1 files changed, 141 insertions, 0 deletions
diff --git a/src/ansiblelint/transformer.py b/src/ansiblelint/transformer.py
new file mode 100644
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+++ b/src/ansiblelint/transformer.py
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+"""Transformer implementation."""
+from __future__ import annotations
+
+import logging
+from argparse import Namespace
+from typing import Union, cast
+
+from ruamel.yaml.comments import CommentedMap, CommentedSeq
+
+from ansiblelint.errors import MatchError
+from ansiblelint.file_utils import Lintable
+from ansiblelint.rules import AnsibleLintRule, TransformMixin
+from ansiblelint.runner import LintResult
+from ansiblelint.yaml_utils import FormattedYAML, get_path_to_play, get_path_to_task
+
+__all__ = ["Transformer"]
+
+_logger = logging.getLogger(__name__)
+
+
+# pylint: disable=too-few-public-methods
+class Transformer:
+    """Transformer class marshals transformations.
+
+    The Transformer is similar to the ``ansiblelint.runner.Runner`` which manages
+    running each of the rules. We only expect there to be one ``Transformer`` instance
+    which should be instantiated from the main entrypoint function.
+
+    In the future, the transformer will be responsible for running transforms for each
+    of the rule matches. For now, it just reads/writes YAML files which is a
+    pre-requisite for the planned rule-specific transforms.
+    """
+
+    def __init__(self, result: LintResult, options: Namespace):
+        """Initialize a Transformer instance."""
+        self.write_set = self.effective_write_set(options.write_list)
+
+        self.matches: list[MatchError] = result.matches
+        self.files: set[Lintable] = result.files
+
+        lintables: dict[str, Lintable] = {file.filename: file for file in result.files}
+        self.matches_per_file: dict[Lintable, list[MatchError]] = {
+            file: [] for file in result.files
+        }
+
+        for match in self.matches:
+            try:
+                lintable = lintables[match.filename]
+            except KeyError:
+                # we shouldn't get here, but this is easy to recover from so do that.
+                lintable = Lintable(match.filename)
+                self.matches_per_file[lintable] = []
+            self.matches_per_file[lintable].append(match)
+
+    @staticmethod
+    def effective_write_set(write_list: list[str]) -> set[str]:
+        """Simplify write_list based on ``"none"`` and ``"all"`` keywords.
+
+        ``"none"`` resets the enabled rule transforms.
+        This returns ``{"none"}`` or a set of everything after the last ``"none"``.
+
+        If ``"all"`` is in the ``write_list`` (after ``"none"`` if present),
+        then this will return ``{"all"}``.
+        """
+        none_indexes = [i for i, value in enumerate(write_list) if value == "none"]
+        if none_indexes:
+            index = none_indexes[-1]
+            if len(write_list) > index + 1:
+                index += 1
+            write_list = write_list[index:]
+        if "all" in write_list:
+            return {"all"}
+        return set(write_list)
+
+    def run(self) -> None:
+        """For each file, read it, execute transforms on it, then write it."""
+        for file, matches in self.matches_per_file.items():
+            # str() convinces mypy that "text/yaml" is a valid Literal.
+            # Otherwise, it thinks base_kind is one of playbook, meta, tasks, ...
+            file_is_yaml = str(file.base_kind) == "text/yaml"
+
+            try:
+                data: str = file.content
+            except (UnicodeDecodeError, IsADirectoryError):
+                # we hit a binary file (eg a jar or tar.gz) or a directory
+                data = ""
+                file_is_yaml = False
+
+            ruamel_data: CommentedMap | CommentedSeq | None = None
+            if file_is_yaml:
+                # We need a fresh YAML() instance for each load because ruamel.yaml
+                # stores intermediate state during load which could affect loading
+                # any other files. (Based on suggestion from ruamel.yaml author)
+                yaml = FormattedYAML()
+
+                ruamel_data = yaml.loads(data)
+                if not isinstance(ruamel_data, (CommentedMap, CommentedSeq)):
+                    # This is an empty vars file or similar which loads as None.
+                    # It is not safe to write this file or data-loss is likely.
+                    # Only maps and sequences can preserve comments. Skip it.
+                    continue
+
+            if self.write_set != {"none"}:
+                self._do_transforms(file, ruamel_data or data, file_is_yaml, matches)
+
+            if file_is_yaml:
+                # noinspection PyUnboundLocalVariable
+                file.content = yaml.dumps(ruamel_data)
+
+            if file.updated:
+                file.write()
+
+    def _do_transforms(
+        self,
+        file: Lintable,
+        data: CommentedMap | CommentedSeq | str,
+        file_is_yaml: bool,
+        matches: list[MatchError],
+    ) -> None:
+        """Do Rule-Transforms handling any last-minute MatchError inspections."""
+        for match in sorted(matches):
+            if not isinstance(match.rule, TransformMixin):
+                continue
+            if self.write_set != {"all"}:
+                rule = cast(AnsibleLintRule, match.rule)
+                rule_definition = set(rule.tags)
+                rule_definition.add(rule.id)
+                if rule_definition.isdisjoint(self.write_set):
+                    # rule transform not requested. Skip it.
+                    continue
+            if file_is_yaml and not match.yaml_path:
+                data = cast(Union[CommentedMap, CommentedSeq], data)
+                if match.match_type == "play":
+                    match.yaml_path = get_path_to_play(file, match.linenumber, data)
+                elif match.task or file.kind in (
+                    "tasks",
+                    "handlers",
+                    "playbook",
+                ):
+                    match.yaml_path = get_path_to_task(file, match.linenumber, data)
+            match.rule.transform(match, file, data)