Sema: Fix findDeclContextForType() for types nested inside closures

Fixes <rdar://problem/31803589>.

Author: slavapestov

lib/Sema/TypeCheckType.cpp

@@ -259,33 +259,22 @@ findDeclContextForType(TypeChecker &TC,
 
   auto ownerDC = typeDecl->getDeclContext();
 
-  // If the type is declared at the top level, there's nothing we can learn from
-  // walking our parent contexts.
-  if (ownerDC->isModuleScopeContext())
+  // If the type is not nested in another type, there's nothing we can
+  // learn from walking parent contexts.
+  if (!ownerDC->isTypeContext() ||
+      isa<GenericTypeParamDecl>(typeDecl))
     return std::make_tuple(Type(), true);
 
-  // Workaround for issue where generic typealias generic parameters are
-  // looked up with the wrong 'fromDC'.
-  if (isa<TypeAliasDecl>(ownerDC)) {
-    assert(isa<GenericTypeParamDecl>(typeDecl));
-    return std::make_tuple(Type(), true);
-  }
-
-  bool needsBaseType = (ownerDC->isTypeContext() &&
-                        !isa<GenericTypeParamDecl>(typeDecl));
   NominalTypeDecl *ownerNominal =
       ownerDC->getAsNominalTypeOrNominalTypeExtensionContext();
 
   // We might have an invalid extension that didn't resolve.
   //
   // FIXME: How did UnqualifiedLookup find the decl then?
-  if (needsBaseType && ownerNominal == nullptr)
+  if (ownerNominal == nullptr)
     return std::make_tuple(Type(), false);
 
   auto getSelfType = [&](DeclContext *DC) -> Type {
-    if (!needsBaseType)
-      return Type();
-
     // When looking up a nominal type declaration inside of a
     // protocol extension, always use the nominal type and
     // not the protocol 'Self' type.
@@ -332,13 +321,6 @@ findDeclContextForType(TypeChecker &TC,
     // We're going to check the next parent context.
   }
 
-  // If we didn't find the member in an immediate parent context and
-  // there is no base type, something went wrong.
-  if (!needsBaseType) {
-    assert(false && "Should have found non-type context by now");
-    return std::make_tuple(Type(), false);
-  }
-
   // Now, search the supertypes or refined protocols of each parent
   // context.
   for (auto parentDC = fromDC; !parentDC->isModuleContext();

test/decl/nested/type_in_function.swift

@@ -3,6 +3,23 @@
 // Generic class locally defined in non-generic function (rdar://problem/20116710)
 func f3() {
   class B<T> {}
+
+  class C : B<Int> {}
+
+  _ = B<Int>()
+  _ = C()
+}
+
+// Type defined inside a closure (rdar://problem/31803589)
+func hasAClosure() {
+  _ = {
+    enum E<T> { case a(T) }
+
+    let _ = E.a("hi")
+    let _ = E<String>.a("hi")
+    let _: E = .a("hi")
+    let _: E<String> = .a("hi")
+  }
 }
 
 protocol Racoon {