feat: preserve EOL in files (#16087)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Adib234 <30782825+Adib234@users.noreply.github.com>
Co-authored-by: Jack Wotherspoon <jackwoth@google.com>

packages/core/src/utils/editCorrector.test.ts

@@ -639,6 +639,33 @@ describe('editCorrector', () => {
         expect(result.params).toEqual(originalParams);
       });
     });
+
+    describe('Scenario Group 7: Trimming with Newline Preservation', () => {
+      it('Test 7.1: should preserve trailing newlines in new_string when trimming is applied', async () => {
+        const currentContent = '  find me'; // Matches old_string initially
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: '  find me', // Matches, but has whitespace to trim
+          new_string: '  replaced\n\n', // Needs trimming but preserve newlines
+        };
+
+        const result = await ensureCorrectEdit(
+          '/test/file.txt',
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          mockBaseLlmClientInstance,
+          abortSignal,
+          false,
+        );
+
+        // old_string should be trimmed to 'find me' because 'find me' also exists uniquely in '  find me'
+        expect(result.params.old_string).toBe('find me');
+        // new_string should be trimmed of spaces but keep ALL newlines
+        expect(result.params.new_string).toBe('replaced\n\n');
+        expect(result.occurrences).toBe(1);
+      });
+    });
   });
 
   describe('ensureCorrectFileContent', () => {

packages/core/src/utils/editCorrector.ts

@@ -689,13 +689,20 @@ Return ONLY the corrected string in the specified JSON format with the key 'corr
   }
 }
 
+function trimPreservingTrailingNewline(str: string): string {
+  const trimmedEnd = str.trimEnd();
+  const trailingWhitespace = str.slice(trimmedEnd.length);
+  const trailingNewlines = trailingWhitespace.replace(/[^\r\n]/g, '');
+  return str.trim() + trailingNewlines;
+}
+
 function trimPairIfPossible(
   target: string,
   trimIfTargetTrims: string,
   currentContent: string,
   expectedReplacements: number,
 ) {
-  const trimmedTargetString = target.trim();
+  const trimmedTargetString = trimPreservingTrailingNewline(target);
   if (target.length !== trimmedTargetString.length) {
     const trimmedTargetOccurrences = countOccurrences(
       currentContent,
@@ -703,7 +710,8 @@ function trimPairIfPossible(
     );
 
     if (trimmedTargetOccurrences === expectedReplacements) {
-      const trimmedReactiveString = trimIfTargetTrims.trim();
+      const trimmedReactiveString =
+        trimPreservingTrailingNewline(trimIfTargetTrims);
       return {
         targetString: trimmedTargetString,
         pair: trimmedReactiveString,

packages/core/src/utils/textUtils.ts

@@ -54,6 +54,17 @@ export function isBinary(
   return false;
 }
 
+/**
+ * Detects the line ending style of a string.
+ * @param content The string content to analyze.
+ * @returns '\r\n' for Windows-style, '\n' for Unix-style.
+ */
+export function detectLineEnding(content: string): '\r\n' | '\n' {
+  // If a Carriage Return is found, assume Windows-style endings.
+  // This is a simple but effective heuristic.
+  return content.includes('\r\n') ? '\r\n' : '\n';
+}
+
 /**
  * Truncates a string to a maximum length, appending a suffix if truncated.
  * @param str The string to truncate.