Normalize specifier version for prefix matching (pypa#561)

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

@@ -381,9 +381,11 @@ 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)
+            # Get the normalized version string ignoring the trailing .*
+            normalized_spec = canonicalize_version(spec[:-2], strip_trailing_zero=False)
             # 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(normalized_spec)
 
             # 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

@@ -309,6 +309,8 @@ 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.*"),
                 ("2.1+local.version", "==2.1.*"),
@@ -358,6 +360,7 @@ def test_comparison_non_specifier(self):
                 ("1.1", "~=1.0"),
                 ("1.9999999", "~=1.0"),
                 ("1.1", "~=1.0a1"),
+                ("2022.01.01", "~=2022.01.01"),
                 # Test that epochs are handled sanely
                 ("2!1.0", "~=2!1.0"),
                 ("2!1.0", "==2!1.*"),