Explain why we don't need to pass dep.artifact()

Author: weihanglo

src/cargo/core/compiler/unit_dependencies.rs

@@ -1103,7 +1103,10 @@ impl<'a, 'cfg> State<'a, 'cfg> {
                         // If this is an optional dependency, and the new feature resolver
                         // did not enable it, don't include it.
                         if dep.is_optional() {
-                            let features_for = unit_for.map_to_features_for(None);
+                            // This `unit_for` is from parent dep and *SHOULD* contains its own
+                            // artifact dep infomration inside `artifact_target_for_features`.
+                            // So, no need to map any artifact info from an incorrect `dep.artifact()`.
+                            let features_for = unit_for.map_to_features_for(IS_NO_ARTIFACT_DEP);
                             if !self.is_dep_activated(pkg_id, features_for, dep.name_in_toml()) {
                                 return false;
                             }