Fix commit-diff timeout regression test

TESTING_GUIDE.md

@@ -19,6 +19,7 @@ Use the full suite by default. Use targeted filters only while iterating locally
 
 ## Test Stack
 
+- Issue #5130 keeps the commit-diff timeout regression focused on `diff-tree`: its fake git must echo the commit being verified by `rev-parse --verify <ref>^{commit}`, then the test must confirm the timed-out child process is reaped. Keep production single-commit validation strict.
 - Issue #5128 compact graph zero-result coverage belongs in `JsonEnvelopeWrapperIssue4585Tests.cs`. Keep `callees` aligned with `references` and `callers` by asserting an empty compact location envelope and zero returned/total cardinality both with and without explicit `--fields`, while reusing the graph-ready bounded-response fixture.
 - Issue #5098 inspect projection coverage belongs in `QueryCommandRunnerInspectTests.cs`. Keep one graph-ready partial-type fixture covering canonical and alias selectors, multiple leaves across collections, parent-over-child precedence, stable row order, empty arrays, compact truncation, byte bounds, body paging/recovery, partial-family metadata, queryless catalog discovery, and typed unknown parent/leaf errors. `ConsoleUiTests.cs` separately pins the `<csv|list>` usage, nested-field help text, and examples.
 - Path-containment coverage for #5091 pairs platform-independent `PathCasingTests` seams for mixed parent-namespace case policies and directory identities with `FileIndexerTests` integration through an internal file symlink. Keep both checks when changing internal-symlink policy: a case-insensitive project mount must not make a distinct case-only sibling in its case-sensitive parent namespace appear internal, while genuine same-namespace aliases remain accepted.
@@ -1114,6 +1115,7 @@ dotnet test --filter "FullyQualifiedName~GitHelperTests"
 
 ## テストスタック
 
+- Issue #5130 の commit-diff timeout regression は `diff-tree` に焦点を維持します。fake git は `rev-parse --verify <ref>^{commit}` で検証対象の commit を返し、テストでは timeout した子プロセスが reap されることを確認してください。本番の single-commit validation は厳格なままにします。
 - Issue #5128 の compact graph 0件 coverage は `JsonEnvelopeWrapperIssue4585Tests.cs` が担当します。graph-ready な bounded-response fixture を再利用し、明示的な `--fields` の有無の両方で、`callees` が `references` / `callers` と同様に空の compact location envelope と返却件数・総件数0を維持することを検証してください。
 - Issue #5098 の inspect projection coverage は `QueryCommandRunnerInspectTests.cs` が担当します。graph-ready な partial type fixture 1つで canonical / alias selector、collection をまたぐ複数 leaf、parent の child に対する優先、安定した row 順、空配列、compact truncation、byte 上限、body paging / recovery、partial-family metadata、query 不要の catalog discovery、未知 parent / leaf の型付き error を維持してください。`ConsoleUiTests.cs` では `<csv|list>` usage、nested-field help text、例を別途固定します。
 - #5091 の path containment coverage は、親 directory namespace の case policy と directory identity が混在する状況を OS 非依存で再現する `PathCasingTests` の seam と、内部 file symlink を通す `FileIndexerTests` の integration を対にします。internal-symlink policy を変更するときは両方を維持し、case-insensitive な project mount の policy で、case-sensitive な親 namespace にある別 identity の case-only sibling を内部 path と誤認しないこと、および同一 namespace の正当な alias は引き続き受理されることを検証してください。

changelog.d/unreleased/5130.fixed.md

@@ -0,0 +1,16 @@
+---
+category: fixed
+issues:
+  - 5130
+affected:
+  - tests/CodeIndex.Tests/GitHelperTests.cs
+  - TESTING_GUIDE.md
+---
+
+## English
+
+- **The commit-diff timeout regression now reaches `diff-tree` (#5130)** — the fake git validation response follows the temporary commit under test, preserving strict single-commit validation while allowing the timeout path to verify child-process cleanup.
+
+## 日本語
+
+- **commit-diff timeout regression が `diff-tree` に到達するようになりました (#5130)** — fake git の validation 応答をテスト対象の一時 commit と一致させ、厳格な single-commit validation を維持しながら timeout 経路で子プロセスの cleanup を検証できるようにしました。

tests/CodeIndex.Tests/GitHelperTests.cs

@@ -732,7 +732,7 @@ public void GetChangedFilesFromCommit_FailsWhenGitCommandTimesOut()
 
         var fakeGitDir = Path.Combine(_tempDir, "fake-git-timeout");
         Directory.CreateDirectory(fakeGitDir);
-        WriteFakeGitThatHangsOnDiffTree(fakeGitDir);
+        WriteFakeGitThatHangsOnDiffTree(fakeGitDir, commitId);
         var fakeGitPidPath = Path.Combine(fakeGitDir, "diff-tree.pid");
 
         var oldGitExecutablePath = GitHelper.GitExecutablePathOverride;
@@ -971,7 +971,8 @@ public void GetChangedFilesFromCommit_CancelDuringGitCommand_ThrowsOperationCanc
         Directory.CreateDirectory(repoDir);
         var fakeGitDir = Path.Combine(_tempDir, "fake-git-cancel");
         Directory.CreateDirectory(fakeGitDir);
-        WriteFakeGitThatHangsOnDiffTree(fakeGitDir);
+        const string commitId = "0123456789abcdef";
+        WriteFakeGitThatHangsOnDiffTree(fakeGitDir, commitId);
 
         var oldGitExecutablePath = GitHelper.GitExecutablePathOverride;
         GitHelper.GitExecutablePathOverride = Path.Combine(fakeGitDir, "git");
@@ -982,7 +983,7 @@ public void GetChangedFilesFromCommit_CancelDuringGitCommand_ThrowsOperationCanc
             var stopwatch = Stopwatch.StartNew();
 
             var ex = Assert.Throws<OperationCanceledException>(
-                () => GitHelper.GetChangedFilesFromCommit(repoDir, "0123456789abcdef", cts.Token));
+                () => GitHelper.GetChangedFilesFromCommit(repoDir, commitId, cts.Token));
 
             stopwatch.Stop();
             Assert.Equal(cts.Token, ex.CancellationToken);
@@ -1835,27 +1836,29 @@ exit 0
             File.SetUnixFileMode(script, UnixFileMode.UserRead | UnixFileMode.UserWrite | UnixFileMode.UserExecute);
     }
 
-    private static void WriteFakeGitThatHangsOnDiffTree(string directory)
+    private static void WriteFakeGitThatHangsOnDiffTree(string directory, string verifiedCommit)
     {
         var script = Path.Combine(directory, "git");
-        File.WriteAllText(script, $$"""
+        File.WriteAllText(script, """
 #!/bin/sh
 if [ "$1" = "rev-parse" ]; then
   if [ "$2" = "--symbolic-full-name" ]; then
     exit 0
   fi
   if [ "$2" = "--verify" ]; then
-    printf '%s\n' '0123456789abcdef0123456789abcdef01234567'
+    printf '%s\n' '__VERIFIED_COMMIT__'
     exit 0
   fi
 fi
 if [ "$1" = "diff-tree" ]; then
   printf '%s\n' "$$" > "$(dirname "$0")/diff-tree.pid"
-  sleep {{FakeGitHangSeconds}}
+  sleep __HANG_SECONDS__
   exit 0
 fi
 exit 1
-""");
+"""
+            .Replace("__VERIFIED_COMMIT__", verifiedCommit, StringComparison.Ordinal)
+            .Replace("__HANG_SECONDS__", FakeGitHangSeconds.ToString(System.Globalization.CultureInfo.InvariantCulture), StringComparison.Ordinal));
         if (!OperatingSystem.IsWindows())
             File.SetUnixFileMode(script, UnixFileMode.UserRead | UnixFileMode.UserWrite | UnixFileMode.UserExecute);
     }