factory: respect python/platform constraints

This change ensures that when markers are specified, explicit python 
and platform constraints are not ignored.

src/poetry/core/factory.py

@@ -21,7 +21,6 @@
     from poetry.core.packages.types import DependencyTypes
     from poetry.core.poetry import Poetry
     from poetry.core.spdx.license import License
-    from poetry.core.version.markers import BaseMarker
 
     DependencyConstraint = Union[str, Dict[str, Any]]
     DependencyConfig = Mapping[
@@ -339,27 +338,25 @@ def create_dependency(
                     extras=constraint.get("extras", []),
                 )
 
-            if not markers:
-                marker: BaseMarker = AnyMarker()
-                if python_versions:
-                    marker = marker.intersect(
-                        parse_marker(
-                            create_nested_marker(
-                                "python_version", parse_constraint(python_versions)
-                            )
+            marker = parse_marker(markers) if markers else AnyMarker()
+
+            if python_versions:
+                marker = marker.intersect(
+                    parse_marker(
+                        create_nested_marker(
+                            "python_version", parse_constraint(python_versions)
                         )
                     )
+                )
 
-                if platform:
-                    marker = marker.intersect(
-                        parse_marker(
-                            create_nested_marker(
-                                "sys_platform", parse_generic_constraint(platform)
-                            )
+            if platform:
+                marker = marker.intersect(
+                    parse_marker(
+                        create_nested_marker(
+                            "sys_platform", parse_generic_constraint(platform)
                         )
                     )
-            else:
-                marker = parse_marker(markers)
+                )
 
             if not marker.is_any():
                 dependency.marker = marker

tests/test_factory.py

@@ -1,13 +1,19 @@
 from __future__ import annotations
 
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import pytest
 
 from poetry.core.factory import Factory
+from poetry.core.semver.helpers import parse_constraint
 from poetry.core.toml import TOMLFile
 
 
+if TYPE_CHECKING:
+    from poetry.core.factory import DependencyConstraint
+    from poetry.core.version.markers import BaseMarker
+
 fixtures_dir = Path(__file__).parent / "fixtures"
 
 
@@ -261,3 +267,56 @@ def test_create_poetry_with_groups_and_explicit_main():
     assert {dependency.name for dependency in dependencies} == {
         "aiohttp",
     }
+
+
+@pytest.mark.parametrize(
+    "constraint, exp_python, exp_marker",
+    [
+        ({"python": "3.7"}, "~3.7", 'python_version == "3.7"'),
+        ({"platform": "linux"}, "*", 'sys_platform == "linux"'),
+        ({"markers": 'python_version == "3.7"'}, "~3.7", 'python_version == "3.7"'),
+        (
+            {"markers": 'platform_machine == "x86_64"'},
+            "*",
+            'platform_machine == "x86_64"',
+        ),
+        (
+            {"python": "3.7", "markers": 'platform_machine == "x86_64"'},
+            "~3.7",
+            'platform_machine == "x86_64" and python_version == "3.7"',
+        ),
+        (
+            {"platform": "linux", "markers": 'platform_machine == "x86_64"'},
+            "*",
+            'platform_machine == "x86_64" and sys_platform == "linux"',
+        ),
+        (
+            {
+                "python": "3.7",
+                "platform": "linux",
+                "markers": 'platform_machine == "x86_64"',
+            },
+            "~3.7",
+            'platform_machine == "x86_64" and python_version == "3.7" and sys_platform'
+            ' == "linux"',
+        ),
+        (
+            {"python": ">=3.7", "markers": 'python_version < "4.0"'},
+            "<4.0 >=3.7",
+            'python_version < "4.0" and python_version >= "3.7"',
+        ),
+        (
+            {"platform": "linux", "markers": 'sys_platform == "win32"'},
+            "*",
+            "<empty>",
+        ),
+    ],
+)
+def test_create_dependency_marker_variants(
+    constraint: DependencyConstraint, exp_python: str, exp_marker: BaseMarker
+):
+    constraint["version"] = "1.0.0"
+    dep = Factory.create_dependency("foo", constraint)
+    assert dep.python_versions == exp_python
+    assert dep.python_constraint == parse_constraint(exp_python)
+    assert str(dep.marker) == exp_marker