Better error messages for diffs

src/core/Cline.ts

@@ -1237,20 +1237,25 @@ export class Cline {
 								const originalContent = await fs.readFile(absolutePath, "utf-8")
 
 								// Apply the diff to the original content
-								let newContent = this.diffStrategy?.applyDiff(originalContent, diffContent) ?? false
+								const diffResult = this.diffStrategy?.applyDiff(originalContent, diffContent) ?? {
-								if (newContent === false) {
+									success: false,
+									error: "No diff strategy available"
+								}
+								if (!diffResult.success) {
 									this.consecutiveMistakeCount++
-									await this.say("error", `Unable to apply diff to file - contents are out of sync: ${absolutePath}`)
+									const errorDetails = diffResult.details ? `\n\nDetails:\n${JSON.stringify(diffResult.details, null, 2)}` : ''
-									pushToolResult(`Error applying diff to file: ${absolutePath} - contents are out of sync. Try re-reading the relevant lines of the file and applying the diff again.`)
+									await this.say("error", `Unable to apply diff to file: ${absolutePath}\n${diffResult.error}${errorDetails}`)
+									pushToolResult(`Error applying diff to file: ${absolutePath}\n${diffResult.error}${errorDetails}`)
 									break
 								}
+								const newContent = diffResult.content
 
 								this.consecutiveMistakeCount = 0
 
 								// Show diff view before asking for approval
 								this.diffViewProvider.editType = "modify"
 								await this.diffViewProvider.open(relPath);
-								await this.diffViewProvider.update(newContent, true);
+								await this.diffViewProvider.update(diffResult.content, true);
 								await this.diffViewProvider.scrollToFirstDiff();
 
 								const completeMessage = JSON.stringify({

src/core/diff/strategies/__tests__/search-replace.test.ts

@@ -22,7 +22,10 @@ function hello() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe('function hello() {\n    console.log("hello world")\n}\n')
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe('function hello() {\n    console.log("hello world")\n}\n')
+            }
         })
 
         it('should match content with different surrounding whitespace', () => {
@@ -39,7 +42,10 @@ function example() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe('\nfunction example() {\n    return 43;\n}\n\n')
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe('\nfunction example() {\n    return 43;\n}\n\n')
+            }
         })
 
         it('should match content with different indentation in search block', () => {
@@ -56,7 +62,10 @@ function test() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe('    function test() {\n        return false;\n    }\n')
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe('    function test() {\n        return false;\n    }\n')
+            }
         })
 
         it('should handle tab-based indentation', () => {
@@ -73,7 +82,10 @@ function test() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe("function test() {\n\treturn false;\n}\n")
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe("function test() {\n\treturn false;\n}\n")
+            }
         })
 
         it('should preserve mixed tabs and spaces', () => {
@@ -94,7 +106,10 @@ function test() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe("\tclass Example {\n\t    constructor() {\n\t\tthis.value = 1;\n\t    }\n\t}")
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe("\tclass Example {\n\t    constructor() {\n\t\tthis.value = 1;\n\t    }\n\t}")
+            }
         })
 
         it('should handle additional indentation with tabs', () => {
@@ -112,7 +127,10 @@ function test() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe("\tfunction test() {\n\t\t// Add comment\n\t\treturn false;\n\t}")
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe("\tfunction test() {\n\t\t// Add comment\n\t\treturn false;\n\t}")
+            }
         })
 
         it('should preserve exact indentation characters when adding lines', () => {
@@ -131,7 +149,10 @@ function test() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe("\tfunction test() {\n\t\t// First comment\n\t\t// Second comment\n\t\treturn true;\n\t}")
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe("\tfunction test() {\n\t\t// First comment\n\t\t// Second comment\n\t\treturn true;\n\t}")
+            }
         })
 
         it('should handle Windows-style CRLF line endings', () => {
@@ -148,7 +169,10 @@ function test() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe("function test() {\r\n    return false;\r\n}\r\n")
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe("function test() {\r\n    return false;\r\n}\r\n")
+            }
         })
 
         it('should return false if search content does not match', () => {
@@ -165,7 +189,7 @@ function hello() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe(false)
+            expect(result.success).toBe(false)
         })
 
         it('should return false if diff format is invalid', () => {
@@ -173,7 +197,7 @@ function hello() {
             const diffContent = `test.ts\nInvalid diff format`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe(false)
+            expect(result.success).toBe(false)
         })
 
         it('should handle multiple lines with proper indentation', () => {
@@ -192,7 +216,10 @@ function hello() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe('class Example {\n    constructor() {\n        this.value = 0\n    }\n\n    getValue() {\n        // Add logging\n        console.log("Getting value")\n        return this.value\n    }\n}\n')
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe('class Example {\n    constructor() {\n        this.value = 0\n    }\n\n    getValue() {\n        // Add logging\n        console.log("Getting value")\n        return this.value\n    }\n}\n')
+            }
         })
 
         it('should preserve whitespace exactly in the output', () => {
@@ -209,7 +236,10 @@ function hello() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe("    modified\n        still indented\n    end\n")
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe("    modified\n        still indented\n    end\n")
+            }
         })
 
         it('should preserve indentation when adding new lines after existing content', () => {
@@ -226,7 +256,10 @@ function hello() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe('				onScroll={() => updateHighlights()}\n				onDragOver={(e) => {\n					e.preventDefault()\n					e.stopPropagation()\n				}}')
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe('				onScroll={() => updateHighlights()}\n				onDragOver={(e) => {\n					e.preventDefault()\n					e.stopPropagation()\n				}}')
+            }
         })
 
         it('should handle varying indentation levels correctly', () => {
@@ -264,7 +297,9 @@ class Example {
 >>>>>>> REPLACE`.trim();
         
             const result = strategy.applyDiff(originalContent, diffContent);
-            expect(result).toBe(`
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`
 class Example {
     constructor() {
         this.value = 1;
@@ -275,14 +310,15 @@ class Example {
         }
     }
 }`.trim());
-        });
+            }
+        })
 
         it('should handle mixed indentation styles in the same file', () => {
-    const originalContent = `class Example {
+            const originalContent = `class Example {
     constructor() {
         this.value = 0;
         if (true) {
-        this.init();
+            this.init();
         }
     }
 }`.trim();
@@ -305,7 +341,9 @@ class Example {
 >>>>>>> REPLACE`;
         
             const result = strategy.applyDiff(originalContent, diffContent);
-            expect(result).toBe(`class Example {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`class Example {
     constructor() {
         this.value = 1;
         if (true) {
@@ -314,7 +352,8 @@ class Example {
         }
     }
 }`);
-        });
+            }
+        })
         
         it('should handle Python-style significant whitespace', () => {
             const originalContent = `def example():
@@ -338,17 +377,20 @@ class Example {
 >>>>>>> REPLACE`;
         
             const result = strategy.applyDiff(originalContent, diffContent);
-            expect(result).toBe(`def example():
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`def example():
     if condition:
         do_something()
         while items:
             item = items.pop()
             process(item)
     return True`);
+            }
         });
         
         it('should preserve empty lines with indentation', () => {
-    const originalContent = `function test() {
+            const originalContent = `function test() {
     const x = 1;
     
     if (x) {
@@ -368,7 +410,9 @@ class Example {
 >>>>>>> REPLACE`;
         
             const result = strategy.applyDiff(originalContent, diffContent);
-            expect(result).toBe(`function test() {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`function test() {
     const x = 1;
     
     // Check x
@@ -376,6 +420,7 @@ class Example {
         return true;
     }
 }`);
+            }  
         });
         
         it('should handle indentation when replacing entire blocks', () => {
@@ -406,7 +451,9 @@ class Example {
 >>>>>>> REPLACE`;
         
             const result = strategy.applyDiff(originalContent, diffContent);
-            expect(result).toBe(`class Test {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`class Test {
     method() {
         try {
             if (true) {
@@ -417,6 +464,7 @@ class Example {
         }
     }
 }`);
+            }
         });
 
         it('should handle negative indentation relative to search content', () => {
@@ -438,7 +486,9 @@ class Example {
 >>>>>>> REPLACE`;
         
             const result = strategy.applyDiff(originalContent, diffContent);
-            expect(result).toBe(`class Example {
+            expect(result.success).toBe(true)
+            if (result.success) {
+            expect(result.content).toBe(`class Example {
     constructor() {
         if (true) {
         this.init();
@@ -446,6 +496,7 @@ class Example {
         }
     }
 }`);
+            }
         });
         
         it('should handle extreme negative indentation (no indent)', () => {
@@ -464,13 +515,16 @@ this.init();
 >>>>>>> REPLACE`;
         
             const result = strategy.applyDiff(originalContent, diffContent);
-            expect(result).toBe(`class Example {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`class Example {
     constructor() {
         if (true) {
 this.init();
         }
     }
 }`);
+            }
         });
         
         it('should handle mixed indentation changes in replace block', () => {
@@ -495,7 +549,9 @@ this.init();
 >>>>>>> REPLACE`;
         
             const result = strategy.applyDiff(originalContent, diffContent);
-            expect(result).toBe(`class Example {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`class Example {
     constructor() {
         if (true) {
         this.init();
@@ -504,6 +560,7 @@ this.init();
         }
     }
 }`);
+            }
         });
     })
 
@@ -530,7 +587,10 @@ function getData() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe('function getData() {\n    const data = fetchData();\n    return data.filter(Boolean);\n}\n')
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe('function getData() {\n    const data = fetchData();\n    return data.filter(Boolean);\n}\n')
+            }
         })
 
         it('should not match when content is too different (<90% similar)', () => {
@@ -547,7 +607,7 @@ function processData(data) {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe(false)
+            expect(result.success).toBe(false)
         })
 
         it('should match content with extra whitespace', () => {
@@ -564,7 +624,10 @@ function sum(a, b) {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent)
-            expect(result).toBe('function sum(a, b) {\n    return a + b + 1;\n}')
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe('function sum(a, b) {\n    return a + b + 1;\n}')
+            }
         })
     })
 
@@ -601,7 +664,9 @@ function two() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent, 5, 7)
-            expect(result).toBe(`function one() {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`function one() {
     return 1;
 }
 
@@ -612,6 +677,7 @@ function two() {
 function three() {
     return 3;
 }`)
+            }
         })
 
         it('should find and replace within buffer zone (5 lines before/after)', () => {
@@ -642,7 +708,9 @@ function three() {
             // Even though we specify lines 5-7, it should still find the match at lines 9-11
             // because it's within the 5-line buffer zone
             const result = strategy.applyDiff(originalContent, diffContent, 5, 7)
-            expect(result).toBe(`function one() {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`function one() {
     return 1;
 }
 
@@ -653,6 +721,7 @@ function two() {
 function three() {
     return "three";
 }`)
+            }
         })
 
         it('should not find matches outside search range and buffer zone', () => {
@@ -691,7 +760,7 @@ function five() {
             // Searching around function two() (lines 5-7)
             // function five() is more than 5 lines away, so it shouldn't match
             const result = strategy.applyDiff(originalContent, diffContent, 5, 7)
-            expect(result).toBe(false)
+            expect(result.success).toBe(false)
         })
 
         it('should handle search range at start of file', () => {
@@ -716,13 +785,16 @@ function one() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent, 1, 3)
-            expect(result).toBe(`function one() {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`function one() {
     return "one";
 }
 
 function two() {
     return 2;
 }`)
+            }
         })
 
         it('should handle search range at end of file', () => {
@@ -747,13 +819,16 @@ function two() {
 >>>>>>> REPLACE`
 
             const result = strategy.applyDiff(originalContent, diffContent, 5, 7)
-            expect(result).toBe(`function one() {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`function one() {
     return 1;
 }
 
 function two() {
     return "two";
 }`)
+            }
         })
 
         it('should match specific instance of duplicate code using line numbers', () => {
@@ -790,7 +865,9 @@ function processData(data) {
 
             // Target the second instance of processData
             const result = strategy.applyDiff(originalContent, diffContent, 10, 12)
-            expect(result).toBe(`function processData(data) {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`function processData(data) {
     return data.map(x => x * 2);
 }
 
@@ -808,6 +885,7 @@ function processData(data) {
 function moreStuff() {
     console.log("world");
 }`)
+            }
         })
 
         it('should search from start line to end of file when only start_line is provided', () => {
@@ -837,7 +915,9 @@ function three() {
 
             // Only provide start_line, should search from there to end of file
             const result = strategy.applyDiff(originalContent, diffContent, 8)
-            expect(result).toBe(`function one() {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`function one() {
     return 1;
 }
 
@@ -848,6 +928,7 @@ function two() {
 function three() {
     return "three";
 }`)
+            }
         })
 
         it('should search from start of file to end line when only end_line is provided', () => {
@@ -877,7 +958,9 @@ function one() {
 
             // Only provide end_line, should search from start of file to there
             const result = strategy.applyDiff(originalContent, diffContent, undefined, 4)
-            expect(result).toBe(`function one() {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`function one() {
     return "one";
 }
 
@@ -888,6 +971,7 @@ function two() {
 function three() {
     return 3;
 }`)
+            }
         })
 
         it('should prioritize exact line match over expanded search', () => {
@@ -921,7 +1005,9 @@ function process() {
             // Should match the second instance exactly at lines 10-12
             // even though the first instance at 6-8 is within the expanded search range
             const result = strategy.applyDiff(originalContent, diffContent, 10, 12)
-            expect(result).toBe(`
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`
 function one() {
     return 1;
 }
@@ -937,7 +1023,8 @@ function process() {
 function two() {
     return 2;
 }`)
-            })
+            }
+        })
 
         it('should fall back to expanded search only if exact match fails', () => {
             const originalContent = `
@@ -966,7 +1053,9 @@ function process() {
             // Specify wrong line numbers (3-5), but content exists at 6-8
             // Should still find and replace it since it's within the expanded range
             const result = strategy.applyDiff(originalContent, diffContent, 3, 5)
-            expect(result).toBe(`function one() {
+            expect(result.success).toBe(true)
+            if (result.success) {
+                expect(result.content).toBe(`function one() {
     return 1;
 }
 
@@ -977,6 +1066,7 @@ function process() {
 function two() {
     return 2;
 }`)
+            }
         })
     })
 

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

@@ -1,4 +1,4 @@
-import { DiffStrategy } from "../types"
+import { DiffStrategy, DiffResult } from "../types"
 
 function levenshteinDistance(a: string, b: string): number {
     const matrix: number[][] = [];
@@ -115,11 +115,20 @@ Your search/replace content here
 </apply_diff>`
     }
 
-    applyDiff(originalContent: string, diffContent: string, startLine?: number, endLine?: number): string | false {
+    applyDiff(originalContent: string, diffContent: string, startLine?: number, endLine?: number): DiffResult {
         // Extract the search and replace blocks
         const match = diffContent.match(/<<<<<<< SEARCH\n([\s\S]*?)\n=======\n([\s\S]*?)\n>>>>>>> REPLACE/);
         if (!match) {
-            return false;
+            // Log detailed format information
+            console.log('Invalid Diff Format Debug:', {
+                expectedFormat: "<<<<<<< SEARCH\\n[search content]\\n=======\\n[replace content]\\n>>>>>>> REPLACE",
+                tip: "Make sure to include both SEARCH and REPLACE sections with correct markers"
+            });
+
+            return {
+                success: false,
+                error: "Invalid diff format - missing required SEARCH/REPLACE sections"
+            };
         }
 
         const [_, searchContent, replaceContent] = match;
@@ -135,12 +144,26 @@ Your search/replace content here
         // First try exact line range if provided
         let matchIndex = -1;
         let bestMatchScore = 0;
+        let bestMatchContent = "";
         
         if (startLine !== undefined && endLine !== undefined) {
             // Convert to 0-based index
             const exactStartIndex = startLine - 1;
             const exactEndIndex = endLine - 1;
 
+            if (exactStartIndex < 0 || exactEndIndex >= originalLines.length) {
+                // Log detailed debug information
+                console.log('Invalid Line Range Debug:', {
+                    requestedRange: { start: startLine, end: endLine },
+                    fileBounds: { start: 1, end: originalLines.length }
+                });
+
+                return {
+                    success: false,
+                    error: `Line range ${startLine}-${endLine} is invalid (file has ${originalLines.length} lines)`,
+                };
+            }
+
             // Check exact range first
             const originalChunk = originalLines.slice(exactStartIndex, exactEndIndex + 1).join('\n');
             const searchChunk = searchLines.join('\n');
@@ -149,6 +172,7 @@ Your search/replace content here
             if (similarity >= this.fuzzyThreshold) {
                 matchIndex = exactStartIndex;
                 bestMatchScore = similarity;
+                bestMatchContent = originalChunk;
             }
         }
 
@@ -177,13 +201,26 @@ Your search/replace content here
                 if (similarity > bestMatchScore) {
                     bestMatchScore = similarity;
                     matchIndex = i;
+                    bestMatchContent = originalChunk;
                 }
             }
         }
 
         // Require similarity to meet threshold
         if (matchIndex === -1 || bestMatchScore < this.fuzzyThreshold) {
-            return false;
+            const searchChunk = searchLines.join('\n');
+            // Log detailed debug information to console
+            console.log('Search/Replace Debug Info:', {
+                similarity: bestMatchScore,
+                threshold: this.fuzzyThreshold,
+                searchContent: searchChunk,
+                bestMatch: bestMatchContent || undefined
+            });
+
+            return {
+                success: false,
+                error: `No sufficiently similar match found${startLine !== undefined ? ` near lines ${startLine}-${endLine}` : ''} (${Math.round(bestMatchScore * 100)}% similar, needs ${Math.round(this.fuzzyThreshold * 100)}%)`
+            };
         }
 
         // Get the matched lines from the original content
@@ -229,6 +266,10 @@ Your search/replace content here
         const beforeMatch = originalLines.slice(0, matchIndex);
         const afterMatch = originalLines.slice(matchIndex + searchLines.length);
         
-        return [...beforeMatch, ...indentedReplaceLines, ...afterMatch].join(lineEnding);
+        const finalContent = [...beforeMatch, ...indentedReplaceLines, ...afterMatch].join(lineEnding);
+        return {
+            success: true,
+            content: finalContent
+        };
     }
-}
+}

src/core/diff/strategies/unified.ts

@@ -1,5 +1,5 @@
 import { applyPatch } from "diff"
-import { DiffStrategy } from "../types"
+import { DiffStrategy, DiffResult } from "../types"
 
 export class UnifiedDiffStrategy implements DiffStrategy {
     getToolDescription(cwd: string): string {
@@ -108,7 +108,30 @@ Your diff here
 </apply_diff>`
     }
 
-    applyDiff(originalContent: string, diffContent: string): string | false {
+    applyDiff(originalContent: string, diffContent: string): DiffResult {
-        return applyPatch(originalContent, diffContent) as string | false
+        try {
+            const result = applyPatch(originalContent, diffContent)
+            if (result === false) {
+                return {
+                    success: false,
+                    error: "Failed to apply unified diff - patch rejected",
+                    details: {
+                        searchContent: diffContent
+                    }
+                }
+            }
+            return {
+                success: true,
+                content: result
+            }
+        } catch (error) {
+            return {
+                success: false,
+                error: `Error applying unified diff: ${error.message}`,
+                details: {
+                    searchContent: diffContent
+                }
+            }
+        }
     }
 }

src/core/diff/types.ts

@@ -1,6 +1,17 @@
 /**
  * Interface for implementing different diff strategies
  */
+
+export type DiffResult = 
+  | { success: true; content: string }
+  | { success: false; error: string; details?: { 
+      similarity?: number;
+      threshold?: number;
+      matchedRange?: { start: number; end: number };
+      searchContent?: string;
+      bestMatch?: string;
+    }};
+
 export interface DiffStrategy {
     /**
      * Get the tool description for this diff strategy
@@ -15,7 +26,7 @@ export interface DiffStrategy {
      * @param diffContent The diff content in the strategy's format
      * @param startLine Optional line number where the search block starts. If not provided, searches the entire file.
      * @param endLine Optional line number where the search block ends. If not provided, searches the entire file.
-     * @returns The new content after applying the diff, or false if the diff could not be applied
+     * @returns A DiffResult object containing either the successful result or error details
      */
-    applyDiff(originalContent: string, diffContent: string, startLine?: number, endLine?: number): string | false
+    applyDiff(originalContent: string, diffContent: string, startLine?: number, endLine?: number): DiffResult
 }