Add --write option to trigger running Transforms

Transforms, including read/write of YAML files, will be added in a follow-up PR.

src/ansiblelint/__main__.py

@@ -46,6 +46,7 @@
 if TYPE_CHECKING:
     # RulesCollection must be imported lazily or ansible gets imported too early.
     from ansiblelint.rules import RulesCollection
+    from ansiblelint.runner import LintResult
 
 
 _logger = logging.getLogger(__name__)
@@ -137,6 +138,19 @@ def _do_list(rules: "RulesCollection") -> int:
     return 1
 
 
+def _do_transform(result: "LintResult") -> None:
+    """Create and run Transformer."""
+    # On purpose lazy-imports to avoid loading transforms unless requested
+    # pylint: disable=import-outside-toplevel
+    from ansiblelint.transformer import Transformer
+
+    # future: maybe pass options to Transformer
+    transformer = Transformer(result)
+
+    # this will mark any matches as fixed if the transforms repaired the issue
+    transformer.run()
+
+
 def main(argv: Optional[List[str]] = None) -> int:
     """Linter CLI entry point."""
     # alter PATH if needed (venv support)
@@ -174,6 +188,9 @@ def main(argv: Optional[List[str]] = None) -> int:
 
     result = _get_matches(rules, options)
 
+    if options.write:
+        _do_transform(result)
+
     mark_as_success = False
     if result.matches and options.progressive:
         _logger.info(

src/ansiblelint/cli.py

@@ -189,6 +189,13 @@ def get_cli_parser() -> argparse.ArgumentParser:
         dest="use_default_rules",
         help="Keep default rules when using -r",
     )
+    parser.add_argument(
+        "--write",
+        dest="write",
+        action="store_true",
+        help="Reformat YAML files to standardize spacing, quotes, etc. "
+        "Future versions will expand this option so it fixes more issues.",
+    )
     parser.add_argument(
         "--show-relpath",
         dest="display_relative_path",

src/ansiblelint/config.py

@@ -69,6 +69,7 @@
     lintables=[],
     listrules=False,
     listtags=False,
+    write=False,
     parseable=False,
     quiet=False,
     rulesdirs=[],

src/ansiblelint/transformer.py

@@ -0,0 +1,28 @@
+"""Transformer implementation."""
+import logging
+from typing import List, Set
+
+from ansiblelint.errors import MatchError
+from ansiblelint.file_utils import Lintable
+from ansiblelint.runner import LintResult
+
+__all__ = ["Transformer"]
+
+_logger = logging.getLogger(__name__)
+
+
+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.
+    """
+
+    def __init__(self, result: LintResult):
+        """Initialize a Transformer instance."""
+        self.matches: List[MatchError] = result.matches
+        self.files: Set[Lintable] = result.files
+
+    def run(self) -> None:
+        """For each file, read it, execute transforms on it, then write it."""