Pyupgrade formatter plugin

.github/workflows/pylint.yml

@@ -22,7 +22,9 @@ jobs:
             defusedxml \
             pygments \
             'pylint<=3.2.7' \
+            pylint-per-file-ignores \
             pytest>=6.2.0 \
+            pyupgrade>=2.31.0 \
             regex \
             requests \
             requests-cache \

.github/workflows/pyupgrade.yml

@@ -9,16 +9,13 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
       - name: Install uv
         uses: astral-sh/setup-uv@v3
       - uses: actions/setup-python@v5
       - name: Ensure modern Python style using pyupgrade
-        # This script is written in a Linux / macos / windows portable way
         run: |
-          uvx --from pyupgrade python -c "
-          import sys
-          from pyupgrade._main import main
-          from glob import glob
-          files = glob('**/*.py', recursive=True)
-          sys.exit(main(files + ['--py39-plus']))
-          " || ( git diff ; false )
+          uvx \
+            --from '.[pyupgrade]' \
+            darker --formatter=pyupgrade --target-version=py39 --diff

.github/workflows/test-working-directory.yml

@@ -1,6 +1,11 @@
 ---
 name: "GH Action `working-directory:` test"
 
+# If these tests fail with "fatal: bad object" in the "Run Darker" step
+# and "Error: Expected exit code <n>" in the "Check exit code" step,
+# make sure `fetch-steps:` in `actions/checkout` below is
+# at least as large as the number of commits in the branch the test is run in.
+
 on: push  # yamllint disable-line rule:truthy
 
 jobs:
@@ -66,7 +71,9 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          fetch-depth: 10
+          # This needs to be at least the number of commits
+          # in the branch the test is run in:
+          fetch-depth: 30
 
       - name: Download test repository
         uses: actions/download-artifact@v3

CHANGES.rst

@@ -10,8 +10,8 @@ Added
 - Display exit code in parentheses after error message.
 - Do not reformat renamed files.
 - CI workflow to post recent project activity in a discussion. Triggered manually.
-- CI "future" test now tests against ``main`` of Darkgraylib_ in addition to Black_,
-  Flynt_ and isort_.
+- CI "future" test now tests against ``main`` of Darkgraylib_ and pyupgrade_ in addition
+  to Black_, Flynt_ and isort_.
 - The ``--preview`` configuration flag is now supported in the configuration files for
   Darker and Black
 - Prevent Pylint from updating beyond version 3.2.7 due to dropped Python 3.8 support.
@@ -23,6 +23,8 @@ Added
   Isort or Flynt_.
 - Black_ is no longer installed by default. Use ``pip install 'darker[black]'`` to get
   Black support.
+- pyupgrade_ is now supported as a formatter plugin. Note that changes from pyupgrade
+  are applied on a per-file basis, not only for modified lines as with Black_ and Ruff_.
 
 Removed
 -------
@@ -697,3 +699,4 @@ Added
 .. _Black: https://black.readthedocs.io/
 .. _isort: https://pycqa.github.io/isort/
 .. _NixOS: https://nixos.org/
+.. _pyupgrade: https://pypi.org/project/pyupgrade/

README.rst

@@ -378,7 +378,8 @@ The following `command line arguments`_ can also be used to modify the defaults:
        versions that should be supported by Black's output. [default: per-file auto-
        detection]
 --formatter FORMATTER
-       [black\|none\|ruff] Formatter to use for reformatting code. [default: black]
+       [black\|none\|pyupgrade\|ruff] Formatter to use for reformatting code. [default:
+       black]
 
 To change default values for these options for a given project,
 add a ``[tool.darker]`` section to ``pyproject.toml`` in the project's root directory,

constraints-future.txt

@@ -7,3 +7,4 @@ black @ git+https://github.com/psf/black.git@main
 darkgraylib @ git+https://github.com/akaihola/darkgraylib.git@main
 flynt @ git+https://github.com/ikamensh/flynt.git@master
 isort @ git+https://github.com/PyCQA/isort.git@main
+pyupgrade @ git+https://github.com/asottile/pyupgrade.git@main

mypy.ini

@@ -1,4 +1,6 @@
 [mypy]
+mypy_path = stubs/
+
 disallow_any_unimported = True
 disallow_any_expr = False
 disallow_any_decorated = True

pyproject.toml

@@ -31,10 +31,18 @@ revision = "origin/master..."
 revision = "origin/master..."
 src = ["."]
 
+[tool.pylint.MASTER]
+load-plugins = [
+    "pylint_per_file_ignores",
+]
+
 [tool.pylint."messages control"]
 # Check import order only with isort. Pylint doesn't support a custom list of first
 # party packages. We want to consider "darkgraylib" and "graylint" as first party.
 disable = ["wrong-import-order"]
+per-file-ignores = [
+  "/stubs/:missing-class-docstring,missing-function-docstring,unused-argument",
+]
 
 [tool.ruff]
 target-version = "py39"
@@ -47,6 +55,7 @@ ignore = [
     "D203",  # One blank line required before class docstring
     "D213",  # Multi-line docstring summary should start at the second line
     "D400",  # First line should end with a period (duplicates D415)
+    "ISC001",  # Checks for implicitly concatenated strings on a single line
 ]
 
 [tool.ruff.lint.per-file-ignores]

setup.cfg

@@ -46,6 +46,7 @@ darker =
 darker.formatter =
     black = darker.formatters.black_formatter:BlackFormatter
     ruff = darker.formatters.ruff_formatter:RuffFormatter
+    pyupgrade = darker.formatters.pyupgrade_formatter:PyupgradeFormatter
     none = darker.formatters.none_formatter:NoneFormatter
 console_scripts =
     darker = darker.__main__:main_with_error_handling
@@ -59,6 +60,8 @@ isort =
     isort>=5.0.1
 color =
     Pygments>=2.4.0
+pyupgrade =
+    pyupgrade>=2.31.0
 test =
     # NOTE: remember to keep `constraints-oldest.txt` in sync with these
     black>=22.3.0
@@ -72,8 +75,10 @@ test =
     pydocstyle
     pygments
     pylint<=3.2.7  # pylint 3.3.0 dropped Python 3.8 support
+    pylint-per-file-ignores
     pytest>=6.2.0
     pytest-kwparametrize>=0.0.3
+    pyupgrade>=2.31.0
     regex>=2021.4.4
     requests_cache>=0.7
     ruamel.yaml>=0.17.21

src/darker/__main__.py

@@ -227,9 +227,17 @@ def _reformat_and_flynt_single_file(  # noqa: PLR0913
         "no" if formatted == fstringified else "some",
         len(formatted.lines),
     )
+    # 4. apply all re-formatter modifications if the re-formatter doesn't guarantee
+    #    preserving the abstract syntax tree (AST); otherwise do steps 5 to 10
+    if not formatter.preserves_ast:
+        logger.debug(
+            "Preserving the AST not guaranteed by %s, applying all changes",
+            formatter.name,
+        )
+        return formatted
 
-    # 4. get a diff between the edited to-file and the processed content
-    # 5. convert the diff into chunks, keeping original and reformatted content for each
+    # 5. get a diff between the edited to-file and the processed content
+    # 6. convert the diff into chunks, keeping original and reformatted content for each
     #    chunk
     new_chunks = diff_chunks(rev2_isorted, formatted)
 
@@ -337,9 +345,9 @@ def _drop_changes_on_unedited_lines(
                 context_lines,
                 abspath_in_rev2,
             )
-        # 6. diff the given revisions (optionally with isort modifications) for each
+        # 7. diff the given revisions (optionally with isort modifications) for each
         #    file
-        # 7. extract line numbers in each edited to-file for changed lines
+        # 8. extract line numbers in each edited to-file for changed lines
         edited_linenums = edited_linenums_differ.revision_vs_lines(
             relpath_in_repo, rev2_isorted, context_lines
         )
@@ -348,7 +356,7 @@ def _drop_changes_on_unedited_lines(
             last_successful_reformat = rev2_isorted
             break
 
-        # 8. choose processed content for each chunk if there were any changed lines
+        # 9. choose processed content for each chunk if there were any changed lines
         #    inside the chunk in the edited to-file, or choose the chunk's original
         #    contents if no edits were done in that chunk
         chosen = TextDocument.from_lines(
@@ -358,8 +366,8 @@ def _drop_changes_on_unedited_lines(
             mtime=datetime.utcnow().strftime(GIT_DATEFORMAT),
         )
 
-        # 9. verify that the resulting reformatted source code parses to an identical
-        #    AST as the original edited to-file
+        # 10. verify that the resulting reformatted source code parses to an identical
+        #     AST as the original edited to-file
         if not has_fstring_changes and not verifier.is_equivalent_to_baseline(chosen):
             logger.debug(
                 "Verifying that the %s original edited lines and %s reformatted lines "
@@ -459,32 +467,26 @@ def _import_pygments():  # type: ignore
 def main(  # noqa: C901,PLR0912,PLR0915
     argv: List[str] = None,
 ) -> int:
-    """Parse the command line and reformat and optionally lint each source file
+    """Parse the command line and reformat and optionally lint each source file.
 
     1. run isort on each edited file (optional)
     2. run flynt (optional) on the isorted contents of each edited to-file
     3. run a code re-formatter on the isorted and fstringified contents of each edited
        to-file
-    4. get a diff between the edited to-file and the processed content
-    5. convert the diff into chunks, keeping original and reformatted content for each
+    4. apply all re-formatter modifications if the re-formatter doesn't guarantee
+       preserving the abstract syntax tree (AST); otherwise do steps 5 to 10
+    5. get a diff between the edited to-file and the processed content
+    6. convert the diff into chunks, keeping original and reformatted content for each
        chunk
-    6. diff the given revisions (optionally with isort modifications) for each
+    7. diff the given revisions (optionally with isort modifications) for each
        file
-    7. extract line numbers in each edited to-file for changed lines
-    8. choose processed content for each chunk if there were any changed lines inside
+    8. extract line numbers in each edited to-file for changed lines
+    9. choose processed content for each chunk if there were any changed lines inside
        the chunk in the edited to-file, or choose the chunk's original contents if no
        edits were done in that chunk
-    9. verify that the resulting reformatted source code parses to an identical AST as
-       the original edited to-file
-    9. write the reformatted source back to the original file or print the diff
-    10. run linter subprocesses twice for all modified and unmodified files which are
-        mentioned on the command line: first establish a baseline by running against
-        ``rev1``, then get current linting status by running against the working tree
-        (steps 10.-12. are optional)
-    11. create a mapping from line numbers of unmodified lines in the current versions
-        to corresponding line numbers in ``rev1``
-    12. hide linter messages which appear in the current versions and identically on
-        corresponding lines in ``rev1``, and show all other linter messages
+    10. verify that the resulting reformatted source code parses to an identical AST as
+        the original edited to-file
+    11. write the reformatted source back to the original file or print the diff
 
     :param argv: The command line arguments to the ``darker`` command
     :return: 1 if the ``--check`` argument was provided and at least one file was (or
@@ -611,7 +613,7 @@ def main(  # noqa: C901,PLR0912,PLR0915
             workers=config["workers"],
         ),
     ):
-        # 10. A re-formatted Python file which produces an identical AST was
+        # 11. A re-formatted Python file which produces an identical AST was
         #     created successfully - write an updated file or print the diff if
         #     there were any changes to the original
         formatting_failures_on_modified_lines = True

src/darker/formatters/base_formatter.py

@@ -29,6 +29,7 @@ class BaseFormatter(HasConfig[FormatterConfig]):
     """Base class for code re-formatters."""
 
     name: str
+    preserves_ast: bool
 
     def read_config(self, src: tuple[str, ...], args: Namespace) -> None:
         """Read code re-formatter configuration from a configuration file.

src/darker/formatters/black_formatter.py

@@ -79,6 +79,7 @@ class BlackFormatter(BaseFormatter, HasConfig[BlackCompatibleConfig]):
 
     name = "black"
     config_section = "tool.black"
+    preserves_ast = True
 
     def read_config(self, src: tuple[str, ...], args: Namespace) -> None:
         """Read Black configuration from ``pyproject.toml``.

src/darker/formatters/none_formatter.py

@@ -17,6 +17,7 @@ class NoneFormatter(BaseFormatter):
     """A dummy code formatter plugin interface."""
 
     name = "dummy reformat"
+    preserves_ast = True
 
     def run(
         self, content: TextDocument, path_from_cwd: Path  # noqa: ARG002

src/darker/formatters/pyupgrade_config.py

@@ -0,0 +1,11 @@
+"""Pyupgrade code formatter plugin configuration type definitions."""
+
+from __future__ import annotations
+
+from darker.formatters.formatter_config import FormatterConfig
+
+
+class PyupgradeConfig(FormatterConfig, total=False):
+    """Type definition for configuration dictionaries of Black compatible formatters."""
+
+    target_version: tuple[int, int]