Make license declarations explicit

__init__.py

@@ -4,6 +4,8 @@
     'importlib_resources; python_version < "3.12"',
 ]
 
+__license__ = 'Apache-2.0'
+
 # honor PYTHONSAFEPATH (coherent-oss/system#21)
 import jaraco.compat.py310.safe_path  # noqa: F401
 

discovery.py

@@ -201,10 +201,10 @@ def declared_license():
 
     Returns None if no ``__license__`` is declared.
 
-    >>> declared_license()
     >>> monkeypatch = getfixture('monkeypatch')
     >>> tmp_path = getfixture('tmp_path')
     >>> monkeypatch.chdir(tmp_path)
+    >>> declared_license()
     >>> _ = (tmp_path / '__init__.py').write_text('__license__ = "MIT"\\n')
     >>> declared_license()
     'MIT'

flit.py

@@ -113,4 +113,5 @@ def gen_files(self):
         yield from super().gen_files()
         yield 'pyproject.toml', render(self.metadata)
         yield self.metadata.readme_filename, self.metadata['Description']
-        yield 'LICENSE', coherent.licensed.resolve(self.metadata['License-Expression'])
+        if license := self.metadata['License-Expression']:
+            yield 'LICENSE', coherent.licensed.resolve(license)

metadata.py

@@ -112,7 +112,8 @@ def _discover_fields():
         yield from discovery.best_description()
         for classifier in discovery.generate_classifiers():
             yield 'Classifier', classifier
-        yield 'License-Expression', discovery.declared_license() or 'Apache-2.0'
+        if license := discovery.declared_license():
+            yield 'License-Expression', license
 
     @classmethod
     @suppress(MetadataNotFound)
@@ -153,8 +154,9 @@ def render_toml(self):
             "dependencies": self.get_all("Requires-Dist") or [],
             "classifiers": self.get_all("Classifier") or [],
             'urls': self.urls,
-            'license': self['License-Expression'],
         }
+        if license := self['License-Expression']:
+            project['license'] = license
 
         return project