Fix prefix version matching

Use a different padding depending on the specifier having a pre-release/post-release segment or not in order to get the correct shortened prospective version.

packaging/specifiers.py

@@ -278,18 +278,24 @@ def _compare_equal(self, prospective: Version, spec: str) -> bool:
             # segment.
             split_prospective = _version_split(str(prospective))
 
+            if spec_version.is_prerelease or spec_version.is_postrelease:
+                # the release segment must match exactly
+                # 0-pad both the prospective and spec versions
+                padded_spec, padded_prospective = _pad_version(
+                    split_spec, split_prospective
+                )
+            else:
+                # 0-pad the prospective version before shortening it to get the correct
+                # shortened version.
+                _, padded_prospective = _pad_version(split_spec, split_prospective)
+                padded_spec = 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(padded_spec)]
 
-            return padded_prospective == padded_spec
+            return shortened_prospective == padded_spec
         else:
             # Convert our spec string into a Version
             spec_version = Version(spec)

tests/test_specifiers.py

@@ -300,16 +300,34 @@ 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.*"),
                 ("2.0.0", "==2.*"),
                 ("2.0.post1", "==2.0.post1.*"),
+                ("2.post1", "==2.0.post1.*"),
+                ("2.0.post1", "==2.post1.*"),
                 ("2.0.post1.dev1", "==2.0.post1.*"),
+                ("2.post1.dev1", "==2.0.post1.*"),
+                ("2.0.post1.dev1", "==2.post1.*"),
                 ("2.0.rc1", "==2.0.c1.*"),
                 ("2.0.rc1.post1", "==2.0.c1.*"),
+                ("2rc1", "==2.0c1.*"),
+                ("2.0rc1", "==2c1.*"),
+                ("2.0rc1.post1.dev1", "==2.0c1.*"),
+                ("2rc1.post1.dev1", "==2.0c1.*"),
+                ("2.0rc1.post1.dev1", "==2c1.*"),
+                ("2.0rc1.post0", "==2.0c1.post.*"),
+                ("2rc1.post0", "==2.0c1.post.*"),
+                ("2.0rc1.post0", "==2c1.post.*"),
+                ("2.0rc1.post0.dev1", "==2.0c1.post.*"),
+                ("2rc1.post0.dev1", "==2.0c1.post.*"),
+                ("2.0rc1.post0.dev1", "==2c1.post.*"),
                 ("2.1+local.version", "==2.1.*"),
                 # Test the in-equality operation
                 ("2.1", "!=2"),
@@ -382,6 +400,9 @@ def test_comparison_non_specifier(self):
                 # Test the equality operation with a prefix
                 ("2.0", "==3.*"),
                 ("2.1", "==2.0.*"),
+                ("2.0rc1", "==2.0rc.*"),
+                ("2.0.post1", "==2.0.post.*"),
+                ("2.0rc1.post1", "==2.0rc1.post.*"),
                 # Test the in-equality operation
                 ("2.0", "!=2"),
                 ("2.0", "!=2.0"),
@@ -401,8 +422,11 @@ 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.*"),
                 ("2.0.post1", "!=2.0.post1.*"),