feat: add gitignore support to file watcher

aider/watch.py

@@ -1,7 +1,9 @@
 from pathlib import Path
-from typing import Set
+from typing import Set, Optional
 
 from watchfiles import watch
+from pathspec import PathSpec
+from pathspec.patterns import GitWildMatchPattern
 
 
 def is_source_file(path: Path) -> bool:
@@ -40,16 +42,37 @@ def is_source_file(path: Path) -> bool:
     return path.suffix.lower() in COMMENT_STYLE_EXTENSIONS
 
 
-def watch_source_files(directory: str) -> Set[str]:
+def load_gitignore(gitignore_path: Path) -> Optional[PathSpec]:
+    """Load and parse a .gitignore file"""
+    if not gitignore_path.exists():
+        return None
+        
+    with open(gitignore_path) as f:
+        patterns = f.readlines()
+    
+    return PathSpec.from_lines(GitWildMatchPattern, patterns)
+
+def watch_source_files(directory: str, gitignore: str = None) -> Set[str]:
     """
     Watch for changes to source files in the given directory and its subdirectories.
     Returns a set of changed file paths whenever changes are detected.
+    
+    Args:
+        directory: Root directory to watch
+        gitignore: Path to .gitignore file (optional)
     """
     root = Path(directory)
+    gitignore_spec = None
+    
+    if gitignore:
+        gitignore_spec = load_gitignore(Path(gitignore))
 
-    # Create a filter function that only accepts source files
+    # Create a filter function that only accepts source files and respects gitignore
     def filter_func(change_type, path):
-        return is_source_file(Path(path))
+        path_obj = Path(path)
+        if gitignore_spec and gitignore_spec.match_file(str(path_obj.relative_to(root))):
+            return False
+        return is_source_file(path_obj)
 
     # Watch the directory for changes
     for changes in watch(root, watch_filter=filter_func):
@@ -61,16 +84,18 @@ def watch_source_files(directory: str) -> Set[str]:
 def main():
     """Example usage of the file watcher"""
     import sys
+    import argparse
+    
+    parser = argparse.ArgumentParser(description="Watch source files for changes")
+    parser.add_argument("directory", help="Directory to watch")
+    parser.add_argument("--gitignore", help="Path to .gitignore file")
+    args = parser.parse_args()
 
-    if len(sys.argv) != 2:
-        print("Usage: python watch.py <directory>")
-        sys.exit(1)
-
-    directory = sys.argv[1]
+    directory = args.directory
     print(f"Watching source files in {directory}...")
 
     try:
-        for changed_files in watch_source_files(directory):
+        for changed_files in watch_source_files(directory, args.gitignore):
             print("\nChanged files:")
             for file in sorted(changed_files):
                 print(f"  {file}")