markers: recognize empty python_version markers

Without this fix, the intersection of `python_version > "3.8"` and `python_version < "3.9"` is not detected as empty marker.

Author: radoering

src/poetry/core/version/markers.py

@@ -1231,12 +1231,20 @@ def _merge_single_markers(
     elif marker1.name == "python_version":
         from poetry.core.packages.utils.utils import get_python_constraint_from_marker
 
-        if isinstance(result_constraint, VersionRange) and result_constraint.min:
-            # Convert 'python_version >= "3.8" and python_version < "3.9"'
-            # to 'python_version == "3.8"'
-            candidate = parse_marker(f'{marker1.name} == "{result_constraint.min}"')
-            if get_python_constraint_from_marker(candidate) == result_constraint:
-                result_marker = candidate
+        if isinstance(result_constraint, VersionRange) and merge_class == MultiMarker:
+            if result_constraint.min:
+                # Convert 'python_version >= "3.8" and python_version < "3.9"'
+                # to 'python_version == "3.8"'.
+                candidate = parse_marker(f'{marker1.name} == "{result_constraint.min}"')
+                if get_python_constraint_from_marker(candidate) == result_constraint:
+                    result_marker = candidate
+            if result_marker is None:
+                # Detect 'python_version > "3.8" and python_version < "3.9"' as empty.
+                result_constraint = get_python_constraint_from_marker(
+                    marker1
+                ).intersect(get_python_constraint_from_marker(marker2))
+                if result_constraint.is_empty():
+                    result_marker = EmptyMarker()
 
         elif isinstance(result_constraint, VersionUnion) and merge_class == MarkerUnion:
             # Convert 'python_version == "3.8" or python_version >= "3.9"'

tests/version/test_markers.py

@@ -171,6 +171,22 @@ def test_single_marker_intersect() -> None:
     assert str(intersection) == 'python_version >= "3.4" and python_version < "3.6"'
 
 
+@pytest.mark.parametrize(
+    ("marker1", "marker2"),
+    [
+        ('sys_platform == "win32"', 'sys_platform == "linux"'),
+        ('sys_platform != "win32"', 'sys_platform == "win32"'),
+        ('python_version >= "3.6"', 'python_version < "3.6"'),
+        ('python_version == "3.6"', 'python_version == "3.7"'),
+        ('python_version > "3.6"', 'python_version <= "3.6"'),
+        ('python_version >= "3.6"', 'python_version < "3.6"'),
+        ('python_version > "3.6"', 'python_version < "3.7"'),
+    ],
+)
+def test_single_marker_intersect_is_empty(marker1: str, marker2: str) -> None:
+    assert parse_marker(marker1).intersect(parse_marker(marker2)).is_empty()
+
+
 @pytest.mark.parametrize(
     ("marker1", "marker2", "expected"),
     [
@@ -852,11 +868,6 @@ def test_multi_marker_union_multi_is_multi(
             'python_version >= "3.6" and python_version < "3.8"',
             'python_version >= "3.6" and python_version < "3.8"',
         ),
-        (
-            'python_version > "3.6" and python_full_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" and python_full_version < "3.7.2"',
             'python_version > "3.6" and python_version < "3.8"',
@@ -2260,16 +2271,16 @@ def test_intersection_no_endless_recursion() -> None:
         ' and extra != "postgis"'
     )
     m2 = parse_marker(
-        'python_version > "3.12" and python_version < "3.13" or extra != "databricks"'
+        'python_version >= "3.12" and python_version < "3.13" or extra != "databricks"'
     )
     expected = (
         '(python_version < "3.9" or extra != "bigquery" and extra != "parquet"'
         ' and extra != "motherduck" and extra != "athena" and extra != "synapse"'
         ' and extra != "clickhouse" and extra != "dremio" and extra != "lancedb"'
         ' and extra != "deltalake" and extra != "pyiceberg")'
         ' and python_version < "3.13" and extra != "postgres" and extra != "redshift"'
-        ' and extra != "postgis" and (python_version > "3.12"'
-        ' and python_version < "3.13" or extra != "databricks")'
+        ' and extra != "postgis"'
+        ' and (python_version == "3.12" or extra != "databricks")'
     )
     assert str(m1.intersect(m2)) == expected