Fix a version comparison of public version with local version zero (#920)

Author: dimbleby

src/poetry/core/version/pep440/version.py

@@ -26,12 +26,24 @@ class AlwaysSmaller:
     def __lt__(self, other: object) -> bool:
         return True
 
+    def __eq__(self, other: object) -> bool:
+        return isinstance(other, AlwaysSmaller)
+
+    def __hash__(self) -> int:
+        return id(AlwaysSmaller)
+
 
 @functools.total_ordering
 class AlwaysGreater:
     def __gt__(self, other: object) -> bool:
         return True
 
+    def __eq__(self, other: object) -> bool:
+        return isinstance(other, AlwaysGreater)
+
+    def __hash__(self) -> int:
+        return id(AlwaysGreater)
+
 
 class Infinity(AlwaysGreater, int):
     pass

tests/version/pep440/test_version.py

@@ -528,3 +528,16 @@ def test_without_postrelease(version: str, expected: str) -> None:
 def test_without_devrelease(version: str, expected: str) -> None:
     v = PEP440Version.parse(version)
     assert v.without_devrelease().text == expected
+
+
+def test_local_version_ordering_and_equality() -> None:
+    """PEP 440: versions with a local segment must sort after the same
+    version without one, and they must not compare equal.
+    """
+    v_plain = PEP440Version.parse("1.0")
+    v_local = PEP440Version.parse("1.0+0")
+
+    # 1.0+0 must be greater than 1.0 (local versions sort after)
+    assert v_local > v_plain
+    # They must not be equal
+    assert v_plain != v_local