forbid-new-submodules: fix triggering failure when only a submodule is committed (without any other file); support --from-ref and --to-ref; fixes #609

tests/forbid_new_submodules_test.py

@@ -1,22 +1,20 @@
+import os
 import subprocess
+from unittest import mock
 
 import pytest
 
 from pre_commit_hooks.forbid_new_submodules import main
+from testing.util import git_commit
 
 
 @pytest.fixture
 def git_dir_with_git_dir(tmpdir):
     with tmpdir.as_cwd():
         subprocess.check_call(('git', 'init', '.'))
-        subprocess.check_call((
-            'git', 'commit', '-m', 'init', '--allow-empty', '--no-gpg-sign',
-        ))
+        git_commit('--allow-empty', '-m', 'init')
         subprocess.check_call(('git', 'init', 'foo'))
-        subprocess.check_call(
-            ('git', 'commit', '-m', 'init', '--allow-empty', '--no-gpg-sign'),
-            cwd=str(tmpdir.join('foo')),
-        )
+        git_commit('--allow-empty', '-m', 'init', cwd=str(tmpdir.join('foo')))
         yield
 
 
@@ -31,7 +29,24 @@ def git_dir_with_git_dir(tmpdir):
 )
 def test_main_new_submodule(git_dir_with_git_dir, capsys, cmd):
     subprocess.check_call(cmd)
-    assert main() == 1
+    assert main(('random_non-related_file',)) == 0
+    assert main(('foo',)) == 1
+    out, _ = capsys.readouterr()
+    assert out.startswith('foo: new submodule introduced\n')
+
+
+def test_main_new_submodule_committed(git_dir_with_git_dir, capsys):
+    rev_parse_cmd = ('git', 'rev-parse', 'HEAD')
+    from_ref = subprocess.check_output(rev_parse_cmd).decode().strip()
+    subprocess.check_call(('git', 'submodule', 'add', './foo'))
+    git_commit('-m', 'new submodule')
+    to_ref = subprocess.check_output(rev_parse_cmd).decode().strip()
+    with mock.patch.dict(
+        os.environ,
+        {'PRE_COMMIT_FROM_REF': from_ref, 'PRE_COMMIT_TO_REF': to_ref},
+    ):
+        assert main(('random_non-related_file',)) == 0
+        assert main(('foo',)) == 1
     out, _ = capsys.readouterr()
     assert out.startswith('foo: new submodule introduced\n')
 
@@ -39,4 +54,4 @@ def test_main_new_submodule(git_dir_with_git_dir, capsys, cmd):
 def test_main_no_new_submodule(git_dir_with_git_dir):
     open('test.py', 'a+').close()
     subprocess.check_call(('git', 'add', 'test.py'))
-    assert main() == 0
+    assert main(('test.py',)) == 0