change migrate-config to use yaml parse tree instead

pre_commit/yaml_rewrite.py

@@ -0,0 +1,52 @@
+from __future__ import annotations
+
+from collections.abc import Generator
+from collections.abc import Iterable
+from typing import NamedTuple
+from typing import Protocol
+
+from yaml.nodes import MappingNode
+from yaml.nodes import Node
+from yaml.nodes import ScalarNode
+from yaml.nodes import SequenceNode
+
+
+class _Matcher(Protocol):
+    def match(self, n: Node) -> Generator[Node]: ...
+
+
+class MappingKey(NamedTuple):
+    k: str
+
+    def match(self, n: Node) -> Generator[Node]:
+        if isinstance(n, MappingNode):
+            for k, _ in n.value:
+                if k.value == self.k:
+                    yield k
+
+
+class MappingValue(NamedTuple):
+    k: str
+
+    def match(self, n: Node) -> Generator[Node]:
+        if isinstance(n, MappingNode):
+            for k, v in n.value:
+                if k.value == self.k:
+                    yield v
+
+
+class SequenceItem(NamedTuple):
+    def match(self, n: Node) -> Generator[Node]:
+        if isinstance(n, SequenceNode):
+            yield from n.value
+
+
+def _match(gen: Iterable[Node], m: _Matcher) -> Iterable[Node]:
+    return (n for src in gen for n in m.match(src))
+
+
+def match(n: Node, matcher: tuple[_Matcher, ...]) -> Generator[ScalarNode]:
+    gen: Iterable[Node] = (n,)
+    for m in matcher:
+        gen = _match(gen, m)
+    return (n for n in gen if isinstance(n, ScalarNode))