eagerly catch invalid yaml in migrate-config

pre_commit/commands/migrate_config.py

@@ -3,8 +3,10 @@ from __future__ import annotations
 import re
 import textwrap
 
+import cfgv
 import yaml
 
+from pre_commit.clientlib import InvalidConfigError
 from pre_commit.yaml import yaml_load
 
 
@@ -44,6 +46,13 @@ def migrate_config(config_file: str, quiet: bool = False) -> int:
     with open(config_file) as f:
         orig_contents = contents = f.read()
 
+    with cfgv.reraise_as(InvalidConfigError):
+        with cfgv.validate_context(f'File {config_file}'):
+            try:
+                yaml_load(orig_contents)
+            except Exception as e:
+                raise cfgv.ValidationError(str(e))
+
     contents = _migrate_map(contents)
     contents = _migrate_sha_to_rev(contents)
 

tests/commands/migrate_config_test.py

@@ -1,6 +1,9 @@
 from __future__ import annotations
 
+import pytest
+
 import pre_commit.constants as C
+from pre_commit.clientlib import InvalidConfigError
 from pre_commit.commands.migrate_config import migrate_config
 
 
@@ -129,3 +132,13 @@ def test_migrate_config_sha_to_rev(tmpdir):
         '    rev: v1.2.0\n'
         '    hooks: []\n'
     )
+
+
+def test_migrate_config_invalid_yaml(tmpdir):
+    contents = '['
+    cfg = tmpdir.join(C.CONFIG_FILE)
+    cfg.write(contents)
+    with tmpdir.as_cwd(), pytest.raises(InvalidConfigError) as excinfo:
+        migrate_config(C.CONFIG_FILE)
+    expected = '\n==> File .pre-commit-config.yaml\n=====> '
+    assert str(excinfo.value).startswith(expected)