make constraints hashable

src/poetry/core/packages/constraints/any_constraint.py

@@ -37,3 +37,6 @@ def __str__(self) -> str:
 
     def __eq__(self, other: object) -> bool:
         return isinstance(other, BaseConstraint) and other.is_any()
+
+    def __hash__(self) -> int:
+        return hash("any")

src/poetry/core/packages/constraints/base_constraint.py

@@ -29,5 +29,8 @@ def is_empty(self) -> bool:
     def __repr__(self) -> str:
         return f"<{self.__class__.__name__} {str(self)}>"
 
+    def __hash__(self) -> int:
+        raise NotImplementedError()
+
     def __eq__(self, other: object) -> bool:
         raise NotImplementedError()

src/poetry/core/packages/constraints/empty_constraint.py

@@ -33,5 +33,8 @@ def __eq__(self, other: object) -> bool:
 
         return other.is_empty()
 
+    def __hash__(self) -> int:
+        return hash("empty")
+
     def __str__(self) -> str:
         return ""

src/poetry/core/packages/constraints/multi_constraint.py

@@ -81,6 +81,13 @@ def __eq__(self, other: object) -> bool:
 
         return set(self._constraints) == set(other._constraints)
 
+    def __hash__(self) -> int:
+        h = hash("multi")
+        for constraint in self._constraints:
+            h ^= hash(constraint)
+
+        return h
+
     def __str__(self) -> str:
         constraints = []
         for constraint in self._constraints:

src/poetry/core/packages/constraints/union_constraint.py

@@ -133,6 +133,13 @@ def __eq__(self, other: object) -> bool:
 
         return set(self._constraints) == set(other._constraints)
 
+    def __hash__(self) -> int:
+        h = hash("union")
+        for constraint in self._constraints:
+            h ^= hash(constraint)
+
+        return h
+
     def __str__(self) -> str:
         constraints = []
         for constraint in self._constraints:

tests/packages/constraints/test_constraint.py

@@ -167,3 +167,21 @@ def test_difference() -> None:
 
     assert c.difference(Constraint("win32")).is_empty()
     assert c.difference(Constraint("linux")) == c
+
+
+@pytest.mark.parametrize(
+    "constraint",
+    [
+        (EmptyConstraint()),
+        (AnyConstraint()),
+        (Constraint("win32")),
+        (UnionConstraint(Constraint("win32"), Constraint("linux"))),
+        (MultiConstraint(Constraint("win32", "!="), Constraint("linux", "!="))),
+    ],
+)
+def test_constraints_are_hashable(
+    constraint: BaseConstraint,
+) -> None:
+    # We're just testing that constraints are hashable, there's nothing much to say
+    # about the result.
+    hash(constraint)