Add warning for deprecated project.license as TOML table (PEP 639-related)

newsfragments/4840.feature.rst

@@ -0,0 +1,5 @@
+Deprecated ``project.license`` as a TOML table in
+``pyproject.toml``. Users are expected to move towards using
+``project.license-files`` and/or SPDX expressions (as strings) in
+``pyproject.license``.
+See :pep:`PEP 639 <639#deprecate-license-key-table-subkeys>`.

setuptools/config/_apply_pyprojecttoml.py

@@ -203,6 +203,14 @@ def _license(dist: Distribution, val: str | dict, root_dir: StrPath | None):
     if isinstance(val, str):
         _set_config(dist, "license_expression", _static.Str(val))
     else:
+        pypa_guides = "guides/writing-pyproject-toml/#license"
+        SetuptoolsDeprecationWarning.emit(
+            "`project.license` as a TOML table is deprecated",
+            "Please use a simple string containing a SPDX expression for "
+            "`project.license`. You can also use `project.license-files`.",
+            see_url=f"https://packaging.python.org/en/latest/{pypa_guides}",
+            due_date=(2026, 2, 18),  # Introduced on 2025-02-18
+        )
         if "file" in val:
             # XXX: Is it completely safe to assume static?
             value = expand.read_files([val["file"]], root_dir)

setuptools/tests/config/test_apply_pyprojecttoml.py

@@ -93,7 +93,7 @@ def test_apply_pyproject_equivalent_to_setupcfg(url, monkeypatch, tmp_path):
 description = "Lovely Spam! Wonderful Spam!"
 readme = "README.rst"
 requires-python = ">=3.8"
-license = {file = "LICENSE.txt"}
+license-files = ["LICENSE.txt"]  # Updated to be PEP 639 compliant
 keywords = ["egg", "bacon", "sausage", "tomatoes", "Lobster Thermidor"]
 authors = [
   {email = "[email protected]"},
@@ -206,7 +206,6 @@ def test_pep621_example(tmp_path):
     """Make sure the example in PEP 621 works"""
     pyproject = _pep621_example_project(tmp_path)
     dist = pyprojecttoml.apply_configuration(makedist(tmp_path), pyproject)
-    assert dist.metadata.license == "--- LICENSE stub ---"
     assert set(dist.metadata.license_files) == {"LICENSE.txt"}
 
 
@@ -294,6 +293,11 @@ def test_utf8_maintainer_in_metadata(  # issue-3663
             'License: MIT',
             'License-Expression: ',
             id='license-text',
+            marks=[
+                pytest.mark.filterwarnings(
+                    "ignore:.project.license. as a TOML table is deprecated",
+                )
+            ],
         ),
         pytest.param(
             PEP639_LICENSE_EXPRESSION,
@@ -354,47 +358,51 @@ def test_license_classifier_without_license_expression(tmp_path):
     """
     pyproject = _pep621_example_project(tmp_path, "README", text)
 
-    msg = "License classifiers are deprecated(?:.|\n)*MIT License"
-    with pytest.warns(SetuptoolsDeprecationWarning, match=msg):
+    msg1 = "License classifiers are deprecated(?:.|\n)*MIT License"
+    msg2 = ".project.license. as a TOML table is deprecated"
+    with (
+        pytest.warns(SetuptoolsDeprecationWarning, match=msg1),
+        pytest.warns(SetuptoolsDeprecationWarning, match=msg2),
+    ):
         dist = pyprojecttoml.apply_configuration(makedist(tmp_path), pyproject)
 
     # Check license classifier is still included
     assert dist.metadata.get_classifiers() == ["License :: OSI Approved :: MIT License"]
 
 
 class TestLicenseFiles:
-    def base_pyproject(self, tmp_path, additional_text):
-        pyproject = _pep621_example_project(tmp_path, "README")
-        text = pyproject.read_text(encoding="utf-8")
-
-        # Sanity-check
-        assert 'license = {file = "LICENSE.txt"}' in text
-        assert "[tool.setuptools]" not in text
-
-        text = f"{text}\n{additional_text}\n"
-        pyproject.write_text(text, encoding="utf-8")
-        return pyproject
-
-    def base_pyproject_license_pep639(self, tmp_path, additional_text=""):
-        pyproject = _pep621_example_project(tmp_path, "README")
-        text = pyproject.read_text(encoding="utf-8")
+    def base_pyproject(
+        self,
+        tmp_path,
+        additional_text="",
+        license_toml='license = {file = "LICENSE.txt"}\n',
+    ):
+        text = PEP639_LICENSE_EXPRESSION
 
         # Sanity-check
-        assert 'license = {file = "LICENSE.txt"}' in text
+        assert 'license = "mit or apache-2.0"' 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"),
+            r"(license = .*)\n",
+            license_toml,
             text,
             count=1,
         )
-        if additional_text:
-            text = f"{text}\n{additional_text}\n"
-        pyproject.write_text(text, encoding="utf-8")
+        assert license_toml in text  # sanity check
+        text = f"{text}\n{additional_text}\n"
+        pyproject = _pep621_example_project(tmp_path, "README", pyproject_text=text)
         return pyproject
 
+    def base_pyproject_license_pep639(self, tmp_path, additional_text=""):
+        return self.base_pyproject(
+            tmp_path,
+            additional_text=additional_text,
+            license_toml='license = "licenseref-Proprietary"'
+            '\nlicense-files = ["_FILE*"]\n',
+        )
+
     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)
@@ -407,8 +415,12 @@ def test_both_license_and_license_files_defined(self, tmp_path):
         license = tmp_path / "LICENSE.txt"
         license.write_text("LicenseRef-Proprietary\n", encoding="utf-8")
 
-        msg = "'tool.setuptools.license-files' is deprecated in favor of 'project.license-files'"
-        with pytest.warns(SetuptoolsDeprecationWarning, match=msg):
+        msg1 = "'tool.setuptools.license-files' is deprecated in favor of 'project.license-files'"
+        msg2 = ".project.license. as a TOML table is deprecated"
+        with (
+            pytest.warns(SetuptoolsDeprecationWarning, match=msg1),
+            pytest.warns(SetuptoolsDeprecationWarning, match=msg2),
+        ):
             dist = pyprojecttoml.apply_configuration(makedist(tmp_path), pyproject)
         assert set(dist.metadata.license_files) == {"_FILE.rst", "_FILE.txt"}
         assert dist.metadata.license == "LicenseRef-Proprietary\n"
@@ -437,17 +449,35 @@ def test_license_files_defined_twice(self, tmp_path):
     def test_default_patterns(self, tmp_path):
         setuptools_config = '[tool.setuptools]\nzip-safe = false'
         # ^ used just to trigger section validation
-        pyproject = self.base_pyproject(tmp_path, setuptools_config)
+        pyproject = self.base_pyproject(tmp_path, setuptools_config, license_toml="")
 
         license_files = "LICENCE-a.html COPYING-abc.txt AUTHORS-xyz NOTICE,def".split()
 
         for fname in license_files:
             (tmp_path / fname).write_text(f"{fname}\n", encoding="utf-8")
 
         dist = pyprojecttoml.apply_configuration(makedist(tmp_path), pyproject)
+
         assert (tmp_path / "LICENSE.txt").exists()  # from base example
         assert set(dist.metadata.license_files) == {*license_files, "LICENSE.txt"}
 
+    def test_deprecated_file_expands_to_text(self, tmp_path):
+        """Make sure the old example with ``license = {text = ...}`` works"""
+
+        assert 'license-files = ["LICENSE.txt"]' in PEP621_EXAMPLE  # sanity check
+        text = PEP621_EXAMPLE.replace(
+            'license-files = ["LICENSE.txt"]',
+            'license = {file = "LICENSE.txt"}',
+        )
+        pyproject = _pep621_example_project(tmp_path, pyproject_text=text)
+
+        msg = ".project.license. as a TOML table is deprecated"
+        with pytest.warns(SetuptoolsDeprecationWarning, match=msg):
+            dist = pyprojecttoml.apply_configuration(makedist(tmp_path), pyproject)
+
+        assert dist.metadata.license == "--- LICENSE stub ---"
+        assert set(dist.metadata.license_files) == {"LICENSE.txt"}  # auto-filled
+
 
 class TestPyModules:
     # https://github.com/pypa/setuptools/issues/4316

setuptools/tests/test_build_meta.py

@@ -387,9 +387,13 @@ def test_build_with_pyproject_config(self, tmpdir, setup_script):
         build_backend = self.get_build_backend()
         with tmpdir.as_cwd():
             path.build(files)
+            msgs = [
+                "'tool.setuptools.license-files' is deprecated in favor of 'project.license-files'",
+                "`project.license` as a TOML table is deprecated",
+            ]
             with warnings.catch_warnings():
-                msg = "'tool.setuptools.license-files' is deprecated in favor of 'project.license-files'"
-                warnings.filterwarnings("ignore", msg, SetuptoolsDeprecationWarning)
+                for msg in msgs:
+                    warnings.filterwarnings("ignore", msg, SetuptoolsDeprecationWarning)
                 sdist_path = build_backend.build_sdist("temp")
                 wheel_file = build_backend.build_wheel("temp")
 

setuptools/tests/test_sdist.py

@@ -708,12 +708,21 @@ def test_sdist_with_latin1_encoded_filename(self):
             [project]
             name = "testing"
             readme = "USAGE.rst"
-            license = {file = "DOWHATYOUWANT"}
+            license-files = ["DOWHATYOUWANT"]
             dynamic = ["version"]
             [tool.setuptools.dynamic]
             version = {file = ["src/VERSION.txt"]}
             """,
         "pyproject.toml - directive with str instead of list": """
+            [project]
+            name = "testing"
+            readme = "USAGE.rst"
+            license-files = ["DOWHATYOUWANT"]
+            dynamic = ["version"]
+            [tool.setuptools.dynamic]
+            version = {file = "src/VERSION.txt"}
+            """,
+        "pyproject.toml - deprecated license table with file entry": """
             [project]
             name = "testing"
             readme = "USAGE.rst"
@@ -725,6 +734,9 @@ def test_sdist_with_latin1_encoded_filename(self):
     }
 
     @pytest.mark.parametrize("config", _EXAMPLE_DIRECTIVES.keys())
+    @pytest.mark.filterwarnings(
+        "ignore:.project.license. as a TOML table is deprecated"
+    )
     def test_add_files_referenced_by_config_directives(self, source_dir, config):
         config_file, _, _ = config.partition(" - ")
         config_text = self._EXAMPLE_DIRECTIVES[config]