[LookupVisibleDecls] Use correct BaseTy to check the decls are applicable

'lookupTypeMembers()' accepts 'BaseTy' to check found value decls are
applicable to the type. When looking into super classes, it used to use
the interface type of the super class which was not good.

Instead, use the original "base type" consistently.

rdar://problem/69308207
https://bugs.swift.org/browse/SR-13574

Author: rintaro

lib/Sema/LookupVisibleDecls.cpp

@@ -693,11 +693,13 @@ static void lookupVisibleMemberDeclsImpl(
     }
   }
 
+  auto lookupTy = BaseTy;
+
   const auto synthesizeAndLookupTypeMembers = [&](NominalTypeDecl *NTD) {
     synthesizeMemberDeclsForLookup(NTD, CurrDC);
 
     // Look in for members of a nominal type.
-    lookupTypeMembers(BaseTy, BaseTy, Consumer, CurrDC, LS, Reason);
+    lookupTypeMembers(BaseTy, lookupTy, Consumer, CurrDC, LS, Reason);
   };
 
   llvm::SmallPtrSet<ClassDecl *, 8> Ancestors;
@@ -725,7 +727,7 @@ static void lookupVisibleMemberDeclsImpl(
     Ancestors.insert(CD);
 
     Reason = getReasonForSuper(Reason);
-    BaseTy = CD->getSuperclass();
+    lookupTy = CD->getSuperclass();
 
     LS = LS.withOnSuperclass();
     if (CD->inheritsSuperclassInitializers())
@@ -734,7 +736,7 @@ static void lookupVisibleMemberDeclsImpl(
 
   // Look into the inheritance chain.
   do {
-    const auto CurClass = BaseTy->getClassOrBoundGenericClass();
+    const auto CurClass = lookupTy->getClassOrBoundGenericClass();
 
     // FIXME: This path is no substitute for an actual circularity check.
     // The real fix is to check that the superclass doesn't introduce a
@@ -744,10 +746,10 @@ static void lookupVisibleMemberDeclsImpl(
 
     synthesizeAndLookupTypeMembers(CurClass);
 
-    BaseTy = CurClass->getSuperclass();
+    lookupTy = CurClass->getSuperclass();
     if (!CurClass->inheritsSuperclassInitializers())
       LS = LS.withoutInheritsSuperclassInitializers();
-  } while (BaseTy);
+  } while (lookupTy);
 }
 
 swift::DynamicLookupInfo::DynamicLookupInfo(

test/IDE/complete_sr13574.swift

@@ -0,0 +1,31 @@
+// RUN: %swift-ide-test -code-completion -source-filename %s -code-completion-token=OVERRIDE | %FileCheck %s --check-prefix=OVERRIDE
+// RUN: %swift-ide-test -code-completion -source-filename %s -code-completion-token=MEMBER | %FileCheck %s --check-prefix=MEMBER
+
+class Root {
+    func onRoot() {}
+}
+
+class Base<T: Hashable>: Root {
+    func onBase() -> T {}
+}
+
+class Derived<T: Hashable>: Base<T> {
+    func onDerived() {}
+
+    func #^OVERRIDE^#
+// OVERRIDE: Begin completions, 2 items
+// OVERRIDE-DAG: Decl[InstanceMethod]/Super/Erase[5]: override func onBase() -> T {|};
+// OVERRIDE-DAG: Decl[InstanceMethod]/Super/Erase[5]: override func onRoot() {|};
+// OVERRIDE-DAG: End completions
+
+}
+
+func testMember(val: Derived<Int>) {
+    val.#^MEMBER^#
+// MEMBER: Begin completions, 4 items
+// MEMBER-DAG: Keyword[self]/CurrNominal:          self[#Derived<Int>#]; name=self
+// MEMBER-DAG: Decl[InstanceMethod]/CurrNominal:   onDerived()[#Void#]; name=onDerived()
+// MEMBER-DAG: Decl[InstanceMethod]/Super:         onBase()[#Int#]; name=onBase()
+// MEMBER-DAG: Decl[InstanceMethod]/Super:         onRoot()[#Void#]; name=onRoot()
+// MEMBER: End completions
+}