Move pyupgrade tooling to a dedicated module

mypy.ini

@@ -87,6 +87,9 @@ ignore_missing_imports = True
 [mypy-pytest.*]
 ignore_missing_imports = True
 
+[mypy-pyupgrade.*]
+ignore_missing_imports = True
+
 [mypy-setuptools.*]
 ignore_missing_imports = True
 

src/darker/__main__.py

@@ -260,24 +260,6 @@ def _blacken_single_file( # pylint: disable=too-many-arguments,too-many-locals
  return last_successful_reformat
 
 
-def pyup(content: TextDocument) -> TextDocument:
- """Upgrade syntax to newer version of Python using `pyupgrade`
-
- :param content: The Python source code to upgrade
- :return: The upgraded Python source code
-
- """
-
- from pyupgrade._main import _fix_plugins, _fix_tokens, _fix_py36_plus, Settings
-
- min_version = (3, 6)
- result = _fix_plugins(content.string, Settings(min_version=min_version))
- result = _fix_tokens(result, min_version)
- result = _fix_py36_plus(result, min_version=min_version)
-
- return TextDocument(result)
-
-
 def modify_file(path: Path, new_content: TextDocument) -> None:
  """Write new content to a file and inform the user by logging"""
  logger.info("Writing %s bytes into %s", len(new_content.string), path)

src/darker/syntax_upgrade.py

@@ -0,0 +1,29 @@
+"""Wrapper for applying `pyupgrade` on Python source code"""
+
+from darker.utils import TextDocument
+
+try:
+ from pyupgrade import _main as pyupgrade_main
+except ImportError:
+ # `pyupgrade` is an optional dependency. Prevent the `ImportError` if it's missing.
+ pyupgrade_main = None
+
+
+__all__ = ["apply_pyupgrade", "pyupgrade_main"]
+
+
+def apply_pyupgrade(content: TextDocument) -> TextDocument:
+ """Upgrade syntax to newer version of Python using `pyupgrade`
+
+ :param content: The Python source code to upgrade
+ :return: The upgraded Python source code
+
+ """
+ # pylint: disable=protected-access
+ min_version = (3, 6)
+ result = pyupgrade_main._fix_plugins(
+ content.string, pyupgrade_main.Settings(min_version=min_version)
+ )
+ result = pyupgrade_main._fix_tokens(result, min_version)
+ result = pyupgrade_main._fix_py36_plus(result, min_version=min_version)
+ return TextDocument.from_str(result)