Add a Claude hook for formatting (#17033)

Inspired by
https://github.com/oven-sh/bun/blob/main/.claude/hooks/pre-bash-zig-build.js

This has been driving me pretty crazy and the fix is easy enough.

.claude/hooks/post-edit-format.py

@@ -0,0 +1,81 @@
+# /// script
+# requires-python = ">=3.12"
+# dependencies = []
+# ///
+
+"""Post-edit hook to auto-format files after Claude edits."""
+
+import json
+import subprocess
+import sys
+from pathlib import Path
+
+
+def format_rust(file_path: str, cwd: str) -> None:
+    """Format Rust files with cargo fmt."""
+    try:
+        subprocess.run(
+            ["cargo", "fmt", "--", file_path],
+            cwd=cwd,
+            capture_output=True,
+        )
+    except FileNotFoundError:
+        pass
+
+
+def format_python(file_path: str, cwd: str) -> None:
+    """Format Python files with ruff."""
+    try:
+        subprocess.run(
+            ["uvx", "ruff", "format", file_path],
+            cwd=cwd,
+            capture_output=True,
+        )
+    except FileNotFoundError:
+        pass
+
+
+def format_prettier(file_path: str, cwd: str, prose_wrap: bool = False) -> None:
+    """Format files with prettier."""
+    args = ["npx", "prettier", "--write"]
+    if prose_wrap:
+        args.extend(["--prose-wrap", "always"])
+    args.append(file_path)
+    try:
+        subprocess.run(args, cwd=cwd, capture_output=True)
+    except FileNotFoundError:
+        pass
+
+
+def main() -> None:
+    import os
+
+    input_data = json.load(sys.stdin)
+
+    tool_name = input_data.get("tool_name")
+    tool_input = input_data.get("tool_input", {})
+    file_path = tool_input.get("file_path")
+
+    # Only process Write, Edit, and MultiEdit tools
+    if tool_name not in ("Write", "Edit", "MultiEdit"):
+        return
+
+    if not file_path:
+        return
+
+    cwd = os.environ.get("CLAUDE_PROJECT_DIR", os.getcwd())
+    path = Path(file_path)
+    ext = path.suffix
+
+    if ext == ".rs":
+        format_rust(file_path, cwd)
+    elif ext in (".py", ".pyi"):
+        format_python(file_path, cwd)
+    elif ext in (".json5", ".yaml", ".yml"):
+        format_prettier(file_path, cwd)
+    elif ext == ".md":
+        format_prettier(file_path, cwd, prose_wrap=True)
+
+
+if __name__ == "__main__":
+    main()

.claude/settings.json

@@ -0,0 +1,15 @@
+{
+  "hooks": {
+    "PostToolUse": [
+      {
+        "matcher": "Edit|Write|MultiEdit",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "uv run .claude/hooks/post-edit-format.py"
+          }
+        ]
+      }
+    ]
+  }
+}