migrate-config rewrites deprecated stages

pre_commit/commands/migrate_config.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import functools
+import itertools
 import textwrap
 from typing import Callable
 
@@ -49,6 +50,10 @@ def _preserve_style(n: ScalarNode, *, s: str) -> str:
     return f'{n.style}{s}{n.style}'
 
 
+def _fix_stage(n: ScalarNode) -> str:
+    return _preserve_style(n, s=f'pre-{n.value}')
+
+
 def _migrate_composed(contents: str) -> str:
     tree = yaml_compose(contents)
     rewrites: list[tuple[ScalarNode, Callable[[ScalarNode], str]]] = []
@@ -76,6 +81,22 @@ def _migrate_composed(contents: str) -> str:
         if node.value == 'python_venv':
             rewrites.append((node, python_venv_replace))
 
+    # stages rewrites
+    default_stages_matcher = (MappingValue('default_stages'), SequenceItem())
+    default_stages_match = match(tree, default_stages_matcher)
+    hook_stages_matcher = (
+        MappingValue('repos'),
+        SequenceItem(),
+        MappingValue('hooks'),
+        SequenceItem(),
+        MappingValue('stages'),
+        SequenceItem(),
+    )
+    hook_stages_match = match(tree, hook_stages_matcher)
+    for node in itertools.chain(default_stages_match, hook_stages_match):
+        if node.value in {'commit', 'push', 'merge-commit'}:
+            rewrites.append((node, _fix_stage))
+
     rewrites.sort(reverse=True, key=lambda nf: nf[0].start_mark.index)
 
     src_parts = []