fix(web): use blame line's path when navigating to commit diff

When a file has been renamed, blame lines may be attributed to commits
where the file existed at a different path. Previously, clicking a
commit in the blame gutter navigated using the current file path, which
could resolve to a file that didn't exist at that commit.

Capture the per-commit `filename` field from `git blame --porcelain`
(emitted only on the first global appearance of each commit) and attach
it as `path` to each blame range. Plumb it through `LineEntry` so the
commit-click handler navigates to the correct historical path.

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

Author: brendan-kellam

packages/web/src/app/(app)/browse/[...path]/components/codePreviewPanel/blameGutterExtension.ts

@@ -7,6 +7,10 @@ import { BLAME_AGE_BG_CLASSES, computeAgeBucket } from "./blameAgeColors";
 
 type LineEntry = {
     hash: string;
+    // The file path as it existed at `hash`. May differ from the current file
+    // path if the file was renamed in or after that commit, so we use it
+    // (rather than the current path) when navigating to the commit's diff.
+    path: string;
     // Set only on the first line of a contiguous range; null on continuation
     // lines so they render as empty filler cells.
     message: string | null;
@@ -29,7 +33,7 @@ const FILE_STACK_SVG = '<svg xmlns="http://www.w3.org/2000/svg" width="14" heigh
 
 const buildCellDom = (
     entry: LineEntry,
-    onCommitClick: (hash: string) => void,
+    onCommitClick: (commit: { hash: string; path: string }) => void,
     onReblameClick: (previous: { hash: string; path: string }) => void,
 ): HTMLElement => {
     const cell = document.createElement('div');
@@ -80,7 +84,7 @@ const buildCellDom = (
     messageEl.type = 'button';
     messageEl.className = 'flex-1 min-w-0 truncate text-left bg-transparent border-0 p-0 m-0 font-[inherit] text-inherit cursor-pointer hover:text-foreground hover:underline';
     messageEl.textContent = entry.message;
-    messageEl.addEventListener('click', () => onCommitClick(entry.hash));
+    messageEl.addEventListener('click', () => onCommitClick({ hash: entry.hash, path: entry.path }));
     cell.appendChild(messageEl);
 
     if (entry.previous) {
@@ -103,7 +107,7 @@ const buildCellDom = (
 class BlameMarker extends GutterMarker {
     constructor(
         readonly entry: LineEntry,
-        readonly onCommitClick: (hash: string) => void,
+        readonly onCommitClick: (commit: { hash: string; path: string }) => void,
         readonly onReblameClick: (previous: { hash: string; path: string }) => void,
     ) {
         super();
@@ -117,6 +121,7 @@ class BlameMarker extends GutterMarker {
         const b = other.entry;
         return (
             a.hash === b.hash &&
+            a.path === b.path &&
             a.message === b.message &&
             a.date === b.date &&
             a.authorEmail === b.authorEmail &&
@@ -199,6 +204,7 @@ const buildLineIndex = (blame: FileBlameResponse): Map<number, LineEntry> => {
             if (isFirstLineOfRange && commit) {
                 index.set(lineNumber, {
                     hash: range.hash,
+                    path: range.path,
                     message: commit.message,
                     date: commit.date,
                     authorEmail: commit.authorEmail,
@@ -209,6 +215,7 @@ const buildLineIndex = (blame: FileBlameResponse): Map<number, LineEntry> => {
             } else {
                 index.set(lineNumber, {
                     hash: range.hash,
+                    path: range.path,
                     message: null,
                     date: null,
                     authorEmail: null,
@@ -236,7 +243,7 @@ const blameTheme = EditorView.theme({
 
 export const blameGutterExtension = (
     blame: FileBlameResponse,
-    onCommitClick: (hash: string) => void,
+    onCommitClick: (commit: { hash: string; path: string }) => void,
     onReblameClick: (previous: { hash: string; path: string }) => void,
 ): Extension => {
     const lineIndex = buildLineIndex(blame);

packages/web/src/app/(app)/browse/[...path]/components/codePreviewPanel/pureCodePreviewPanel.tsx

@@ -42,16 +42,16 @@ export const PureCodePreviewPanel = ({
     const hasCodeNavEntitlement = useHasEntitlement("code-nav");
     const router = useRouter();
 
-    const handleBlameCommitClick = useCallback((hash: string) => {
+    const handleBlameCommitClick = useCallback((commit: { hash: string; path: string }) => {
         router.push(getBrowsePath({
             repoName,
             revisionName,
-            path,
+            path: commit.path,
             pathType: 'blob',
-            previewRef: hash,
+            previewRef: commit.hash,
             diff: true,
         }));
-    }, [router, repoName, revisionName, path]);
+    }, [router, repoName, revisionName]);
 
     const handleBlameReblameClick = useCallback((previous: { hash: string; path: string }) => {
         router.push(getBrowsePath({

packages/web/src/features/git/getFileBlameApi.ts

@@ -21,23 +21,27 @@ type CommitMeta = FileBlameResponse['commits'][string];
  * Format reference: each blamed line produces an entry of the form
  *
  *   <hash> <orig-line> <final-line> [<num-lines>]  (4-field header → first line of a group)
- *   [author <name>                                 (metadata block, only on first
- *    author-mail <<email>>                          appearance of a commit globally)
- *    author-time <unix-ts>
- *    author-tz <+/-HHMM>
- *    committer ...
- *    summary <subject>
+ *   [author <name>                                 (metadata block, emitted only on
+ *    author-mail <<email>>                          the first global appearance of a
+ *    author-time <unix-ts>                          commit; subsequent groups for the
+ *    author-tz <+/-HHMM>                            same commit are header-only. With
+ *    committer ...                                  -C/-M, `filename` may be re-emitted
+ *    summary <subject>                              if it differs from the prior value.)
  *    previous <hash> <path>                         (optional)
  *    filename <path>]
  *   \t<line content>
  *
  * Within a contiguous group of lines from the same commit, only the first line's
  * header carries `<num-lines>`; subsequent lines have a 3-field header. We detect
  * group boundaries via the presence of `<num-lines>` and emit one range per group.
+ *
+ * Because `filename` is emitted per-commit (not per-group), we cache it in
+ * `filenameByHash` and look it up when pushing a range.
  */
 const parsePorcelainBlame = (output: string): FileBlameResponse => {
     const ranges: FileBlameResponse['ranges'] = [];
     const commits: Record<string, CommitMeta> = {};
+    const filenameByHash = new Map<string, string>();
 
     if (output.length === 0) {
         return { ranges, commits };
@@ -102,8 +106,10 @@ const parsePorcelainBlame = (output: string): FileBlameResponse => {
                         path: value.substring(sep + 1),
                     };
                 }
+            } else if (key === 'filename') {
+                filenameByHash.set(hash, value);
             }
-            // committer*, filename, boundary are intentionally ignored.
+            // committer*, boundary are intentionally ignored.
 
             i++;
         }
@@ -125,7 +131,11 @@ const parsePorcelainBlame = (output: string): FileBlameResponse => {
         }
 
         if (isGroupStart) {
-            ranges.push({ hash, startLine: finalLine, lineCount });
+            const path = filenameByHash.get(hash);
+            if (path === undefined) {
+                throw new Error(`Malformed git blame porcelain output: missing "filename" for commit ${hash}`);
+            }
+            ranges.push({ hash, path, startLine: finalLine, lineCount });
         }
     }
 
@@ -136,7 +146,7 @@ const parsePorcelainBlame = (output: string): FileBlameResponse => {
     const coalescedRanges: FileBlameResponse['ranges'] = [];
     for (const range of ranges) {
         const last = coalescedRanges[coalescedRanges.length - 1];
-        if (last && last.hash === range.hash && last.startLine + last.lineCount === range.startLine) {
+        if (last && last.hash === range.hash && last.path === range.path && last.startLine + last.lineCount === range.startLine) {
             last.lineCount += range.lineCount;
         } else {
             coalescedRanges.push({ ...range });

packages/web/src/features/git/schemas.ts

@@ -119,6 +119,7 @@ export const fileBlameRequestSchema = z.object({
 
 export const blameRangeSchema = z.object({
     hash: z.string().describe('The hash of the commit that last modified the lines in this range.'),
+    path: z.string().describe('The file path as it existed at the attributing commit. May differ from the current path due to renames.'),
     startLine: z.number().int().positive().describe('The 1-based line number where the range begins (inclusive).'),
     lineCount: z.number().int().positive().describe('The number of contiguous lines in this range.'),
 });