[SILGen] Amend checks preventing metatype keypaths in SilGen.

Author: amritpan

lib/SILGen/SILGen.cpp

@@ -1856,9 +1856,10 @@ SILGenModule::canStorageUseStoredKeyPathComponent(AbstractStorageDecl *decl,
                                           expansion);
   switch (strategy.getKind()) {
   case AccessStrategy::Storage: {
-    // Keypaths rely on accessors to handle the special behavior of weak or
-    // unowned properties.
-    if (decl->getInterfaceType()->is<ReferenceStorageType>())
+    // Keypaths rely on accessors to handle the special behavior of weak,
+    // unowned, or static properties.
+    if (decl->getInterfaceType()->is<ReferenceStorageType>() ||
+        decl->isStatic())
       return false;
 
     // If the field offset depends on the generic instantiation, we have to
@@ -1956,10 +1957,7 @@ void SILGenModule::tryEmitPropertyDescriptor(AbstractStorageDecl *decl) {
 
   Type baseTy;
   if (decl->getDeclContext()->isTypeContext()) {
-    // TODO: Static properties should eventually be referenceable as
-    // keypaths from T.Type -> Element, viz `baseTy = MetatypeType::get(baseTy)`
-    assert(!decl->isStatic());
-    
+
     baseTy = decl->getDeclContext()->getSelfInterfaceType()
                  ->getReducedType(decl->getInnermostDeclContext()
                                       ->getGenericSignatureOfContext());

lib/SILGen/SILGenExpr.cpp

@@ -3164,6 +3164,11 @@ emitKeyPathRValueBase(SILGenFunction &subSGF,
   auto paramSubstValue = subSGF.emitOrigToSubstValue(loc, paramOrigValue,
                                              AbstractionPattern::getOpaque(),
                                              baseType);
+
+  // If base is a metatype, it cannot be opened as an existential or upcasted
+  // from a class.
+  if (baseType->is<MetatypeType>())
+    return paramSubstValue;
 
   // Pop open an existential container base.
   if (baseType->isAnyExistentialType()) {