Add pre-commit hook

Check the migrations files in the current repository and
ensure that they all have a `safe` property defined.
While we can think of easy ways to break this implementation,
for all the use-cases I've had this covers it quite nicely
so I think it's worth merging even if its rough.

Tim Schilling put an initial sketch of this in
#39
and I was able to modify it for use in a precommit hook
without difficulty. The modifications were made to tailor
it to the environment of pre-commit, where file names are
passed to the command as arguments. This allows pre-commit
to only need to run the checks incrementally for the affected
files for new commits.

Co-authored-by: Tim Schilling <schillingt@better-simple.com>

.pre-commit-hooks.yaml

@@ -0,0 +1,9 @@
+-   id: check
+    name: Check migrations safety
+    description: Ensure that all local migrations have been marked for safety.
+    entry: safemigrate-check
+    language: python
+    files: migrations/\d{4}_.+\.py$
+    types: [file, python, text]
+    stages: [pre-commit, pre-merge-commit, pre-push, manual]
+    pass_filenames: true

pyproject.toml

@@ -33,3 +33,6 @@ django = ">=3.2,<5.0"
 
 [tool.poetry.dev-dependencies]
 tox = "*"
+
+[tool.poetry.plugins."console_scripts"]
+"safemigrate-check" = "django_safemigrate.check:main"

src/django_safemigrate/check.py

@@ -0,0 +1,56 @@
+"""
+Ensure migrations are using django_safemigrate.
+
+This is fairly rudimentary and won't work if the class doesn't
+explicitly inherit from ``Migration``.
+"""
+import re
+import sys
+
+MIGRATION_PATTERN = re.compile(r"class\s+(?P<MigrationClass>\w+)\s?\(.*Migration\):")
+
+MISSING_SAFE_MESSAGE = (
+    "{file_path}: {migration_class} is missing the 'safe' attribute.\n"
+)
+FAILURE_MESSAGE = (
+    "\n"
+    "Add the following to the migration class:\n"
+    "\n"
+    "from django_safemigrate import Safe\n"
+    "class Migration(migrations.Migration):\n"
+    "    safe = Safe.before_deploy\n"
+    "\n"
+    "You can also use the following:\n"
+    "    safe = Safe.always\n"
+    "    safe = Safe.after_deploy\n"
+    "\n"
+)
+
+
+def validate_migrations(files):
+    success = True
+    for file_path in files:
+        with open(file_path) as f:
+            content = f.read()
+
+        match = MIGRATION_PATTERN.search(content)
+        if match:
+            migration_class = match.group("MigrationClass")
+            if "safe = Safe." not in content:
+                success = False
+                sys.stdout.write(
+                    MISSING_SAFE_MESSAGE.format(
+                        file_path=file_path, migration_class=migration_class
+                    )
+                )
+    if not success:
+        sys.stdout.write(FAILURE_MESSAGE)
+    return success
+
+
+def main():  # pragma: no cover
+    sys.exit(0 if validate_migrations(sys.argv[1:]) else 1)
+
+
+if __name__ == "__main__":  # pragma: no cover
+    main()

tests/safemigrate_test.py

@@ -3,6 +3,7 @@
 from django.core.management.base import CommandError
 
 from django_safemigrate import Safe
+from django_safemigrate.check import validate_migrations
 from django_safemigrate.management.commands.safemigrate import Command
 
 
@@ -265,3 +266,37 @@ def test_boolean_invalid(self, receiver):
         plan = [(Migration("spam", "0001_initial", safe=False), False)]
         with pytest.raises(CommandError):
             receiver(plan=plan)
+
+
+class TestCheck:
+    """Exercise the check command."""
+
+    MARKED = """
+from django.db import migrations
+from django_safemigrate import Safe
+
+class Migration(migrations.Migration):
+    safe = Safe.always
+"""
+
+    UNMARKED = """
+from django.db import migrations
+
+class Migration(migrations.Migration):
+    pass
+"""
+
+    def test_validate_migrations_success(self, tmp_path):
+        with open(tmp_path / "0001_initial.py", "w") as f:
+            f.write(self.MARKED)
+        assert validate_migrations([tmp_path / "0001_initial.py"])
+
+    def test_validate_migrations_failure(self, tmp_path):
+        with open(tmp_path / "0001_initial.py", "w") as f:
+            f.write(self.UNMARKED)
+        assert not validate_migrations([tmp_path / "0001_initial.py"])
+
+    def test_validate_migrations_falsematch(self, tmp_path):
+        with open(tmp_path / "0001_initial.py", "w") as f:
+            f.write("THIS IS NOT A MIGRATION")
+        assert validate_migrations([tmp_path / "0001_initial.py"])