more marker simplifications

Author: dimbleby

src/poetry/core/version/markers.py

@@ -513,6 +513,9 @@ def union_simplify(self, other: BaseMarker) -> BaseMarker | None:
             ):
                 return other
 
+            if not any(isinstance(m, MarkerUnion) for m in new_markers):
+                return self.of(*new_markers)
+
         elif isinstance(other, MultiMarker):
             common_markers = [
                 marker for marker in self.markers if marker in other.markers
@@ -545,11 +548,14 @@ def union_simplify(self, other: BaseMarker) -> BaseMarker | None:
                 # 'python_version >= "3.6.2" and python_version < "3.7"' ->
                 #
                 # 'python_version >= "3.6" and python_version < "3.7"'.
-                conjunction = [
+                unions = [
                     m1.union(m2) for m2 in other_unique_markers for m1 in unique_markers
                 ]
-                if not any(isinstance(m, MarkerUnion) for m in conjunction):
-                    return self.of(*conjunction)
+                conjunction = self.of(*unions)
+                if not isinstance(conjunction, MultiMarker) or not any(
+                    isinstance(m, MarkerUnion) for m in conjunction.markers
+                ):
+                    return conjunction
 
         return None
 

tests/version/test_markers.py

@@ -535,6 +535,37 @@ def test_multi_marker_union_multi_is_multi(
             'python_version >= "3.6.2" and python_version <= "3.7"',
             'python_version <= "3.7" and python_version >= "3.6"',
         ),
+        # A range covers an exact marker.
+        (
+            'python_version >= "3.6" and python_version <= "3.7"',
+            'python_version == "3.6"',
+            'python_version >= "3.6" and python_version <= "3.7"',
+        ),
+        (
+            'python_version >= "3.6" and python_version <= "3.7"',
+            'python_version == "3.6" and implementation_name == "cpython"',
+            'python_version >= "3.6" and python_version <= "3.7"',
+        ),
+        (
+            'python_version >= "3.6" and python_version <= "3.7"',
+            'python_version == "3.6.2"',
+            'python_version >= "3.6" and python_version <= "3.7"',
+        ),
+        (
+            'python_version >= "3.6" and python_version <= "3.7"',
+            'python_version == "3.6.2" and implementation_name == "cpython"',
+            'python_version >= "3.6" and python_version <= "3.7"',
+        ),
+        (
+            'python_version >= "3.6" and python_version <= "3.7"',
+            'python_version == "3.7"',
+            'python_version >= "3.6" and python_version <= "3.7"',
+        ),
+        (
+            'python_version >= "3.6" and python_version <= "3.7"',
+            'python_version == "3.7" and implementation_name == "cpython"',
+            'python_version >= "3.6" and python_version <= "3.7"',
+        ),
     ],
 )
 def test_version_ranges_collapse_on_union(