[Index] Avoid forming relations to non-indexed decls

If we shouldn't index the related decl, don't record
it as a relation.

Author: hamishknight

lib/Index/Index.cpp

@@ -543,6 +543,10 @@ class IndexSwiftASTWalker : public SourceEntityWalker {
 
   bool addRelation(IndexSymbol &Info, SymbolRoleSet RelationRoles, Decl *D) {
     assert(D);
+    if (auto *VD = dyn_cast<ValueDecl>(D)) {
+      if (!shouldIndex(VD, /*IsRef*/ true))
+        return true;
+    }
     auto Match = std::find_if(Info.Relations.begin(), Info.Relations.end(),
                               [D](IndexRelation R) { return R.decl == D; });
     if (Match != Info.Relations.end()) {

test/Index/index_module_inheritance_access.swift

@@ -0,0 +1,15 @@
+// RUN: %empty-directory(%t)
+//
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/Mod.swiftmodule -module-name Mod %s
+// RUN: %target-swift-ide-test -print-indexed-symbols -module-to-print Mod -source-filename %s -I %t | %FileCheck %s
+
+public class C {
+  fileprivate func foo() {}
+}
+public class D: C {
+  public override func foo() {}
+}
+
+// Make sure we don't report the override of the private member in the base class.
+//CHECK:      instance-method/Swift | foo() | s:3Mod1DC3fooyyF | Def,Dyn,RelChild | rel: 1
+//CHECK-NEXT: RelChild | class/Swift | D | s:3Mod1DC