From cc4fb38e50fd792a322b2d043673c3eb25b3363b Mon Sep 17 00:00:00 2001
From: Thomas Randolph <trandolph@gitlab.com>
Date: Wed, 11 Jun 2025 18:45:51 -0600
Subject: [PATCH 1/2] Handle situation where match line is after target line

The logic for `isExpandDown` is a bit confusing, so this is a
known-good fix.

Changelog: fixed
---
 .../javascripts/diffs/stores/legacy_diffs/actions.js   | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/app/assets/javascripts/diffs/stores/legacy_diffs/actions.js b/app/assets/javascripts/diffs/stores/legacy_diffs/actions.js
index ae2b77ca6ba957..9b78ec4e42b3f8 100644
--- a/app/assets/javascripts/diffs/stores/legacy_diffs/actions.js
+++ b/app/assets/javascripts/diffs/stores/legacy_diffs/actions.js
@@ -1130,6 +1130,7 @@ export function fetchLinkedExpandedLine({ fileHash, oldLine, newLine }) {
   const matchLine = findClosestMatchLine(lines, newLine);
   const { new_pos: matchNewPosition, old_pos: matchOldPosition } = matchLine.meta_data;
   const matchLineIndex = lines.indexOf(matchLine);
+  const targetIsBeforeMatch = newLine < matchNewPosition;
   const linesInBetween = countLinesInBetween(lines, matchLineIndex);
   const isExpandBoth = linesInBetween !== -1 && linesInBetween < 20;
   const previousLine = lines[matchLineIndex - 1];
@@ -1164,6 +1165,15 @@ export function fetchLinkedExpandedLine({ fileHash, oldLine, newLine }) {
     });
   }
 
+  if (targetIsBeforeMatch && isExpandDown && previousLine && newLine < previousLine.new_line) {
+    return loadLines({
+      unfold: true,
+      since: newLine,
+      to: matchNewPosition - 1,
+      bottom: isLastMatchLine,
+    });
+  }
+
   if (!isExpandDown) {
     return loadLines({
       unfold: true,
-- 
GitLab


From 916647e93f7e475e652bb331ebca6576f9aa03db Mon Sep 17 00:00:00 2001
From: Thomas Randolph <trandolph@gitlab.com>
Date: Wed, 11 Jun 2025 21:41:09 -0600
Subject: [PATCH 2/2] Add a test for when the match line is after target line

---
 .../diffs/stores/legacy_diffs/actions_spec.js | 40 +++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/spec/frontend/diffs/stores/legacy_diffs/actions_spec.js b/spec/frontend/diffs/stores/legacy_diffs/actions_spec.js
index edeef3dece4190..9db8e4a0afea3a 100644
--- a/spec/frontend/diffs/stores/legacy_diffs/actions_spec.js
+++ b/spec/frontend/diffs/stores/legacy_diffs/actions_spec.js
@@ -2523,6 +2523,46 @@ describe('legacyDiffs actions', () => {
         });
       });
 
+      it('expands lines upwards when the match line is after the target line', async () => {
+        const linkedFile = {
+          file_hash: 'abc123',
+          context_lines_path: `${TEST_HOST}/linked-file`,
+          highlighted_diff_lines: [
+            { old_line: 250, new_line: 250 },
+            { meta_data: { old_pos: 300, new_pos: 300 } },
+            { old_line: 300, new_line: 300 },
+          ],
+        };
+
+        store.$patch({
+          diffFiles: [linkedFile],
+          linkedFileHash: linkedFile.file_hash,
+        });
+
+        await store.fetchLinkedExpandedLine({
+          fileHash: linkedFile.file_hash,
+          oldLine: 286,
+          newLine: 286,
+        });
+
+        expect(store.loadMoreLines).toHaveBeenCalledWith({
+          endpoint: linkedFile.context_lines_path,
+          fileHash: linkedFile.file_hash,
+          isExpandDown: false,
+          lineNumbers: {
+            oldLineNumber: 300,
+            newLineNumber: 300,
+          },
+          params: {
+            bottom: false,
+            offset: 0,
+            since: 286,
+            to: 299,
+            unfold: true,
+          },
+        });
+      });
+
       it('expands lines at the very bottom', async () => {
         const linkedFile = {
           file_hash: 'abc123',
-- 
GitLab