Decouple pybabel frontend from distutils/setuptools; remove dependency

Fixes #1040

.pre-commit-config.yaml

@@ -19,6 +19,6 @@ repos:
         exclude: (tests/messages/data/)
       - id: name-tests-test
         args: [ '--django' ]
-        exclude: (tests/messages/data/)
+        exclude: (tests/messages/data/|.*(consts|utils).py)
       - id: requirements-txt-fixer
       - id: trailing-whitespace

babel/messages/frontend.py

@@ -40,22 +40,17 @@
 
 log = logging.getLogger('babel')
 
-try:
-    # See: https://setuptools.pypa.io/en/latest/deprecated/distutils-legacy.html
-    from setuptools import Command as _Command
-    distutils_log = log  # "distutils.log → (no replacement yet)"
 
-    try:
-        from setuptools.errors import BaseError, OptionError, SetupError
-    except ImportError:  # Error aliases only added in setuptools 59 (2021-11).
-        OptionError = SetupError = BaseError = Exception
+class BaseError(Exception):
+    pass
 
-except ImportError:
-    from distutils import log as distutils_log
-    from distutils.cmd import Command as _Command
-    from distutils.errors import DistutilsError as BaseError
-    from distutils.errors import DistutilsOptionError as OptionError
-    from distutils.errors import DistutilsSetupError as SetupError
+
+class OptionError(BaseError):
+    pass
+
+
+class SetupError(BaseError):
+    pass
 
 
 def listify_value(arg, split=None):
@@ -100,7 +95,7 @@ def listify_value(arg, split=None):
     return out
 
 
-class Command(_Command):
+class CommandMixin:
     # This class is a small shim between Distutils commands and
     # optparse option parsing in the frontend command line.
 
@@ -128,7 +123,7 @@ class Command(_Command):
     option_choices = {}
 
     #: Log object. To allow replacement in the script command line runner.
-    log = distutils_log
+    log = log
 
     def __init__(self, dist=None):
         # A less strict version of distutils' `__init__`.
@@ -140,24 +135,21 @@ def __init__(self, dist=None):
         self.help = 0
         self.finalized = 0
 
+    def initialize_options(self):
+        pass
 
-class compile_catalog(Command):
-    """Catalog compilation command for use in ``setup.py`` scripts.
-
-    If correctly installed, this command is available to Setuptools-using
-    setup scripts automatically. For projects using plain old ``distutils``,
-    the command needs to be registered explicitly in ``setup.py``::
-
-        from babel.messages.frontend import compile_catalog
+    def ensure_finalized(self):
+        if not self.finalized:
+            self.finalize_options()
+        self.finalized = 1
 
-        setup(
-            ...
-            cmdclass = {'compile_catalog': compile_catalog}
+    def finalize_options(self):
+        raise RuntimeError(
+            f"abstract method -- subclass {self.__class__} must override",
         )
 
-    .. versionadded:: 0.9
-    """
 
+class CompileCatalog(CommandMixin):
     description = 'compile message catalogs to binary MO files'
     user_options = [
         ('domain=', 'D',
@@ -280,31 +272,19 @@ def _make_directory_filter(ignore_patterns):
     """
     Build a directory_filter function based on a list of ignore patterns.
     """
+
     def cli_directory_filter(dirname):
         basename = os.path.basename(dirname)
         return not any(
             fnmatch.fnmatch(basename, ignore_pattern)
             for ignore_pattern
             in ignore_patterns
         )
-    return cli_directory_filter
-
-
-class extract_messages(Command):
-    """Message extraction command for use in ``setup.py`` scripts.
 
-    If correctly installed, this command is available to Setuptools-using
-    setup scripts automatically. For projects using plain old ``distutils``,
-    the command needs to be registered explicitly in ``setup.py``::
+    return cli_directory_filter
 
-        from babel.messages.frontend import extract_messages
-
-        setup(
-            ...
-            cmdclass = {'extract_messages': extract_messages}
-        )
-    """
 
+class ExtractMessages(CommandMixin):
     description = 'extract localizable strings from the project code'
     user_options = [
         ('charset=', None,
@@ -497,6 +477,7 @@ def callback(filename: str, method: str, options: dict):
                 opt_values = ", ".join(f'{k}="{v}"' for k, v in options.items())
                 optstr = f" ({opt_values})"
             self.log.info('extracting messages from %s%s', filepath, optstr)
+
         return callback
 
     def run(self):
@@ -572,38 +553,7 @@ def _get_mappings(self):
         return mappings
 
 
-def check_message_extractors(dist, name, value):
-    """Validate the ``message_extractors`` keyword argument to ``setup()``.
-
-    :param dist: the distutils/setuptools ``Distribution`` object
-    :param name: the name of the keyword argument (should always be
-                 "message_extractors")
-    :param value: the value of the keyword argument
-    :raise `DistutilsSetupError`: if the value is not valid
-    """
-    assert name == 'message_extractors'
-    if not isinstance(value, dict):
-        raise SetupError(
-            'the value of the "message_extractors" '
-            'parameter must be a dictionary'
-        )
-
-
-class init_catalog(Command):
-    """New catalog initialization command for use in ``setup.py`` scripts.
-
-    If correctly installed, this command is available to Setuptools-using
-    setup scripts automatically. For projects using plain old ``distutils``,
-    the command needs to be registered explicitly in ``setup.py``::
-
-        from babel.messages.frontend import init_catalog
-
-        setup(
-            ...
-            cmdclass = {'init_catalog': init_catalog}
-        )
-    """
-
+class InitCatalog(CommandMixin):
     description = 'create a new catalog based on a POT file'
     user_options = [
         ('domain=', 'D',
@@ -678,23 +628,7 @@ def run(self):
             write_po(outfile, catalog, width=self.width)
 
 
-class update_catalog(Command):
-    """Catalog merging command for use in ``setup.py`` scripts.
-
-    If correctly installed, this command is available to Setuptools-using
-    setup scripts automatically. For projects using plain old ``distutils``,
-    the command needs to be registered explicitly in ``setup.py``::
-
-        from babel.messages.frontend import update_catalog
-
-        setup(
-            ...
-            cmdclass = {'update_catalog': update_catalog}
-        )
-
-    .. versionadded:: 0.9
-    """
-
+class UpdateCatalog(CommandMixin):
     description = 'update message catalogs from a POT file'
     user_options = [
         ('domain=', 'D',
@@ -911,10 +845,10 @@ class CommandLineInterface:
     }
 
     command_classes = {
-        'compile': compile_catalog,
-        'extract': extract_messages,
-        'init': init_catalog,
-        'update': update_catalog,
+        'compile': CompileCatalog,
+        'extract': ExtractMessages,
+        'init': InitCatalog,
+        'update': UpdateCatalog,
     }
 
     log = None  # Replaced on instance level
@@ -996,7 +930,7 @@ def _configure_command(self, cmdname, argv):
         cmdinst = cmdclass()
         if self.log:
             cmdinst.log = self.log  # Use our logger, not distutils'.
-        assert isinstance(cmdinst, Command)
+        assert isinstance(cmdinst, CommandMixin)
         cmdinst.initialize_options()
 
         parser = optparse.OptionParser(
@@ -1113,7 +1047,8 @@ def parse_mapping(fileobj, filename=None):
 
     return method_map, options_map
 
-def _parse_spec(s: str) -> tuple[int | None, tuple[int|tuple[int, str], ...]]:
+
+def _parse_spec(s: str) -> tuple[int | None, tuple[int | tuple[int, str], ...]]:
     inds = []
     number = None
     for x in s.split(','):
@@ -1125,6 +1060,7 @@ def _parse_spec(s: str) -> tuple[int | None, tuple[int|tuple[int, str], ...]]:
             inds.append(int(x))
     return number, tuple(inds)
 
+
 def parse_keywords(strings: Iterable[str] = ()):
     """Parse keywords specifications from the given list of strings.
 
@@ -1173,5 +1109,19 @@ def parse_keywords(strings: Iterable[str] = ()):
     return keywords
 
 
+try:
+    # Re-exports for backwards compatibility;
+    # `setuptools_frontend` is the canonical import location.
+    from babel.messages.setuptools_frontend import (
+        check_message_extractors,  # noqa: F401
+        compile_catalog,  # noqa: F401
+        extract_messages,  # noqa: F401
+        init_catalog,  # noqa: F401
+        update_catalog,  # noqa: F401
+    )
+except ImportError:
+    # We expect this to mean that neither setuptools or distutils are installed.
+    pass
+
 if __name__ == '__main__':
     main()

babel/messages/setuptools_frontend.py

@@ -0,0 +1,108 @@
+from __future__ import annotations
+
+from babel.messages import frontend
+
+try:
+    # See: https://setuptools.pypa.io/en/latest/deprecated/distutils-legacy.html
+    from setuptools import Command
+
+    try:
+        from setuptools.errors import BaseError, OptionError, SetupError
+    except ImportError:  # Error aliases only added in setuptools 59 (2021-11).
+        OptionError = SetupError = BaseError = Exception
+
+except ImportError:
+    from distutils.cmd import Command
+    from distutils.errors import DistutilsSetupError as SetupError
+
+
+def check_message_extractors(dist, name, value):
+    """Validate the ``message_extractors`` keyword argument to ``setup()``.
+
+    :param dist: the distutils/setuptools ``Distribution`` object
+    :param name: the name of the keyword argument (should always be
+                 "message_extractors")
+    :param value: the value of the keyword argument
+    :raise `DistutilsSetupError`: if the value is not valid
+    """
+    assert name == "message_extractors"
+    if not isinstance(value, dict):
+        raise SetupError(
+            'the value of the "message_extractors" parameter must be a dictionary'
+        )
+
+
+class compile_catalog(frontend.CompileCatalog, Command):
+    """Catalog compilation command for use in ``setup.py`` scripts.
+
+    If correctly installed, this command is available to Setuptools-using
+    setup scripts automatically. For projects using plain old ``distutils``,
+    the command needs to be registered explicitly in ``setup.py``::
+
+        from babel.messages.setuptools_frontend import compile_catalog
+
+        setup(
+            ...
+            cmdclass = {'compile_catalog': compile_catalog}
+        )
+
+    .. versionadded:: 0.9
+    """
+
+
+class extract_messages(frontend.ExtractMessages, Command):
+    """Message extraction command for use in ``setup.py`` scripts.
+
+    If correctly installed, this command is available to Setuptools-using
+    setup scripts automatically. For projects using plain old ``distutils``,
+    the command needs to be registered explicitly in ``setup.py``::
+
+        from babel.messages.setuptools_frontend import extract_messages
+
+        setup(
+            ...
+            cmdclass = {'extract_messages': extract_messages}
+        )
+    """
+
+
+class init_catalog(frontend.InitCatalog, Command):
+    """New catalog initialization command for use in ``setup.py`` scripts.
+
+    If correctly installed, this command is available to Setuptools-using
+    setup scripts automatically. For projects using plain old ``distutils``,
+    the command needs to be registered explicitly in ``setup.py``::
+
+        from babel.messages.setuptools_frontend import init_catalog
+
+        setup(
+            ...
+            cmdclass = {'init_catalog': init_catalog}
+        )
+    """
+
+
+class update_catalog(frontend.UpdateCatalog, Command):
+    """Catalog merging command for use in ``setup.py`` scripts.
+
+    If correctly installed, this command is available to Setuptools-using
+    setup scripts automatically. For projects using plain old ``distutils``,
+    the command needs to be registered explicitly in ``setup.py``::
+
+        from babel.messages.setuptools_frontend import update_catalog
+
+        setup(
+            ...
+            cmdclass = {'update_catalog': update_catalog}
+        )
+
+    .. versionadded:: 0.9
+    """
+
+
+COMMANDS = {
+    "compile_catalog": compile_catalog,
+    "extract_messages": extract_messages,
+    "init_catalog": init_catalog,
+    "update_catalog": update_catalog,
+}

conftest.py

@@ -2,7 +2,11 @@
 
 from _pytest.doctest import DoctestModule
 
-collect_ignore = ['tests/messages/data', 'setup.py']
+collect_ignore = [
+    'babel/messages/setuptools_frontend.py',
+    'setup.py',
+    'tests/messages/data',
+]
 babel_path = Path(__file__).parent / 'babel'