Accept License-Expression in metadata (PEP 639)

[PEP 639](https://peps.python.org/pep-0639/) adds the
`License-Expression` header. This commit adds support for it in the
metadata parser.

Twisted 23.8.0 has already replaced the `Licence` header with
`License-Expression` and thus is read as an `UNKNOWN` license.

Signed-off-by: Aurélien Bompard <[email protected]>

Author: abompard

liccheck/command_line.py

@@ -141,7 +141,7 @@ class Reason(enum.Enum):
 
 
 def get_packages_info(requirement_file, no_deps=False):
-    regex_license = re.compile(r"License: (?P<license>.*)?$", re.M)
+    regex_license = re.compile(r"License(?:-Expression)?: (?P<license>.*)?$", re.M)
     regex_classifier = re.compile(
         r"Classifier: License(?: :: OSI Approved)?(?: :: (?P<classifier>.*))?$", re.M
     )

tests/test_get_packages_info.py

@@ -1,5 +1,6 @@
 import sys
 
+import pkg_resources
 import pytest
 
 from liccheck.command_line import get_packages_info
@@ -59,3 +60,21 @@ def test_deps(tmpfile, no_deps, expected_packages):
     packages_info = get_packages_info(tmppath, no_deps)
     packages = tuple(package['name'] for package in packages_info)
     assert packages == expected_packages
+
+
+def test_license_expression(tmp_path, mocker):
+    resolve = mocker.patch("liccheck.command_line.resolve")
+    req_path = tmp_path.joinpath("requirements.txt").as_posix()
+    with open(req_path, "w") as tmpfh:
+        tmpfh.write("Twisted\n")
+    pkg_info_path = tmp_path.joinpath("PKG-INFO").as_posix()
+    with open(pkg_info_path, "w") as tmpfh:
+        tmpfh.write("Metadata-Version: 2.1\n")
+        tmpfh.write("Name: Twisted\n")
+        tmpfh.write("Version: 23.8.0\n")
+        tmpfh.write("License-Expression: MIT\n")
+    metadata = pkg_resources.FileMetadata(pkg_info_path)
+    resolve.return_value = [
+        pkg_resources.Distribution(project_name="Twisted", metadata=metadata)
+    ]
+    assert get_packages_info(req_path)[0]["licenses"] == ["MIT"]