Normalize specifier version for prefix matching

In case of prefix version matching, normalization of the version was not applied to the specifier's version.
This resulted in `2` being rejected as a candidate for `==0!2.*`
With normalization applied, the candidate is now accepted.

packaging/specifiers.py

@@ -266,9 +266,12 @@ def _compare_equal(self, prospective: Version, spec: str) -> bool:
         if spec.endswith(".*"):
             # In the case of prefix matching we want to ignore local segment.
             prospective = Version(prospective.public)
+            # Convert our spec string into a Version ignoring the trailing .*
+            # This allows to get the normalized version string
+            spec_version = Version(spec[:-2])
             # Split the spec out by dots, and pretend that there is an implicit
             # dot in between a release segment and a pre-release segment.
-            split_spec = _version_split(spec[:-2])  # Remove the trailing .*
+            split_spec = _version_split(str(spec_version))
 
             # Split the prospective version out by dots, and pretend that there
             # is an implicit dot in between a release segment and a pre-release

tests/test_specifiers.py

@@ -302,10 +302,14 @@ def test_comparison_non_specifier(self):
                 ("2c1.post1.dev1", "==2.*"),
                 ("2rc1", "==2.*"),
                 ("2", "==2.*"),
+                ("2", "==0!2.*"),
+                ("0!2", "==2.*"),
                 ("2.0", "==2.*"),
                 ("2.0.0", "==2.*"),
                 ("2.0.post1", "==2.0.post1.*"),
                 ("2.0.post1.dev1", "==2.0.post1.*"),
+                ("2.0.rc1", "==2.0.c1.*"),
+                ("2.0.rc1.post1", "==2.0.c1.*"),
                 ("2.1+local.version", "==2.1.*"),
                 # Test the in-equality operation
                 ("2.1", "!=2"),