[Sema] Only emit warnings for implicit self use in getters

This fixes a pre-existing bug where implicit DeclRefExprs involving
*any* expression of the same type within a getter were flagged with
warnings, even if they were references to something other than "self".

Author: allevato

lib/Sema/MiscDiagnostics.cpp

@@ -1469,6 +1469,13 @@ static void diagRecursivePropertyAccess(TypeChecker &TC, const Expr *E,
                             const FuncDecl *Accessor)
       : TC(TC), Var(var), Accessor(Accessor) {}
 
+    /// Return true if this is an implicit reference to self.
+    static bool isImplicitSelfUse(Expr *E) {
+      auto *DRE = dyn_cast<DeclRefExpr>(E);
+      return DRE && DRE->isImplicit() && isa<VarDecl>(DRE->getDecl()) &&
+             cast<VarDecl>(DRE->getDecl())->isSelfParameter();
+    }
+
     std::pair<bool, Expr *> walkToExprPre(Expr *E) override {
       Expr *subExpr;
       bool isStore = false;
@@ -1529,7 +1536,7 @@ static void diagRecursivePropertyAccess(TypeChecker &TC, const Expr *E,
         // Find MemberRefExprs that have an implicit "self" base.
         if (MRE->getMember().getDecl() == Var &&
             isa<DeclRefExpr>(MRE->getBase()) &&
-            MRE->getBase()->isImplicit()) {
+            isImplicitSelfUse(MRE->getBase())) {
 
           if (MRE->getAccessSemantics() != AccessSemantics::DirectToStorage) {
             bool shouldDiagnose = false;