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fix: enhance null edit detection for Gemini models
- Add detailed error messages when search and replace content are identical - Provide clear guidance on common causes (model hallucination, copy/paste errors) - Add comprehensive tests for null edit detection - Help AI models (especially Gemini) avoid producing phantom edits Fixes #7360
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‎src/core/diff/strategies/__tests__/null-edit-detection.spec.ts‎

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import { MultiSearchReplaceDiffStrategy } from "../multi-search-replace"
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describe("null edit detection", () => {
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let strategy: MultiSearchReplaceDiffStrategy
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beforeEach(() => {
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strategy = new MultiSearchReplaceDiffStrategy()
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})
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it("should detect and reject null edits (identical search and replace)", async () => {
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const originalContent = 'function hello() {\n console.log("hello")\n}\n'
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const diffContent = [
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"<<<<<<< SEARCH",
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"function hello() {",
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' console.log("hello")',
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"}",
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"=======",
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"function hello() {",
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' console.log("hello")',
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"}",
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">>>>>>> REPLACE",
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].join("\n")
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const result = await strategy.applyDiff(originalContent, diffContent)
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expect(result.success).toBe(false)
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if (!result.success && result.failParts && result.failParts.length > 0) {
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const firstError = result.failParts[0]
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if (!firstError.success && firstError.error) {
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expect(firstError.error).toContain("NULL EDIT DETECTED")
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expect(firstError.error).toContain("Search and replace content are identical")
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expect(firstError.error).toContain("This is a common issue with AI models (especially Gemini)")
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expect(firstError.error).toContain("Model hallucination")
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}
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}
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})
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it("should detect null edits in multi-block diffs", async () => {
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const originalContent =
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'function hello() {\n console.log("hello")\n}\nfunction world() {\n return "world"\n}'
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const diffContent = [
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"<<<<<<< SEARCH",
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"function hello() {",
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' console.log("hello")',
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"}",
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"=======",
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"function hello() {",
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' console.log("hello world")',
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"}",
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">>>>>>> REPLACE",
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"",
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"<<<<<<< SEARCH",
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"function world() {",
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' return "world"',
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"}",
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"=======",
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"function world() {",
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' return "world"',
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"}",
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">>>>>>> REPLACE",
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].join("\n")
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const result = await strategy.applyDiff(originalContent, diffContent)
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// Should partially succeed but report the null edit
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expect(result.success).toBe(true)
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if (result.success) {
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expect(result.failParts).toBeDefined()
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if (result.failParts && result.failParts[0] && !result.failParts[0].success) {
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expect(result.failParts[0].error).toContain("NULL EDIT DETECTED")
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}
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}
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})
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it("should detect null edits with line numbers", async () => {
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const originalContent = "function test() {\n return true;\n}\n"
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const diffContent = [
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"<<<<<<< SEARCH",
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":start_line:1",
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"-------",
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"function test() {",
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" return true;",
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"}",
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"=======",
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"function test() {",
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" return true;",
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"}",
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">>>>>>> REPLACE",
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].join("\n")
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const result = await strategy.applyDiff(originalContent, diffContent)
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expect(result.success).toBe(false)
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if (!result.success && result.failParts && result.failParts.length > 0) {
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const firstError = result.failParts[0]
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if (!firstError.success && firstError.error) {
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expect(firstError.error).toContain("NULL EDIT DETECTED")
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expect(firstError.error).toContain("phantom")
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expect(firstError.error).toContain("Ensure the REPLACE block contains the actual modified content")
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}
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}
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})
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it("should not trigger null edit detection for legitimate empty replacements (deletions)", async () => {
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const originalContent = "function test() {\n // Remove this comment\n return true;\n}\n"
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const diffContent = ["<<<<<<< SEARCH", " // Remove this comment", "=======", ">>>>>>> REPLACE"].join("\n")
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const result = await strategy.applyDiff(originalContent, diffContent)
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expect(result.success).toBe(true)
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// Should not contain null edit error
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if (!result.success && result.error) {
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expect(result.error).not.toContain("NULL EDIT DETECTED")
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}
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})
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it("should not trigger for actual changes even if similar", async () => {
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const originalContent = "function test() {\n return true;\n}\n"
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const diffContent = [
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"<<<<<<< SEARCH",
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"function test() {",
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" return true;",
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"}",
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"=======",
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"function test() {",
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" return false;",
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"}",
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">>>>>>> REPLACE",
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].join("\n")
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const result = await strategy.applyDiff(originalContent, diffContent)
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expect(result.success).toBe(true)
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// Should not contain null edit error
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if (!result.success && result.error) {
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expect(result.error).not.toContain("NULL EDIT DETECTED")
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}
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})
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})

‎src/core/diff/strategies/multi-file-search-replace.ts‎

Lines changed: 10 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -515,10 +515,17 @@ Each file requires its own path, start_line, and diff elements.
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diffResults.push({
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success: false,
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error:
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`Search and replace content are identical - no changes would be made\n\n` +
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`NULL EDIT DETECTED: Search and replace content are identical - no changes would be made\n\n` +
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`This is a common issue with AI models (especially Gemini) producing "phantom" edits.\n\n` +
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`Debug Info:\n` +
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`- Search and replace must be different to make changes\n` +
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`- Use read_file to verify the content you want to change`,
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`- The SEARCH block and REPLACE block contain exactly the same content\n` +
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`- This means the edit would have zero effect on the file\n` +
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`- To fix: Ensure the REPLACE block contains the actual modified content\n` +
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`- Use read_file to verify the current file content before making changes\n\n` +
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`Common causes:\n` +
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`1. Model hallucination - thinking it made changes when it didn't\n` +
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`2. Incorrect copy/paste of content between blocks\n` +
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`3. Missing the actual modification in the REPLACE block`,
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})
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continue
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}

‎src/core/diff/strategies/multi-search-replace.ts‎

Lines changed: 10 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -432,10 +432,17 @@ Only use a single line of '=======' between search and replacement content, beca
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diffResults.push({
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success: false,
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error:
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`Search and replace content are identical - no changes would be made\n\n` +
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`NULL EDIT DETECTED: Search and replace content are identical - no changes would be made\n\n` +
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`This is a common issue with AI models (especially Gemini) producing "phantom" edits.\n\n` +
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`Debug Info:\n` +
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`- Search and replace must be different to make changes\n` +
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`- Use read_file to verify the content you want to change`,
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`- The SEARCH block and REPLACE block contain exactly the same content\n` +
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`- This means the edit would have zero effect on the file\n` +
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`- To fix: Ensure the REPLACE block contains the actual modified content\n` +
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`- Use read_file to verify the current file content before making changes\n\n` +
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`Common causes:\n` +
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`1. Model hallucination - thinking it made changes when it didn't\n` +
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`2. Incorrect copy/paste of content between blocks\n` +
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`3. Missing the actual modification in the REPLACE block`,
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})
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continue
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}

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