Add more robust license file installation

- Expand default license file inclusion globs. This uses the same
  patterns as setuptools/wheel with the addition of 'LICENSES/*.txt' for
  REUSE.
- Ensure matching license files are always included in sdists.
- Warn users when no license files are detected.
- Add unit tests

flit_core/flit_core/config.py

@@ -21,6 +21,9 @@
 
 log = logging.getLogger(__name__)
 
+# These are the same patterns used by setuptools/wheel
+# besides `LICENSES/*.txt` which is from the REUSE specification
+LICENSE_PATTERNS = ('AUTHORS*', 'COPYING*', 'LICEN[CS]E*', 'LICENSES/*.txt')
 
 class ConfigError(ValueError):
     pass
@@ -257,6 +260,7 @@ def __init__(self):
         self.sdist_exclude_patterns = []
         self.dynamic_metadata = []
         self.data_directory = None
+        self.license_files = []
 
     def add_scripts(self, scripts_dict):
         if scripts_dict:
@@ -401,6 +405,8 @@ def _prep_metadata(md_sect, path):
     # For internal use, record the main requirements as a '.none' extra.
     res.reqs_by_extra['.none'] = reqs_noextra
 
+    res.license_files = find_licenses(path.parent if path else Path("."))
+
     return res
 
 def _expand_requires_extra(re):
@@ -506,7 +512,7 @@ def read_pep621_metadata(proj, path) -> LoadedConfig:
                 "Unrecognised keys in [project.license]: {}".format(unrec_keys)
             )
 
-        # TODO: Do something with license info.
+        # TODO: Include license info in the metadata.
         # The 'License' field in packaging metadata is a brief description of
         # a license, not the full text or a file path. PEP 639 will improve on
         # how licenses are recorded.
@@ -515,13 +521,15 @@ def read_pep621_metadata(proj, path) -> LoadedConfig:
                 raise ConfigError(
                     "[project.license] should specify file or text, not both"
                 )
-            lc.referenced_files.append(license_tbl['file'])
+            lc.license_files.append(Path(license_tbl['file']))
         elif 'text' in license_tbl:
             pass
         else:
             raise ConfigError(
                 "file or text field required in [project.license] table"
             )
+    if not lc.license_files:
+        lc.license_files = find_licenses(path.parent)
 
     if 'authors' in proj:
         _check_type(proj, 'authors', list)
@@ -658,3 +666,11 @@ def pep621_people(people, group_name='author') -> dict:
     if emails:
         res[group_name + '_email'] = ", ".join(emails)
     return res
+
+def find_licenses(path):
+    found = []
+    for pattern in LICENSE_PATTERNS:
+        found.extend(file for file in path.glob(pattern) if file.is_file())
+    if not found:
+        log.warning("No licenses were found in %s. Add a license!", LICENSE_PATTERNS)
+    return found

flit_core/flit_core/sdist.py

@@ -91,7 +91,8 @@ def from_ini_path(cls, ini_path: Path):
         srcdir = ini_path.parent
         module = common.Module(ini_info.module, srcdir)
         metadata = common.make_metadata(module, ini_info)
-        extra_files = [ini_path.name] + ini_info.referenced_files
+        license_files = list(map(str, ini_info.license_files))
+        extra_files = [ini_path.name] + ini_info.referenced_files + license_files
         return cls(
             module, metadata, srcdir, ini_info.reqs_by_extra,
             ini_info.entrypoints, extra_files, ini_info.data_directory,

flit_core/flit_core/tests/test_config.py

@@ -163,3 +163,20 @@ def test_bad_pep621_readme(readme, err_match):
     }
     with pytest.raises(config.ConfigError, match=err_match):
         config.read_pep621_metadata(proj, samples_dir / 'pep621')
+
+def test_license_file_auto_detect(tmp_path):
+    proj = {'name': 'module1', 'version': '1.0', 'description': 'x'}
+    tmp_path.joinpath('module1').mkdir()
+    for file in ('LICENSE', 'COPYING.md', 'module1/__init__.py'):
+        tmp_path.joinpath(file).touch()
+    parsed_config = config.read_pep621_metadata(proj, tmp_path / "pyproject.toml")
+    assert parsed_config.license_files == [tmp_path / 'COPYING.md', tmp_path / 'LICENSE']
+
+def test_missing_license_warning(tmp_path, caplog):
+    proj = {'name': 'module1', 'version': '1.0', 'description': 'x'}
+    tmp_path.joinpath('module1').mkdir()
+    for file in ('module1/__init__.py',):
+        tmp_path.joinpath(file).touch()
+    config.read_pep621_metadata(proj, tmp_path / 'pyproject.toml')
+    message = f"No licenses were found in {config.LICENSE_PATTERNS}. Add a license!"
+    assert message in caplog.messages

flit_core/flit_core/wheel.py

@@ -60,7 +60,8 @@ def zip_timestamp_from_env() -> Optional[tuple]:
 
 class WheelBuilder:
     def __init__(
-            self, directory, module, metadata, entrypoints, target_fp, data_directory
+            self, directory, module, metadata, entrypoints, target_fp, data_directory,
+            license_files
     ):
         """Build a wheel from a module/package
         """
@@ -69,6 +70,7 @@ def __init__(
         self.metadata = metadata
         self.entrypoints = entrypoints
         self.data_directory = data_directory
+        self.license_files = license_files
 
         self.records = []
         self.source_time_stamp = zip_timestamp_from_env()
@@ -86,7 +88,8 @@ def from_ini_path(cls, ini_path, target_fp):
         module = common.Module(ini_info.module, directory)
         metadata = common.make_metadata(module, ini_info)
         return cls(
-            directory, module, metadata, entrypoints, target_fp, ini_info.data_directory
+            directory, module, metadata, entrypoints, target_fp, ini_info.data_directory,
+            ini_info.license_files
         )
 
     @property
@@ -181,10 +184,8 @@ def write_metadata(self):
             with self._write_to_zip(self.dist_info + '/entry_points.txt') as f:
                 common.write_entry_points(self.entrypoints, f)
 
-        for base in ('COPYING', 'LICENSE'):
-            for path in sorted(self.directory.glob(base + '*')):
-                if path.is_file():
-                    self._add_file(path, '%s/%s' % (self.dist_info, path.name))
+        for path in self.license_files:
+            self._add_file(path, '%s/%s' % (self.dist_info, path.name))
 
         with self._write_to_zip(self.dist_info + '/WHEEL') as f:
             _write_wheel_file(f, supports_py2=self.metadata.supports_py2)