Sema: Fix substMemberTypeWithBase() for non-generic typealias with 'where' clause

getContextSubstitutionMap() builds a substitution map for the generic signature of
the parent context, which is wrong if the typealias has its own 'where' clause.

Author: slavapestov

lib/Sema/TypeCheckType.cpp

@@ -4623,7 +4623,7 @@ Type TypeChecker::substMemberTypeWithBase(ModuleDecl *module,
 
   auto *aliasDecl = dyn_cast<TypeAliasDecl>(member);
   if (aliasDecl) {
-    if (aliasDecl->getGenericParams()) {
+    if (aliasDecl->isGeneric()) {
       return UnboundGenericType::get(
           aliasDecl, baseTy,
           aliasDecl->getASTContext());
@@ -4647,7 +4647,7 @@ Type TypeChecker::substMemberTypeWithBase(ModuleDecl *module,
     if (baseTy->is<ErrorType>())
       return ErrorType::get(memberType);
 
-    subs = baseTy->getContextSubstitutionMap(module, member->getDeclContext());
+    subs = baseTy->getMemberSubstitutionMap(module, member);
     resultType = memberType.subst(subs);
   } else {
     resultType = memberType;

test/Generics/where_clause_contextually_generic_decls.swift

@@ -127,6 +127,8 @@ struct Container<T> {
   // expected-error@-1 {{invalid redeclaration of 'NestedAlias}}
   typealias NestedAlias2 = T.Magnitude where T: FixedWidthInteger
 
+  typealias NestedAlias3 = T.Element where T: Sequence
+
   class NestedClass where T: Equatable {}
 }
 
@@ -154,3 +156,12 @@ _ = Container<Bool>.NestedClass.self
 _ = Container<String>.NestedStruct.self
 _ = Container<Array<UInt8>>.NestedStruct2.self
 _ = Container<Array<Double>>.NestedStruct2.NestedEnum.self
+
+// Make sure the substitution here actually succeeds instead of producing an ErrorType
+func sameType<T>(_: T.Type, _: T.Type) {}
+sameType(Container<Array<Int>>.NestedAlias3.self, Int.self)
+sameType(Container<Array<Bool>>.NestedAlias3.self, Int.self)
+// expected-error@-1 {{cannot convert value of type 'Int.Type' to expected argument type 'Container<Array<Bool>>.NestedAlias3.Type' (aka 'Bool.Type')}}
+
+sameType(Container<Array<Int>>.NestedAlias3.self, Bool.self)
+// expected-error@-1 {{cannot convert value of type 'Bool.Type' to expected argument type 'Container<Array<Int>>.NestedAlias3.Type' (aka 'Int.Type')}}

validation-test/compiler_crashers_2_fixed/0161-issue-49119.swift

@@ -8,8 +8,8 @@ protocol P {
 
 struct Type<Param> {}
 extension Type: P where Param: P, Param.A == Type<Param> {
-  // expected-error@-1 6{{extension of generic struct 'Type' has self-referential generic requirements}}
-  // expected-note@-2 6{{through reference here}}
+  // expected-error@-1 5{{extension of generic struct 'Type' has self-referential generic requirements}}
+  // expected-note@-2 5{{through reference here}}
   // expected-error@-3 {{type 'Type<Param>' does not conform to protocol 'P'}}
   typealias A = Param
   // expected-note@-1 2{{through reference here}}