[SILGen] fix key path setter access for @testable

emitKeyPathComponentForDecl was only checking if the setter was
accessible from the current module, not the current function.
This failed when accessing an internal setter from a module
imported for testing.

Author: NobodyNada

lib/SILGen/SILGen.cpp

@@ -1458,6 +1458,7 @@ void SILGenModule::tryEmitPropertyDescriptor(AbstractStorageDecl *decl) {
                                                baseOperand, needsGenericContext,
                                                subs, decl, {},
                                                baseTy->getCanonicalType(),
+                                               M.getSwiftModule(),
                                                /*property descriptor*/ true);
 
   (void)SILProperty::create(M, /*serialized*/ false, decl, component);

lib/SILGen/SILGen.h

@@ -342,6 +342,7 @@ class LLVM_LIBRARY_VISIBILITY SILGenModule : public ASTVisitor<SILGenModule> {
                               AbstractStorageDecl *storage,
                               ArrayRef<ProtocolConformanceRef> indexHashables,
                               CanType baseTy,
+                              DeclContext *useDC,
                               bool forPropertyDescriptor);
 
   /// Known functions for bridging.

lib/SILGen/SILGenExpr.cpp

@@ -3354,6 +3354,7 @@ SILGenModule::emitKeyPathComponentForDecl(SILLocation loc,
                                 AbstractStorageDecl *storage,
                                 ArrayRef<ProtocolConformanceRef> indexHashables,
                                 CanType baseTy,
+                                DeclContext *useDC,
                                 bool forPropertyDescriptor) {
   auto baseDecl = storage;
 
@@ -3423,8 +3424,8 @@ SILGenModule::emitKeyPathComponentForDecl(SILLocation loc,
     // supply the settability if needed. We only reference it here if the
     // setter is public.
     if (shouldUseExternalKeyPathComponent())
-      return storage->isSettable(M.getSwiftModule())
-        && storage->isSetterAccessibleFrom(M.getSwiftModule());
+      return storage->isSettable(useDC)
+        && storage->isSetterAccessibleFrom(useDC);
     return storage->isSettable(storage->getDeclContext());
   };
 
@@ -3578,6 +3579,7 @@ RValue RValueEmitter::visitKeyPathExpr(KeyPathExpr *E, SGFContext C) {
                             decl,
                             component.getSubscriptIndexHashableConformances(),
                             baseTy,
+                            SGF.FunctionDC,
                             /*for descriptor*/ false));
       baseTy = loweredComponents.back().getComponentType();
       if (kind == KeyPathExpr::Component::Kind::Property)