Add missing init hook

http://python-notes.curiousefficiency.org/en/latest/python_concepts/import_traps.html#the-init-py-trap

.pre-commit-hooks.yaml

@@ -64,6 +64,20 @@
     entry: check-merge-conflict
     language: python
     types: [text]
+-   id: check-missing-inits
+    name: Find directories with missing __init__ files
+    description: |-
+        Verify that all Python directories contain an __init__.py
+
+        Although __init__.py files are not required on Python 3.3+, omitting them in
+        one directory while having them in another directory will break in confusing
+        and unexpected ways:
+
+        http://python-notes.curiousefficiency.org/en/latest/python_concepts/import_traps.html#the-init-py-trap
+    entry: check-missing-inits
+    language: python
+    require_serial: true
+    files: .*\.py$
 -   id: check-symlinks
     name: Check for broken symlinks
     description: Checks for symlinks which do not point to anything.

README.md

@@ -41,6 +41,7 @@ Add this to your `.pre-commit-config.yaml`
   proper shebang.
 - `check-json` - Attempts to load all json files to verify syntax.
 - `check-merge-conflict` - Check for files that contain merge conflict strings.
+- `check-missing-inits` - Checks for missing `__init__.py` files in any directory containing Python files.
 - `check-symlinks` - Checks for symlinks which do not point to anything.
 - `check-toml` - Attempts to load all TOML files to verify syntax.
 - `check-vcs-permalinks` - Ensures that links to vcs websites are permalinks.

pre_commit_hooks/check_missing_inits.py

@@ -0,0 +1,25 @@
+import os
+from argparse import ArgumentParser
+from typing import Optional
+from typing import Sequence
+
+
+def main(argv=None):  # type: (Optional[Sequence[str]]) -> int
+    parser = ArgumentParser()
+    parser.add_argument('filenames', nargs='*', help='Filenames to check')
+    args = parser.parse_args(argv)
+
+    directories = {os.path.dirname(f) for f in args.filenames}
+    missing_dirs = set()
+    for d in directories:
+        if not os.path.exists(os.path.join(d, '__init__.py')):
+            missing_dirs.add(d)
+
+    for d in sorted(missing_dirs):
+        print('No __init__.py file found in: {}'.format(d))
+
+    return 1 if len(missing_dirs) else 0
+
+
+if __name__ == '__main__':
+    exit(main())

setup.cfg

@@ -43,6 +43,7 @@ console_scripts =
     check-executables-have-shebangs = pre_commit_hooks.check_executables_have_shebangs:main
     check-json = pre_commit_hooks.check_json:main
     check-merge-conflict = pre_commit_hooks.check_merge_conflict:main
+    check-missing-inits = pre_commit_hooks.check_missing_inits:main
     check-symlinks = pre_commit_hooks.check_symlinks:main
     check-toml = pre_commit_hooks.check_toml:main
     check-vcs-permalinks = pre_commit_hooks.check_vcs_permalinks:main

tests/check_missing_inits_test.py

@@ -0,0 +1,62 @@
+import os
+
+import pytest
+
+from pre_commit_hooks.check_missing_inits import main
+
+
+@pytest.fixture
+def filepaths(tmpdir):
+    dirs = ['a', 'b']
+    files = ['a.py', 'b.py', '__init__.py']
+    paths = []
+    for d in dirs:
+        directory = tmpdir / d
+        os.mkdir(str(directory))
+        for f in files:
+            path = (directory / f)
+            paths.append(str(path))
+        # Nested directory
+        if d == 'b':
+            directory = directory / 'c'
+            os.mkdir(str(directory))
+            for f in files:
+                path = (directory / f)
+                paths.append(str(path))
+    return paths
+
+
+def test_has_inits(filepaths):
+    for f in filepaths:
+        with open(f, 'w'):
+            pass
+
+    assert main(argv=filepaths) == 0
+
+
+def test_missing_inits(filepaths):
+    remove = ''
+    for f in filepaths:
+        # Remove the init py file from the b directory
+        if os.path.join('b', '__init__.py') in f:
+            remove = str(f)
+            continue
+        with open(f, 'w'):
+            pass
+    filepaths.remove(remove)
+
+    assert main(argv=filepaths) == 1
+
+
+def test_nested_dirs_missing_inits(filepaths):
+    remove = ''
+    for f in filepaths:
+        # Remove the init py file from a nested directory
+        if os.path.join('b', 'c', '__init__.py') in f:
+            remove = str(f)
+            continue
+        with open(f, 'w'):
+            pass
+    filepaths.remove(remove)
+
+    assert main(argv=filepaths) == 1