feat: add --staged flag to lint only files staged in the index

src/omegaup_hook_tools/git_tools.py

@@ -101,6 +101,17 @@ def _validate_args(args: argparse.Namespace, files: Sequence[Text]) -> bool:
                    f'with `commits` or `files`.{COLORS.NORMAL}'),
                   file=sys.stderr)
             return False
+    if args.staged:
+        if args.all_files:
+            print((f'{COLORS.FAIL}--staged is incompatible '
+                   f'with --all-files.{COLORS.NORMAL}'),
+                  file=sys.stderr)
+            return False
+        if args.commits or files:
+            print((f'{COLORS.FAIL}--staged is incompatible '
+                   f'with `commits` or `files`.{COLORS.NORMAL}'),
+                  file=sys.stderr)
+            return False
     if len(args.commits) not in (0, 1, 2):
         # args.commits can never be empty since its default value is ['HEAD'],
         # but the user can specify zero commits.
@@ -122,6 +133,32 @@ def _get_all_files() -> Iterator[bytes]:
             yield path
 
 
+def _get_staged_files() -> Iterator[bytes]:
+    '''Returns the list of files that are staged in the index.'''
+    cmd = ['/usr/bin/git', 'diff-index', '-z', '--diff-filter=d',
+           '--cached', 'HEAD']
+    tokens = subprocess.run(cmd,
+                            check=True,
+                            stdout=subprocess.PIPE,
+                            cwd=root_dir()).stdout.split(b'\x00')
+    idx = 0
+    while idx < len(tokens) - 1:
+        match = GIT_DIFF_TREE_PATTERN.match(tokens[idx])
+        assert match, tokens[idx]
+        filemode, status = match.groups()
+        if filemode == GIT_DIRECTORY_ENTRY_MODE:
+            idx += 2
+            continue
+        src = tokens[idx + 1]
+        if status in (b'C', b'R'):
+            dest = tokens[idx + 2]
+            idx += 3
+            yield dest
+        else:
+            idx += 2
+            yield src
+
+
 def _get_changed_files(commits: List[Text]) -> Iterator[bytes]:
     ''' Returns the list of files that were modified in the specified range.'''
 
@@ -168,6 +205,8 @@ def _files_to_consider(args: argparse.Namespace) -> List[Text]:
     # Get all files in the latter commit.
     if args.all_files:
         result = _get_all_files()
+    elif args.staged:
+        result = _get_staged_files()
     else:
         result = _get_changed_files(args.commits)
 
@@ -208,6 +247,13 @@ def prompt(question: Text, default: bool = True) -> bool:
 def file_contents(args: argparse.Namespace, root: Text,
                   filename: Text) -> bytes:
     '''Returns contents of |filename| at the revision specified by |args|.'''
+    if getattr(args, 'staged', False):
+        # When --staged is used, read the version of the file from the index.
+        return subprocess.run(
+            ['/usr/bin/git', 'show', f':{filename}'],
+            check=True,
+            stdout=subprocess.PIPE,
+            cwd=root).stdout
     if len(args.commits) in (0, 1):
         # Zero or one commits (where the former is a shorthand for 'HEAD')
         # always diff against the current contents of the file in the
@@ -259,6 +305,11 @@ def parse_arguments(
     validate_parser.add_argument(
         '--all-files', action='store_true',
         help='Considers all files. Incompatible with `commits` and `files`')
+    validate_parser.add_argument(
+        '--staged', action='store_true',
+        help=('Only considers files staged in the index '
+              '(git diff --cached). Incompatible with '
+              '--all-files, `commits`, and `files`'))
     validate_parser.add_argument(
         'commits',
         metavar='[commit [commit ...]] [--] [file [file ...]]',
@@ -276,6 +327,11 @@ def parse_arguments(
         '--all-files', action='store_true',
         help=('Considers all files. '
               'Incompatible with `commits` and `files`'))
+    fix_parser.add_argument(
+        '--staged', action='store_true',
+        help=('Only considers files staged in the index '
+              '(git diff --cached). Incompatible with '
+              '--all-files, `commits`, and `files`'))
     fix_parser.add_argument(
         'commits',
         metavar='[commit [commit ...]] [--] [file [file ...]]',