fix: compute first changed diff line from patch hunks

Uses hunk contents to find the first modified line instead of the hunk start Handles added, removed, and binary-only patches more accurately Adds tests for patch parsing edge cases
2026-07-06 01:26:56 +03:00
parent 0f3b7f96c2
commit d8f0ef074b
3 changed files with 67 additions and 20 deletions
@@ -0,0 +1,36 @@
+export const getFirstChangedModifiedLineFromPatch = (patch: string): number | null => {
+  if (!patch) {
+    return null;
+  }
+
+  const lines = patch.split('\n');
+  let modifiedLine: number | null = null;
+
+  for (const line of lines) {
+    const hunkMatch = line.match(/^@@\s*-\d+(?:,\d+)?\s+\+(\d+)(?:,\d+)?\s*@@/);
+    if (hunkMatch) {
+      const parsed = Number.parseInt(hunkMatch[1] ?? '', 10);
+      modifiedLine = Number.isFinite(parsed) && parsed >= 1 ? parsed : null;
+      continue;
+    }
+
+    if (modifiedLine === null) {
+      continue;
+    }
+
+    if (line.startsWith(' ')) {
+      modifiedLine += 1;
+      continue;
+    }
+
+    if (line.startsWith('+')) {
+      return modifiedLine;
+    }
+
+    if (line.startsWith('-')) {
+      return Math.max(1, modifiedLine);
+    }
+  }
+
+  return null;
+};