Add initial support for license expression (PEP 639)

docs/userguide/pyproject_config.rst

@@ -49,7 +49,7 @@ The ``project`` table contains metadata fields as described by the
    readme = "README.rst"
    requires-python = ">=3.8"
    keywords = ["one", "two"]
-   license = {text = "BSD-3-Clause"}
+   license = "BSD-3-Clause"
    classifiers = [
        "Framework :: Django",
        "Programming Language :: Python :: 3",

newsfragments/4706.feature.rst

@@ -0,0 +1 @@
+Added initial support for license expression (`PEP 639 <https://peps.python.org/pep-0639/#add-license-expression-field>`_). -- by :user:`cdce8p`

setuptools/_core_metadata.py

@@ -88,6 +88,7 @@ def read_pkg_file(self, file):
     self.url = _read_field_from_msg(msg, 'home-page')
     self.download_url = _read_field_from_msg(msg, 'download-url')
     self.license = _read_field_unescaped_from_msg(msg, 'license')
+    self.license_expression = _read_field_unescaped_from_msg(msg, 'license-expression')
 
     self.long_description = _read_field_unescaped_from_msg(msg, 'description')
     if self.long_description is None and self.metadata_version >= Version('2.1'):
@@ -175,7 +176,7 @@ def write_field(key, value):
         if attr_val is not None:
             write_field(field, attr_val)
 
-    license = self.get_license()
+    license = self.license_expression or self.get_license()
     if license:
         write_field('License', rfc822_escape(license))
 

setuptools/config/_apply_pyprojecttoml.py

@@ -58,6 +58,7 @@ def apply(dist: Distribution, config: dict, filename: StrPath) -> Distribution:
     os.chdir(root_dir)
     try:
         dist._finalize_requires()
+        dist._finalize_license_expression()
         dist._finalize_license_files()
     finally:
         os.chdir(current_directory)
@@ -181,16 +182,19 @@ def _long_description(
         dist._referenced_files.add(file)
 
 
-def _license(dist: Distribution, val: dict, root_dir: StrPath | None):
+def _license(dist: Distribution, val: str | dict, root_dir: StrPath | None):
     from setuptools.config import expand
 
-    if "file" in val:
-        # XXX: Is it completely safe to assume static?
-        value = expand.read_files([val["file"]], root_dir)
-        _set_config(dist, "license", _static.Str(value))
-        dist._referenced_files.add(val["file"])
+    if isinstance(val, str):
+        _set_config(dist, "license_expression", _static.Str(val))
     else:
-        _set_config(dist, "license", _static.Str(val["text"]))
+        if "file" in val:
+            # XXX: Is it completely safe to assume static?
+            value = expand.read_files([val["file"]], root_dir)
+            _set_config(dist, "license", _static.Str(value))
+            dist._referenced_files.add(val["file"])
+        else:
+            _set_config(dist, "license", _static.Str(val["text"]))
 
 
 def _people(dist: Distribution, val: list[dict], _root_dir: StrPath | None, kind: str):

setuptools/dist.py

@@ -12,6 +12,7 @@
 from typing import TYPE_CHECKING, Any, Union
 
 from more_itertools import partition, unique_everseen
+from packaging.licenses import canonicalize_license_expression
 from packaging.markers import InvalidMarker, Marker
 from packaging.specifiers import InvalidSpecifier, SpecifierSet
 from packaging.version import Version
@@ -288,6 +289,7 @@ class Distribution(_Distribution):
         'long_description_content_type': lambda: None,
         'project_urls': dict,
         'provides_extras': dict,  # behaves like an ordered set
+        'license_expression': lambda: None,
         'license_file': lambda: None,
         'license_files': lambda: None,
         'install_requires': list,
@@ -402,6 +404,31 @@ def _normalize_requires(self):
             (k, list(map(str, _reqs.parse(v or [])))) for k, v in extras_require.items()
         )
 
+    def _finalize_license_expression(self) -> None:
+        """Normalize license and license_expression."""
+        license_expr = self.metadata.license_expression
+        if license_expr:
+            normalized = canonicalize_license_expression(license_expr)
+            if license_expr != normalized:
+                InformationOnly.emit(f"Normalizing '{license_expr}' to '{normalized}'")
+                self.metadata.license_expression = normalized
+
+            classifiers = []
+            license_classifiers_found = False
+            for cl in self.metadata.get_classifiers():
+                if not cl.startswith("License :: "):
+                    classifiers.append(cl)
+                    continue
+                license_classifiers_found = True
+                SetuptoolsDeprecationWarning.emit(
+                    "License classifier are deprecated in favor of the license expression.",
+                    f"Please remove the '{cl}' classifier.",
+                    see_url="https://peps.python.org/pep-0639/",
+                    due_date=(2027, 2, 17),  # Introduced 2025-02-17
+                )
+            if license_classifiers_found:
+                self.metadata.set_classifiers(classifiers)
+
     def _finalize_license_files(self) -> None:
         """Compute names of all license files which should be included."""
         license_files: list[str] | None = self.metadata.license_files
@@ -655,6 +682,7 @@ def parse_config_files(
             pyprojecttoml.apply_configuration(self, filename, ignore_option_errors)
 
         self._finalize_requires()
+        self._finalize_license_expression()
         self._finalize_license_files()
 
     def fetch_build_eggs(

setuptools/tests/config/test_apply_pyprojecttoml.py

@@ -9,6 +9,7 @@
 import io
 import re
 import tarfile
+import warnings
 from inspect import cleandoc
 from pathlib import Path
 from unittest.mock import Mock
@@ -24,6 +25,7 @@
 from setuptools.config._apply_pyprojecttoml import _MissingDynamic, _some_attrgetter
 from setuptools.dist import Distribution
 from setuptools.errors import RemovedConfigError
+from setuptools.warnings import SetuptoolsDeprecationWarning
 
 from .downloads import retrieve_file, urls_from_file
 
@@ -156,6 +158,32 @@ def main_gui(): pass
 def main_tomatoes(): pass
 """
 
+PEP639_LICENSE_TEXT = """\
+[project]
+name = "spam"
+version = "2020.0.0"
+authors = [
+  {email = "hi@pradyunsg.me"},
+  {name = "Tzu-Ping Chung"}
+]
+license = {text = "MIT"}
+"""
+
+PEP639_LICENSE_EXPRESSION = """\
+[project]
+name = "spam"
+version = "2020.0.0"
+authors = [
+  {email = "hi@pradyunsg.me"},
+  {name = "Tzu-Ping Chung"}
+]
+license = "mit or apache-2.0"  # should be normalized in metadata
+classifiers = [
+    "Development Status :: 5 - Production/Stable",
+    "Programming Language :: Python",
+]
+"""
+
 
 def _pep621_example_project(
     tmp_path,
@@ -251,10 +279,69 @@ def test_utf8_maintainer_in_metadata(  # issue-3663
     assert f"Maintainer-email: {expected_maintainers_meta_value}" in content
 
 
-class TestLicenseFiles:
-    # TODO: After PEP 639 is accepted, we have to move the license-files
-    #       to the `project` table instead of `tool.setuptools`
+@pytest.mark.parametrize(
+    ('pyproject_text', 'license', 'license_expression', 'content_str'),
+    (
+        pytest.param(
+            PEP639_LICENSE_TEXT,
+            'MIT',
+            None,
+            'License: MIT',
+            id='license-text',
+        ),
+        pytest.param(
+            PEP639_LICENSE_EXPRESSION,
+            None,
+            'MIT OR Apache-2.0',
+            'License: MIT OR Apache-2.0',  # TODO Metadata version '2.4'
+            id='license-expression',
+        ),
+    ),
+)
+def test_license_in_metadata(
+    license,
+    license_expression,
+    content_str,
+    pyproject_text,
+    tmp_path,
+):
+    pyproject = _pep621_example_project(
+        tmp_path,
+        "README",
+        pyproject_text=pyproject_text,
+    )
+    dist = pyprojecttoml.apply_configuration(makedist(tmp_path), pyproject)
+    assert dist.metadata.license == license
+    assert dist.metadata.license_expression == license_expression
+    pkg_file = tmp_path / "PKG-FILE"
+    with open(pkg_file, "w", encoding="utf-8") as fh:
+        dist.metadata.write_pkg_file(fh)
+    content = pkg_file.read_text(encoding="utf-8")
+    assert content_str in content
+
+
+def test_license_expression_with_bad_classifier(tmp_path):
+    text = PEP639_LICENSE_EXPRESSION.rsplit("\n", 2)[0]
+    pyproject = _pep621_example_project(
+        tmp_path,
+        "README",
+        f"{text}\n    \"License :: OSI Approved :: MIT License\"\n]",
+    )
+    msg = "License classifier are deprecated(?:.|\n)*'License :: OSI Approved :: MIT License'"
+    with pytest.raises(SetuptoolsDeprecationWarning, match=msg):
+        pyprojecttoml.apply_configuration(makedist(tmp_path), pyproject)
 
+    with warnings.catch_warnings():
+        warnings.simplefilter("ignore", SetuptoolsDeprecationWarning)
+        dist = pyprojecttoml.apply_configuration(makedist(tmp_path), pyproject)
+        # Check 'License :: OSI Approved :: MIT License' is removed
+        assert dist.metadata.get_classifiers() == [
+            "Development Status :: 5 - Production/Stable",
+            "Programming Language :: Python",
+        ]
+
+
+class TestLicenseFiles:
     def base_pyproject(self, tmp_path, additional_text):
         pyproject = _pep621_example_project(tmp_path, "README")
         text = pyproject.read_text(encoding="utf-8")
@@ -267,6 +354,24 @@ def base_pyproject(self, tmp_path, additional_text):
         pyproject.write_text(text, encoding="utf-8")
         return pyproject
 
+    def base_pyproject_license_pep639(self, tmp_path):
+        pyproject = _pep621_example_project(tmp_path, "README")
+        text = pyproject.read_text(encoding="utf-8")
+
+        # Sanity-check
+        assert 'license = {file = "LICENSE.txt"}' in text
+        assert 'license-files' not in text
+        assert "[tool.setuptools]" not in text
+
+        text = re.sub(
+            r"(license = {file = \"LICENSE.txt\"})\n",
+            ("license = \"licenseref-Proprietary\"\nlicense-files = [\"_FILE*\"]\n"),
+            text,
+            count=1,
+        )
+        pyproject.write_text(text, encoding="utf-8")
+        return pyproject
+
     def test_both_license_and_license_files_defined(self, tmp_path):
         setuptools_config = '[tool.setuptools]\nlicense-files = ["_FILE*"]'
         pyproject = self.base_pyproject(tmp_path, setuptools_config)
@@ -283,6 +388,18 @@ def test_both_license_and_license_files_defined(self, tmp_path):
         assert set(dist.metadata.license_files) == {"_FILE.rst", "_FILE.txt"}
         assert dist.metadata.license == "LicenseRef-Proprietary\n"
 
+    def test_both_license_and_license_files_defined_pep639(self, tmp_path):
+        # Set license and license-files
+        pyproject = self.base_pyproject_license_pep639(tmp_path)
+
+        (tmp_path / "_FILE.txt").touch()
+        (tmp_path / "_FILE.rst").touch()
+
+        dist = pyprojecttoml.apply_configuration(makedist(tmp_path), pyproject)
+        assert set(dist.metadata.license_files) == {"_FILE.rst", "_FILE.txt"}
+        assert dist.metadata.license is None
+        assert dist.metadata.license_expression == "LicenseRef-Proprietary"
+
     def test_default_patterns(self, tmp_path):
         setuptools_config = '[tool.setuptools]\nzip-safe = false'
         # ^ used just to trigger section validation