Improve error for false as type, fixes rmosolgo#1334

Author: rmosolgo

lib/graphql/schema/member/build_type.rb

@@ -42,7 +42,7 @@ def parse_type(type_expr, null:)
                 if maybe_type.respond_to?(:graphql_definition)
                   maybe_type
                 else
-                  raise "Unexpected class/module found for GraphQL type: #{type_expr} (must be type definition class/module)"
+                  raise ArgumentError, "Unexpected class/module found for GraphQL type: #{type_expr} (must be type definition class/module)"
                 end
               end
             end
@@ -72,6 +72,8 @@ def parse_type(type_expr, null:)
               # Eg `String` => GraphQL::STRING_TYPE
               parse_type(type_expr.name, null: true)
             end
+          when false
+            raise ArgumentError, "Received `false` instead of a type, maybe a `!` should be replaced with `null: true` (for fields) or `required: true` (for arguments)"
           end
 
           if return_type.nil?

spec/graphql/schema/field_spec.rb

@@ -174,6 +174,21 @@
 
       assert_includes err.message, "Thing.stuff"
     end
+
+    it "makes a suggestion when the type is false" do
+      thing = Class.new(GraphQL::Schema::Object) do
+        graphql_name "Thing"
+        # False might come from an invalid `!`
+        field :stuff, false, null: false
+      end
+
+      err = assert_raises ArgumentError do
+        thing.fields["stuff"].type
+      end
+
+      assert_includes err.message, "Thing.stuff"
+      assert_includes err.message, "Received `false` instead of a type, maybe a `!` should be replaced with `null: true` (for fields) or `required: true` (for arguments)"
+    end
   end
 
   describe "mutation" do