fix: add script to strip trailing whitespace from templates

Trailing whitespace in .gitignore patterns can cause unexpected
behavior. This script detects and removes trailing whitespace
from template files with dry-run support.

Signed-off-by: Srikanth Patchava <spatchava@meta.com>

Author: srpatcha

scripts/strip_trailing_whitespace.py

@@ -0,0 +1,78 @@
+#!/usr/bin/env python3
+"""
+Strip trailing whitespace from .gitignore template files.
+
+This script fixes trailing whitespace issues in gitignore templates,
+which can cause unexpected behavior in pattern matching.
+"""
+
+import argparse
+import os
+import sys
+
+
+def strip_file(filepath: str, dry_run: bool = False) -> int:
+    """Strip trailing whitespace from a file. Returns number of lines fixed."""
+    with open(filepath, "r", encoding="utf-8", errors="replace") as f:
+        lines = f.readlines()
+
+    fixed_count = 0
+    new_lines = []
+    for line in lines:
+        stripped = line.rstrip() + "\n"
+        if stripped != line:
+            fixed_count += 1
+        new_lines.append(stripped)
+
+    # Ensure file ends with a single newline
+    if new_lines and new_lines[-1] == "\n":
+        pass  # already ends properly
+    elif not new_lines:
+        new_lines = ["\n"]
+
+    if fixed_count > 0 and not dry_run:
+        with open(filepath, "w", encoding="utf-8", newline="") as f:
+            f.writelines(new_lines)
+
+    return fixed_count
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Strip trailing whitespace from .gitignore templates."
+    )
+    parser.add_argument("files", nargs="*", help="Files to process.")
+    parser.add_argument("--repo-root", default=".", help="Repo root directory.")
+    parser.add_argument(
+        "--dry-run", action="store_true", help="Report but do not modify files."
+    )
+    args = parser.parse_args()
+
+    if args.files:
+        targets = args.files
+    else:
+        targets = []
+        for entry in os.listdir(args.repo_root):
+            full = os.path.join(args.repo_root, entry)
+            if os.path.isfile(full) and entry.endswith(".gitignore"):
+                targets.append(full)
+
+    total_fixed = 0
+    for filepath in targets:
+        count = strip_file(filepath, dry_run=args.dry_run)
+        if count > 0:
+            action = "would fix" if args.dry_run else "fixed"
+            print(f"  {action} {count} line(s) in {filepath}")
+            total_fixed += count
+
+    if total_fixed == 0:
+        print("No trailing whitespace found.")
+    else:
+        action = "Would fix" if args.dry_run else "Fixed"
+        print(f"\n{action} {total_fixed} line(s) total.")
+
+    sys.exit(0)
+
+
+if __name__ == "__main__":
+    main()