Report unused function type aliases.

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 0d20c8b1c7b4dbb7081d8dcfc2cfcab0126cc129..9c12b2dd44d7fae34a272c75e58ca124b4584c9b 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -4568,7 +4568,9 @@ class GatherUsedLocalElementsVisitor extends RecursiveAstVisitor {
       if (parent2 is IsExpression) {
         return;
       }
-      if (parent2 is VariableDeclarationList) {
+      // 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;
       }
     }
@@ -14907,6 +14909,17 @@ class UnusedLocalElementsVerifier extends RecursiveElementVisitor {
   }
 
   @override
+  visitFunctionTypeAliasElement(FunctionTypeAliasElement element) {
+    if (!_isUsedElement(element)) {
+      _reportErrorForElement(HintCode.UNUSED_ELEMENT, element, [
+        element.kind.displayName,
+        element.displayName
+      ]);
+    }
+    super.visitFunctionTypeAliasElement(element);
+  }
+
+  @override
   visitLocalVariableElement(LocalVariableElement element) {
     if (!_isUsedElement(element) && !_isNamedUnderscore(element)) {
       HintCode errorCode;