add --negate flag to pygrep

pre_commit/languages/pygrep.py

@@ -1,6 +1,7 @@
 import argparse
 import re
 import sys
+from typing import NamedTuple
 from typing import Optional
 from typing import Pattern
 from typing import Sequence
@@ -45,6 +46,46 @@ def _process_filename_at_once(pattern: Pattern[bytes], filename: str) -> int:
     return retv
 
 
+def _process_filename_by_line_negated(
+        pattern: Pattern[bytes],
+        filename: str,
+) -> int:
+    with open(filename, 'rb') as f:
+        for line in f:
+            if pattern.search(line):
+                return 0
+        else:
+            output.write_line(filename)
+            return 1
+
+
+def _process_filename_at_once_negated(
+        pattern: Pattern[bytes],
+        filename: str,
+) -> int:
+    with open(filename, 'rb') as f:
+        contents = f.read()
+    match = pattern.search(contents)
+    if match:
+        return 0
+    else:
+        output.write_line(filename)
+        return 1
+
+
+class Choice(NamedTuple):
+    multiline: bool
+    negate: bool
+
+
+FNS = {
+    Choice(multiline=True, negate=True): _process_filename_at_once_negated,
+    Choice(multiline=True, negate=False): _process_filename_at_once,
+    Choice(multiline=False, negate=True): _process_filename_by_line_negated,
+    Choice(multiline=False, negate=False): _process_filename_by_line,
+}
+
+
 def run_hook(
         hook: Hook,
         file_args: Sequence[str],
@@ -64,6 +105,7 @@ def main(argv: Optional[Sequence[str]] = None) -> int:
     )
     parser.add_argument('-i', '--ignore-case', action='store_true')
     parser.add_argument('--multiline', action='store_true')
+    parser.add_argument('--negate', action='store_true')
     parser.add_argument('pattern', help='python regex pattern.')
     parser.add_argument('filenames', nargs='*')
     args = parser.parse_args(argv)
@@ -75,11 +117,9 @@ def main(argv: Optional[Sequence[str]] = None) -> int:
     pattern = re.compile(args.pattern.encode(), flags)
 
     retv = 0
+    process_fn = FNS[Choice(multiline=args.multiline, negate=args.negate)]
     for filename in args.filenames:
-        if args.multiline:
-            retv |= _process_filename_at_once(pattern, filename)
-        else:
-            retv |= _process_filename_by_line(pattern, filename)
+        retv |= process_fn(pattern, filename)
     return retv