lint.py: add option to only check tracked files

.github/workflows/build.yml

@@ -147,7 +147,7 @@ jobs:
         # don't need tags here
     - name: Check whitespace
       run: |
-        python ci/lint.py --github-actions
+        python ci/lint.py --git-only --github-actions
     - name: Check Authors.rst
       if: success() || failure()
       run: |

ci/lint.py

@@ -3,6 +3,7 @@ import argparse
 import fnmatch
 import re
 import os
+import subprocess
 import sys
 
 DFHACK_ROOT = os.path.normpath(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
@@ -109,6 +110,21 @@ class TabLinter(Linter):
 
 linters = [cls() for cls in Linter.__subclasses__() if not cls.ignore]
 
+def walk_all(root_path):
+    for cur, dirnames, filenames in os.walk(root_path):
+        for filename in filenames:
+            full_path = os.path.join(cur, filename)
+            yield full_path
+
+def walk_git_files(root_path):
+    p = subprocess.Popen(['git', '-C', root_path, 'ls-files', root_path], stdout=subprocess.PIPE)
+    for line in p.stdout.readlines():
+        path = line.decode('utf-8').strip()
+        full_path = os.path.join(root_path, path)
+        yield full_path
+    if p.wait() != 0:
+        raise RuntimeError('git exited with %r' % p.returncode)
+
 def main(args):
     root_path = os.path.abspath(args.path)
     if not os.path.exists(args.path):
@@ -118,9 +134,11 @@ def main(args):
     check_patterns = load_pattern_files(args.check_patterns)
     ignore_patterns = load_pattern_files(args.ignore_patterns)
 
-    for cur, dirnames, filenames in os.walk(root_path):
-        for filename in filenames:
-            full_path = os.path.join(cur, filename)
+    walk_iter = walk_all
+    if args.git_only:
+        walk_iter = walk_git_files
+
+    for full_path in walk_iter(root_path):
         rel_path = full_path.replace(root_path, '').replace('\\', '/').lstrip('/')
         if not valid_file(rel_path, check_patterns, ignore_patterns):
             continue
@@ -163,6 +181,8 @@ if __name__ == '__main__':
         help='Path to scan (default: current directory)')
     parser.add_argument('--fix', action='store_true',
         help='Attempt to modify files in-place to fix identified issues')
+    parser.add_argument('--git-only', action='store_true',
+        help='Only check files tracked by git')
     parser.add_argument('--github-actions', action='store_true',
         help='Enable GitHub Actions workflow command output')
     parser.add_argument('-v', '--verbose', action='store_true',