Sema: Change checkOverrideAccessControl() to not need a synthesized setter

We can compute the setter's AccessScope directly, without creating
it first.

Author: slavapestov

include/swift/AST/Decl.h

@@ -4647,6 +4647,10 @@ class AbstractStorageDecl : public ValueDecl {
 
   AccessLevel getSetterFormalAccess() const;
 
+  AccessScope
+  getSetterFormalAccessScope(const DeclContext *useDC = nullptr,
+                             bool treatUsableFromInlineAsPublic = false) const;
+
   void setSetterAccess(AccessLevel accessLevel) {
     assert(!Accessors.getInt().hasValue());
     overwriteSetterAccess(accessLevel);

lib/AST/Decl.cpp

@@ -4799,6 +4799,13 @@ AbstractStorageDecl::getSetterFormalAccess() const {
         AccessLevel::Private);
 }
 
+AccessScope
+AbstractStorageDecl::getSetterFormalAccessScope(const DeclContext *useDC,
+                                    bool treatUsableFromInlineAsPublic) const {
+  return getAccessScopeForFormalAccess(this, getSetterFormalAccess(), useDC,
+                                       treatUsableFromInlineAsPublic);
+}
+
 void AbstractStorageDecl::setComputedSetter(AccessorDecl *setter) {
   assert(getImplInfo().getReadImpl() == ReadImplKind::Get);
   assert(!getImplInfo().supportsMutation());

lib/Sema/TypeCheckDeclOverride.cpp

@@ -896,12 +896,8 @@ static void checkOverrideAccessControl(ValueDecl *baseDecl, ValueDecl *decl,
     if (!shouldDiagnose && baseDecl->isSettable(dc)){
       auto matchASD = cast<AbstractStorageDecl>(baseDecl);
       if (matchASD->isSetterAccessibleFrom(dc)) {
-        // Match sure we've created the setter.
-        if (!matchASD->getSetter())
-          addExpectedOpaqueAccessorsToStorage(matchASD);
-
-        auto matchSetterAccessScope = matchASD->getSetter()
-          ->getFormalAccessScope(dc);
+        auto matchSetterAccessScope =
+          matchASD->getSetterFormalAccessScope(dc);
         auto requiredSetterAccessScope =
           matchSetterAccessScope.intersectWith(classAccessScope);
         auto setterScopeDC = requiredSetterAccessScope->getDeclContext();