llm-diff-patcher

A TypeScript library for applying "fuzzy" diffs, particularly designed for LLM-generated code modifications where line numbers may not be accurate.

Installation

``bash
npm install llm-diff-patcher
`

Usage

`typescript
import { applyPatchToFiles } from 'llm-diff-patcher';

// Original source code
const sourceText = function hello() {
console.log("Hello, world!");
return true;
};

// A diff to apply (in unified diff format)
const diffText = @@ -1,4 +1,4 @@
function hello() {
- console.log("Hello, world!");
+ console.log("Hello, universe!");
return true;
};

// Apply the fuzzy diff
const result = applyDiff(sourceText, diffText);

console.log(result);
// Output:
// function hello() {
// console.log("Hello, universe!");
// return true;
// }

// For applying to files in a directory:
const patchResult = applyPatchToFiles(diffText, {
basePath: '/path/to/project',
dryRun: false
});

console.log(Files: ${patchResult.successfulFiles}/${patchResult.totalFiles}, Hunks: ${patchResult.appliedHunks}/${patchResult.totalHunks});
`

Configuration Options

You can customize the behavior with options:

`typescript
// When applying to files
const result = applyPatchToFiles(diffText, {
// Base directory for resolving file paths
basePath: '/path/to/project',

// If true, doesn't actually write to files (default: false)
dryRun: true,

// Minimum number of context lines required for a match
minContextLines: 2,

// Options passed to the underlying diff library
jsDiffApplyPatchOptions: {
// Maximum Levenshtein distance between context in patch and actual file lines
// Higher values allow more fuzzy matches (default: 0)
fuzzFactor: 2,

// Automatically handle different line endings between patch and source file
// (default: true)
autoConvertLineEndings: true,

// Custom function to compare lines for equality when patching
// Allows for very flexible fuzzy matching
compareLine: (lineNumber, line, operation, patchContent) => {

// Custom comparison logic here
// Return true if lines should be considered equal, false otherwise
return line.trim() === patchContent.trim(); // Example: ignore whitespace
}
}
});
`

Why llm-diff-patcher?

Unlike traditional diff tools that require exact line numbers to match, llm-diff-patcher is designed to handle the imprecise nature of diffs generated by Large Language Models (LLMs).

Key benefits:

1. Fuzzy Matching: Applies changes based on context even when line numbers are incorrect
2. Robust Error Handling: Provides detailed information about successful and failed patches
3. Flexible Configuration: Adjust matching strictness to your needs
4. Dry Run Mode: Test patches without modifying files

Use Cases

- Applying code changes suggested by AI assistants like GPT, Claude, or other LLMs
- Implementing code modifications across slightly different versions of files
- Working with diffs that may not have perfect context or line numbers
- Automated code refactoring with LLM-generated patches

API

The library provides several key functions:

- applyPatchToFiles: Apply patch to multiple files in a directory
- applyDiff: Apply a single diff to a string
- parsePatch: Parse a patch string into a structured format
- cleanPatch: Clean up and normalize patch text

Error Handling

The library provides detailed error information to help you understand what went wrong:

`typescript
if (!patchResult.success) {
console.error(Failed to apply patch. Errors:);
patchResult.errors.forEach(error => {
console.error(- ${error.message} (${error.context}));
});
}
``

License

MIT