simplify extra markers 2 (#845)

Without this change the union of `extra == "a" and extra == "c"` and `extra == "a" or extra == "b"` is `extra == "a" and extra == "c" or extra == "a" or extra == "b"`. With the change, it is simplified to `extra == "a" or extra == "b"`.

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

@@ -165,8 +165,11 @@ def union(self, other: BaseConstraint) -> BaseConstraint:
 
         else:
             assert isinstance(other, MultiConstraint)
-            # (A or B) or (C and D) => nothing to do
+            # (A or B) or (A and D) => A or B
+            if any(c in other.constraints for c in self._constraints):
+                return self
 
+            # (A or B) or (C and D) => nothing to do
             new_constraints = [*self._constraints, other]
 
         if len(new_constraints) == 1:

tests/constraints/generic/test_constraint.py

@@ -1580,6 +1580,11 @@ def test_union(
                 ),
             ),
         ),
+        (
+            UnionConstraint(ExtraConstraint("extra1"), ExtraConstraint("extra2")),
+            ExtraMultiConstraint(ExtraConstraint("extra1"), ExtraConstraint("extra3")),
+            UnionConstraint(ExtraConstraint("extra1"), ExtraConstraint("extra2")),
+        ),
     ],
 )
 def test_union_extra(

tests/version/test_markers.py

@@ -668,6 +668,16 @@ def test_single_marker_union_with_inverse() -> None:
             'extra == "a" or extra == "c"',
             'extra != "a" and extra != "b" or extra == "a" or extra == "c"',
         ),
+        (
+            'extra == "a" or extra == "b"',
+            'extra == "a" and extra == "c"',
+            'extra == "a" or extra == "b"',
+        ),
+        (
+            'extra == "a" and extra == "c"',
+            'extra == "a" or extra == "b"',
+            'extra == "a" or extra == "b"',
+        ),
     ],
 )
 def test_single_marker_union_extras(marker1: str, marker2: str, expected: str) -> None: