Add variant_label environment marker (#120)

Signed-off-by: Michał Górny <mgorny@quansight.com>

Author: mgorny

tests/test_api.py

@@ -531,7 +531,8 @@ def test_check_variant_supported_generic() -> None:
     )
 
 
-def test_get_variant_environment_dict() -> None:
+@pytest.mark.parametrize("label", [None, "foo"])
+def test_get_variant_environment_dict(label: str | None) -> None:
     vdesc = VariantDescription(
         [
             VariantProperty("ns1", "feat1", "val1"),
@@ -540,7 +541,7 @@ def test_get_variant_environment_dict() -> None:
             VariantProperty("ns3", "feat2", "val2"),
         ]
     )
-    assert get_variant_environment_dict(vdesc) == {
+    expected: dict[str, set[str] | str] = {
         "variant_features": {
             "ns1 :: feat1",
             "ns1 :: feat2",
@@ -559,6 +560,9 @@ def test_get_variant_environment_dict() -> None:
             "ns3 :: feat2 :: val2",
         },
     }
+    if label is not None:
+        expected["variant_label"] = label
+    assert get_variant_environment_dict(vdesc, label) == expected
 
 
 def test_make_variant_dist_info_invalid_label():

variantlib/api.py

@@ -324,16 +324,20 @@ def check_variant_supported(
 
 def get_variant_environment_dict(
     variant_desc: VariantDescription,
-) -> dict[str, set[str]]:
+    variant_label: str | None = None,
+) -> dict[str, set[str] | str]:
     """Get the dict for packaging Marker.evaluate()"""
 
-    return {
+    ret: dict[str, set[str] | str] = {
         "variant_namespaces": {vprop.namespace for vprop in variant_desc.properties},
         "variant_features": {
             vprop.feature_object.to_str() for vprop in variant_desc.properties
         },
         "variant_properties": {vprop.to_str() for vprop in variant_desc.properties},
     }
+    if variant_label is not None:
+        ret["variant_label"] = variant_label
+    return ret
 
 
 def get_variant_label(