; reposByFirstSeg.set(firstSeg, bucket); }
+    bucket.push(repo);
+  }
+  const grouped = {};
+  const unmatched = [];
+  for (const file of files) {
+    const candidates = reposByFirstSeg.get(file.split('/')[0]);
+    const match = candidates ? candidates.find(repo => file.startsWith(repo + '/')) : undefined;
+    if (match) {
+      (grouped[match] ||= []).push(file);
+    } else {
+      unmatched.push(file);
+    }
+  }
+  return { grouped, unmatched };
+}
+
 function cmdCommitToSubrepo(cwd, message, files, raw) {
   if (!message) {
     error('commit message required');
@@ -383,17 +420,7 @@ function cmdCommitToSubrepo(cwd, message, files, raw) {
   }
 
   // Group files by sub-repo prefix
-  const grouped = {};
-  const unmatched = [];
-  for (const file of files) {
-    const match = subRepos.find(repo => file.startsWith(repo + '/'));
-    if (match) {
-      if (!grouped[match]) grouped[match] = [];
-      grouped[match].push(file);
-    } else {
-      unmatched.push(file);
-    }
-  }
+  const { grouped, unmatched } = groupFilesBySubrepo(files, subRepos);
 
   if (unmatched.length > 0) {
     process.stderr.write(`Warning: ${unmatched.length} file(s) did not match any sub-repo prefix: ${unmatched.join(', ')}\n`);
@@ -1015,6 +1042,7 @@ function cmdCheckCommit(cwd, raw) {
 }
 
 module.exports = {
+  groupFilesBySubrepo,
   determinePhaseStatus,
   cmdGenerateSlug,
   cmdCurrentTimestamp,

tests/commands.test.cjs

@@ -1388,6 +1388,76 @@ describe('commit command', () => {
   });
 });
 
+// ─────────────────────────────────────────────────────────────────────────────
+// groupFilesBySubrepo tests (#311)
+// ─────────────────────────────────────────────────────────────────────────────
+
+describe('groupFilesBySubrepo (#311)', () => {
+  const { groupFilesBySubrepo } = require('../get-shit-done/bin/lib/commands.cjs');
+
+  test('single-segment subrepos route files correctly and unmatched collected', () => {
+    const result = groupFilesBySubrepo(
+      ['packages/a.js', 'docs/x.md', 'README.md'],
+      ['packages', 'docs']
+    );
+    assert.deepStrictEqual(result.grouped, { packages: ['packages/a.js'], docs: ['docs/x.md'] });
+    assert.deepStrictEqual(result.unmatched, ['README.md']);
+  });
+
+  test('multi-segment subrepo matches deep files, not shallow sibling', () => {
+    const result = groupFilesBySubrepo(
+      ['vendor/pkg/x.js', 'vendor/other.js', 'vendor/pkg/y.js'],
+      ['vendor/pkg']
+    );
+    assert.deepStrictEqual(result.grouped, { 'vendor/pkg': ['vendor/pkg/x.js', 'vendor/pkg/y.js'] });
+    assert.deepStrictEqual(result.unmatched, ['vendor/other.js']);
+  });
+
+  test('first-match-in-array-order wins (not longest-prefix)', () => {
+    // 'app' comes before 'app/sub' in subRepos array; 'app/sub/f.js' matches 'app' first
+    const result = groupFilesBySubrepo(
+      ['app/sub/f.js'],
+      ['app', 'app/sub']
+    );
+    assert.deepStrictEqual(result.grouped, { app: ['app/sub/f.js'] });
+    assert.deepStrictEqual(result.unmatched, []);
+  });
+
+  test('file with no slash does not match a same-name subrepo', () => {
+    const result = groupFilesBySubrepo(['top'], ['top']);
+    assert.deepStrictEqual(result.grouped, {});
+    assert.deepStrictEqual(result.unmatched, ['top']);
+  });
+
+  test('file with slash after prefix routes correctly', () => {
+    const result = groupFilesBySubrepo(['top/a'], ['top']);
+    assert.deepStrictEqual(result.grouped, { top: ['top/a'] });
+    assert.deepStrictEqual(result.unmatched, []);
+  });
+
+  test('empty files list returns empty grouped and unmatched', () => {
+    const result = groupFilesBySubrepo([], ['a']);
+    assert.deepStrictEqual(result.grouped, {});
+    assert.deepStrictEqual(result.unmatched, []);
+  });
+
+  test('empty subRepos list puts all files in unmatched', () => {
+    const result = groupFilesBySubrepo(['a/b'], []);
+    assert.deepStrictEqual(result.grouped, {});
+    assert.deepStrictEqual(result.unmatched, ['a/b']);
+  });
+
+  test('non-string subRepos entry does not throw and string entries still route (#311)', () => {
+    // Old inline code coerced non-string repos via `repo + '/'` and never threw.
+    let result;
+    assert.doesNotThrow(() => {
+      result = groupFilesBySubrepo(['a/b', 'README.md'], [null, 'a']);
+    });
+    assert.deepStrictEqual(result.grouped, { a: ['a/b'] });
+    assert.deepStrictEqual(result.unmatched, ['README.md']);
+  });
+});
+
 // ─────────────────────────────────────────────────────────────────────────────
 // cmdWebsearch tests (CMD-05)
 // ─────────────────────────────────────────────────────────────────────────────