Issue 23190. Type check with a function type alias is its usage.

pkg/analyzer/lib/src/generated/resolver.dart

Index: pkg/analyzer/lib/src/generated/resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/resolver.dart b/pkg/analyzer/lib/src/generated/resolver.dart
index d9cc380a9492ddd227d1dfcb808c1c684eea0a82..ad791347e13ef18510f3c6d09f0aece4314a823f 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -4566,14 +4566,14 @@ class GatherUsedLocalElementsVisitor extends RecursiveAstVisitor {
     }
     // ignore places where the element is not actually used
     if (node.parent is TypeName) {
-      AstNode parent2 = node.parent.parent;
-      if (parent2 is IsExpression) {
-        return;
-      }
-      // We need to instantiate/extend/implement a class to actually use it.
-      // OTOH, function type aliases are used to define closure structures.
-      if (parent2 is VariableDeclarationList && element is ClassElement) {
-        return;
+      if (element is ClassElement) {
+        AstNode parent2 = node.parent.parent;
+        if (parent2 is IsExpression) {
+          return;
+        }
+        if (parent2 is VariableDeclarationList) {
+          return;
+        }
       }
     }
     // OK