Fix prefix version matching (pypa#564)

0-padding shall only be applied on the prospective version, before shortening,
in order to get the correct shortened prospective version.

packaging/specifiers.py

@@ -380,7 +380,7 @@ def _compare_equal(self, prospective: Version, spec: str) -> bool:
         # We need special logic to handle prefix matching
         if spec.endswith(".*"):
             # In the case of prefix matching we want to ignore local segment.
-            prospective = Version(prospective.public)
+            normalized_prospective = canonicalize_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
@@ -390,20 +390,18 @@ def _compare_equal(self, prospective: Version, spec: str) -> bool:
             # Split the prospective version out by dots, and pretend that there
             # is an implicit dot in between a release segment and a pre-release
             # segment.
-            split_prospective = _version_split(str(prospective))
+            split_prospective = _version_split(normalized_prospective)
+
+            # 0-pad the prospective version before shortening it to get the correct
+            # shortened version.
+            padded_prospective, _ = _pad_version(split_prospective, split_spec)
 
             # Shorten the prospective version to be the same length as the spec
             # so that we can determine if the specifier is a prefix of the
             # prospective version or not.
-            shortened_prospective = split_prospective[: len(split_spec)]
-
-            # Pad out our two sides with zeros so that they both equal the same
-            # length.
-            padded_spec, padded_prospective = _pad_version(
-                split_spec, shortened_prospective
-            )
+            shortened_prospective = padded_prospective[: len(split_spec)]
 
-            return padded_prospective == padded_spec
+            return shortened_prospective == split_spec
         else:
             # Convert our spec string into a Version
             spec_version = Version(spec)

tests/test_specifiers.py

@@ -307,8 +307,11 @@ def test_comparison_non_specifier(self):
                 ("2b1.dev1", "==2.*"),
                 ("2c1", "==2.*"),
                 ("2c1.post1.dev1", "==2.*"),
+                ("2c1.post1.dev1", "==2.0.*"),
                 ("2rc1", "==2.*"),
+                ("2rc1", "==2.0.*"),
                 ("2", "==2.*"),
+                ("2", "==2.0.*"),
                 ("2", "==0!2.*"),
                 ("0!2", "==2.*"),
                 ("2.0", "==2.*"),
@@ -405,8 +408,11 @@ def test_comparison_non_specifier(self):
                 ("2b1.dev1", "!=2.*"),
                 ("2c1", "!=2.*"),
                 ("2c1.post1.dev1", "!=2.*"),
+                ("2c1.post1.dev1", "!=2.0.*"),
                 ("2rc1", "!=2.*"),
+                ("2rc1", "!=2.0.*"),
                 ("2", "!=2.*"),
+                ("2", "!=2.0.*"),
                 ("2.0", "!=2.*"),
                 ("2.0.0", "!=2.*"),
                 # Test the greater than equal operation