Sema: Fix type of MemberRefExpr for a VarDecl with DynamicSelfType

This fixes a regression from 33401ae.

Fixes <rdar://problem/69804933>.

Author: slavapestov

lib/Sema/CSApply.cpp

@@ -1258,7 +1258,7 @@ namespace {
       }
 
       // For properties, build member references.
-      if (isa<VarDecl>(member)) {
+      if (auto *varDecl = dyn_cast<VarDecl>(member)) {
         if (isUnboundInstanceMember) {
           assert(memberLocator.getBaseLocator() &&
                  cs.UnevaluatedRootExprs.count(
@@ -1271,17 +1271,22 @@ namespace {
           base->setImplicit();
         }
 
+        auto hasDynamicSelf =
+          varDecl->getValueInterfaceType()->hasDynamicSelfType();
+
         auto memberRefExpr
           = new (context) MemberRefExpr(base, dotLoc, memberRef,
                                         memberLoc, Implicit, semantics);
         memberRefExpr->setIsSuper(isSuper);
+
+        if (hasDynamicSelf)
+          refTy = refTy->replaceCovariantResultType(containerTy, 1);
         cs.setType(memberRefExpr, refTy->castTo<FunctionType>()->getResult());
 
         Expr *result = memberRefExpr;
         closeExistential(result, locator);
 
-        if (cast<VarDecl>(member)->getValueInterfaceType()
-                                 ->hasDynamicSelfType()) {
+        if (hasDynamicSelf) {
           if (!baseTy->isEqual(containerTy)) {
             result = new (context) CovariantReturnConversionExpr(
                 result, simplifyType(openedType));

test/type/self.swift

@@ -299,3 +299,18 @@ struct OuterType {
     return optional.map { `Self`(string: $0) }
   }
 }
+
+// rdar://69804933 - CSApply assigns wrong type to MemberRefExpr for property with
+// DynamicSelfType
+class HasDynamicSelfProperty {
+  var me: Self {
+    return self
+  }
+}
+
+// SILGen doesn't care about the MemberRefExpr's type, so it's hard to come up with an
+// example that actually fails. Here, the rogue 'Self' type was diagnosed as being invalid
+// in a stored property initializer.
+class UsesDynamicSelfProperty {
+  var c = HasDynamicSelfProperty().me
+}