Better error messages for diffs

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
+        };
     }
-}
+}