First pass at adding a hook selector for files that contain a given string

pre_commit/clientlib.py

@@ -60,6 +60,7 @@ MANIFEST_HOOK_DICT = cfgv.Map(
     cfgv.Optional('alias', cfgv.check_string, ''),
 
     cfgv.Optional('files', check_string_regex, ''),
+    cfgv.Optional('files_contain', cfgv.check_string, ''),
     cfgv.Optional('exclude', check_string_regex, '^$'),
     cfgv.Optional('types', cfgv.check_array(check_type_tag), ['file']),
     cfgv.Optional('types_or', cfgv.check_array(check_type_tag), []),

pre_commit/commands/run.py

@@ -2,6 +2,7 @@ import argparse
 import contextlib
 import functools
 import logging
+import mmap
 import os
 import re
 import subprocess
@@ -100,6 +101,22 @@ class Classifier:
                 ret.append(filename)
         return ret
 
+    def files_contain(
+        self,
+        names: Sequence[str],
+        contains: str,
+    ) -> List[str]:
+        if contains == '':
+            return list(names)
+
+        ret = []
+        for filename in names:
+            with open(filename, 'r+') as f:
+                with mmap.mmap(f.fileno(), 0) as mm:
+                    if mm.find(contains.encode()) >= 0:
+                        ret.append(filename)
+        return ret
+
     def filenames_for_hook(self, hook: Hook) -> Tuple[str, ...]:
         names = self.filenames
         names = filter_by_include_exclude(names, hook.files, hook.exclude)
@@ -109,6 +126,10 @@ class Classifier:
             hook.types_or,
             hook.exclude_types,
         )
+        names = self.files_contain(
+            names,
+            hook.files_contain,
+        )
         return tuple(names)
 
     @classmethod

pre_commit/hook.py

@@ -20,6 +20,7 @@ class Hook(NamedTuple):
     language: str
     alias: str
     files: str
+    files_contain: str
     exclude: str
     types: Sequence[str]
     types_or: Sequence[str]

pre_commit/meta_hooks/check_useless_excludes.py

@@ -53,7 +53,9 @@ def check_useless_excludes(config_file: str) -> int:
             types = hook['types']
             types_or = hook['types_or']
             exclude_types = hook['exclude_types']
+            files_contain = hook['files_contain']
             names = classifier.by_types(names, types, types_or, exclude_types)
+            names = classifier.files_contain(names, files_contain)
             include, exclude = hook['files'], hook['exclude']
             if not exclude_matches_any(names, include, exclude):
                 print(

tests/commands/run_test.py

@@ -1028,6 +1028,18 @@ def test_classifier_empty_types_or(tmpdir):
         assert for_file == ['bar']
 
 
+def test_classifier_files_contain(tmpdir):
+    tmpdir.join('ignored').ensure().write('We\nIgnore\nThis\nFile\n')
+    tmpdir.join('matched').ensure().write('We\nMatch\nThis\nFile\n')
+    with tmpdir.as_cwd():
+        classifier = Classifier(('ignored', 'matched'))
+        files_contain = classifier.files_contain(
+            classifier.filenames,
+            contains='Match',
+        )
+        assert files_contain == ['matched']
+
+
 @pytest.fixture
 def some_filenames():
     return (

tests/repository_test.py

@@ -986,6 +986,7 @@ def test_manifest_hooks(tempdir_factory, store):
         exclude='^$',
         exclude_types=[],
         files='',
+        files_contain='',
         id='bash_hook',
         language='script',
         language_version='default',