Utilize pipelining of grep_search -> read_file to eliminate turns (#19574)

packages/core/src/tools/diff-utils.ts

@@ -0,0 +1,75 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as Diff from 'diff';
+
+/**
+ * Generates a snippet of the diff between two strings, including a few lines of context around the changes.
+ */
+export function getDiffContextSnippet(
+  originalContent: string,
+  newContent: string,
+  contextLines = 5,
+): string {
+  if (!originalContent) {
+    return newContent;
+  }
+
+  const changes = Diff.diffLines(originalContent, newContent);
+  const newLines = newContent.split(/\r?\n/);
+  const ranges: Array<{ start: number; end: number }> = [];
+  let newLineIdx = 0;
+
+  for (const change of changes) {
+    if (change.added) {
+      ranges.push({ start: newLineIdx, end: newLineIdx + (change.count ?? 0) });
+      newLineIdx += change.count ?? 0;
+    } else if (change.removed) {
+      ranges.push({ start: newLineIdx, end: newLineIdx });
+    } else {
+      newLineIdx += change.count ?? 0;
+    }
+  }
+
+  if (ranges.length === 0) {
+    return newContent;
+  }
+
+  const expandedRanges = ranges.map((r) => ({
+    start: Math.max(0, r.start - contextLines),
+    end: Math.min(newLines.length, r.end + contextLines),
+  }));
+  expandedRanges.sort((a, b) => a.start - b.start);
+  const mergedRanges: Array<{ start: number; end: number }> = [];
+
+  if (expandedRanges.length > 0) {
+    let current = expandedRanges[0];
+    for (let i = 1; i < expandedRanges.length; i++) {
+      const next = expandedRanges[i];
+      if (next.start <= current.end) {
+        current.end = Math.max(current.end, next.end);
+      } else {
+        mergedRanges.push(current);
+        current = next;
+      }
+    }
+    mergedRanges.push(current);
+  }
+
+  const outputParts: string[] = [];
+  let lastEnd = 0;
+
+  for (const range of mergedRanges) {
+    if (range.start > lastEnd) outputParts.push('...');
+    outputParts.push(newLines.slice(range.start, range.end).join('\n'));
+    lastEnd = range.end;
+  }
+
+  if (lastEnd < newLines.length) {
+    outputParts.push('...');
+  }
+  return outputParts.join('\n');
+}