Single marker union simplifications

src/poetry/core/semver/empty_constraint.py

@@ -14,6 +14,9 @@ def is_empty(self) -> bool:
     def is_any(self) -> bool:
         return False
 
+    def is_simple(self) -> bool:
+        return True
+
     def allows(self, version: "Version") -> bool:
         return False
 

src/poetry/core/semver/version.py

@@ -78,6 +78,9 @@ def is_any(self) -> bool:
     def is_empty(self) -> bool:
         return False
 
+    def is_simple(self) -> bool:
+        return True
+
     def allows(self, version: "Version") -> bool:
         if version is None:
             return False

src/poetry/core/semver/version_constraint.py

@@ -15,6 +15,10 @@ def is_empty(self) -> bool:
     def is_any(self) -> bool:
         raise NotImplementedError()
 
+    @abstractmethod
+    def is_simple(self) -> bool:
+        raise NotImplementedError()
+
     @abstractmethod
     def allows(self, version: "Version") -> bool:
         raise NotImplementedError()

src/poetry/core/semver/version_range.py

@@ -64,6 +64,9 @@ def is_empty(self) -> bool:
     def is_any(self) -> bool:
         return self._min is None and self._max is None
 
+    def is_simple(self) -> bool:
+        return self._min is None or self._max is None
+
     def allows(self, other: "Version") -> bool:
         if self._min is not None:
             if other < self._min:

src/poetry/core/semver/version_union.py

@@ -80,6 +80,9 @@ def is_empty(self) -> bool:
     def is_any(self) -> bool:
         return False
 
+    def is_simple(self) -> bool:
+        return self.excludes_single_version()
+
     def allows(self, version: "Version") -> bool:
         return any([constraint.allows(version) for constraint in self._ranges])
 

src/poetry/core/version/markers.py

@@ -8,6 +8,7 @@
 from typing import Type
 from typing import Union
 
+from poetry.core.semver.version_constraint import VersionConstraint
 from poetry.core.version.grammars import GRAMMAR_PEP_508_MARKERS
 from poetry.core.version.parser import Parser
 
@@ -16,7 +17,6 @@
     from lark import Tree
 
     from poetry.core.packages.constraints import BaseConstraint
-    from poetry.core.semver.version_constraint import VersionConstraint
 
 
 class InvalidMarker(ValueError):
@@ -183,7 +183,7 @@ class SingleMarker(BaseMarker):
     }
 
     def __init__(
-        self, name: str, constraint: Union[str, "BaseConstraint", "VersionConstraint"]
+        self, name: str, constraint: Union[str, "BaseConstraint", VersionConstraint]
     ) -> None:
         from poetry.core.packages.constraints import (
             parse_constraint as parse_generic_constraint,
@@ -247,7 +247,7 @@ def constraint_string(self) -> str:
         return self._constraint_string
 
     @property
-    def constraint(self) -> Union["BaseConstraint", "VersionConstraint"]:
+    def constraint(self) -> Union["BaseConstraint", VersionConstraint]:
         return self._constraint
 
     @property
@@ -552,28 +552,30 @@ def of(cls, *markers: BaseMarker) -> BaseMarker:
             if marker in new_markers:
                 continue
 
-            if (
-                isinstance(marker, SingleMarker)
-                and marker.name in PYTHON_VERSION_MARKERS
-            ):
+            if isinstance(marker, SingleMarker):
                 included = False
                 for i, mark in enumerate(new_markers):
-                    if (
-                        not isinstance(mark, SingleMarker)
-                        or mark.name not in PYTHON_VERSION_MARKERS
+                    if isinstance(mark, SingleMarker) and (
+                        mark.name == marker.name
+                        or (
+                            mark.name in PYTHON_VERSION_MARKERS
+                            and marker.name in PYTHON_VERSION_MARKERS
+                        )
                     ):
-                        continue
-
-                    union = mark.constraint.union(marker.constraint)
-                    if union == mark.constraint:
-                        included = True
-                        break
-                    elif union == marker.constraint:
-                        new_markers[i] = marker
-                        included = True
-                        break
-                    elif union.is_any():
-                        return AnyMarker()
+                        union = mark.constraint.union(marker.constraint)
+                        if union == mark.constraint:
+                            included = True
+                            break
+                        elif union == marker.constraint:
+                            new_markers[i] = marker
+                            included = True
+                            break
+                        elif union.is_any():
+                            return AnyMarker()
+                        elif isinstance(union, VersionConstraint) and union.is_simple():
+                            new_markers[i] = SingleMarker(mark.name, union)
+                            included = True
+                            break
 
                 if included:
                     continue

tests/version/test_markers.py

@@ -173,17 +173,51 @@ def test_single_marker_union():
     union = m.union(parse_marker('implementation_name == "cpython"'))
     assert str(union) == 'sys_platform == "darwin" or implementation_name == "cpython"'
 
+
+def test_single_marker_union_is_any():
     m = parse_marker('python_version >= "3.4"')
 
     union = m.union(parse_marker('python_version < "3.6"'))
     assert union.is_any()
 
 
-def test_single_marker_union_compacts_constraints():
-    m = parse_marker('python_version < "3.6"')
+@pytest.mark.parametrize(
+    ("marker1", "marker2", "expected"),
+    [
+        (
+            'python_version < "3.6"',
+            'python_version < "3.4"',
+            'python_version < "3.6"',
+        ),
+        (
+            'sys_platform == "linux"',
+            'sys_platform != "win32"',
+            'sys_platform != "win32"',
+        ),
+        (
+            'python_version == "3.6"',
+            'python_version > "3.6"',
+            'python_version >= "3.6"',
+        ),
+        (
+            'python_version == "3.6"',
+            'python_version < "3.6"',
+            'python_version <= "3.6"',
+        ),
+        (
+            'python_version < "3.6"',
+            'python_version > "3.6"',
+            'python_version != "3.6"',
+        ),
+    ],
+)
+def test_single_marker_union_is_single_marker(
+    marker1: str, marker2: str, expected: str
+):
+    m = parse_marker(marker1)
 
-    union = m.union(parse_marker('python_version < "3.4"'))
-    assert str(union) == 'python_version < "3.6"'
+    union = m.union(parse_marker(marker2))
+    assert str(union) == expected
 
 
 def test_single_marker_union_with_multi():