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`

pyproject.toml

@@ -11,10 +11,10 @@ authors = [
 ]
 description = "Easily download, build, install, upgrade, and uninstall Python packages"
 readme = "README.rst"
+license = "MIT"
 classifiers = [
 	"Development Status :: 5 - Production/Stable",
 	"Intended Audience :: Developers",
-	"License :: OSI Approved :: MIT License",
 	"Programming Language :: Python :: 3",
 	"Programming Language :: Python :: 3 :: Only",
 	"Topic :: Software Development :: Libraries :: Python Modules",

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'):
@@ -175,9 +176,12 @@ def write_field(key, value):
         if attr_val is not None:
             write_field(field, attr_val)
 
-    license = self.get_license()
-    if license:
-        write_field('License', rfc822_escape(license))
+    if self.license_expression:
+        write_field('License-Expression', rfc822_escape(self.license_expression))
+    else:
+        license = self.get_license()
+        if license:
+            write_field('License', rfc822_escape(license))
 
     for label, url in self.project_urls.items():
         write_field('Project-URL', f'{label}, {url}')

setuptools/config/_apply_pyprojecttoml.py

@@ -181,16 +181,19 @@ 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

@@ -288,6 +288,7 @@ 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,

setuptools/tests/config/test_apply_pyprojecttoml.py

@@ -156,6 +156,28 @@ 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"
+"""
+
 
 def _pep621_example_project(
     tmp_path,
@@ -251,6 +273,47 @@ def test_utf8_maintainer_in_metadata(  # issue-3663
     assert f"Maintainer-email: {expected_maintainers_meta_value}" in content
 
 
+@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',
+            'License-Expression: MIT',
+            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
+
+
 class TestLicenseFiles:
     # TODO: After PEP 639 is accepted, we have to move the license-files
     #       to the `project` table instead of `tool.setuptools`