Validate that deprecated requirements aren't required

lib/graphql/schema/argument.rb

@@ -61,7 +61,7 @@ def initialize(arg_name = nil, type_expr = nil, desc = nil, required:, type: nil
         @ast_node = ast_node
         @from_resolver = from_resolver
         @method_access = method_access
-        @deprecation_reason = deprecation_reason
+        self.deprecation_reason = deprecation_reason
 
         if definition_block
           if definition_block.arity == 1
@@ -91,17 +91,18 @@ def description(text = nil)
         end
       end
 
-      attr_writer :deprecation_reason
-
       # @return [String] Deprecation reason for this argument
       def deprecation_reason(text = nil)
         if text
+          validate_deprecated_or_optional(null: @null, deprecation_reason: text)
           @deprecation_reason = text
         else
           @deprecation_reason
         end
       end
 
+      alias_method :deprecation_reason=, :deprecation_reason
+
       def visible?(context)
         true
       end
@@ -164,6 +165,11 @@ def to_graphql
 
       def type=(new_type)
         validate_input_type(new_type)
+        # This isn't true for LateBoundTypes, but we can assume those will
+        # be updated via this codepath later in schema setup.
+        if new_type.respond_to?(:non_null?)
+          validate_deprecated_or_optional(null: !new_type.non_null?, deprecation_reason: deprecation_reason)
+        end
         @type = new_type
       end
 
@@ -174,8 +180,8 @@ def type
           rescue StandardError => err
             raise ArgumentError, "Couldn't build type for Argument #{@owner.name}.#{name}: #{err.class.name}: #{err.message}", err.backtrace
           end
-          validate_input_type(parsed_type)
-          parsed_type
+          # Use the setter method to get validations
+          self.type = parsed_type
         end
       end
 
@@ -212,6 +218,8 @@ def prepare_value(obj, value, context: nil)
         end
       end
 
+      private
+
       def validate_input_type(input_type)
         if input_type.is_a?(String) || input_type.is_a?(GraphQL::Schema::LateBoundType)
           # Do nothing; assume this will be validated later
@@ -223,6 +231,12 @@ def validate_input_type(input_type)
           # It's an input type, we're OK
         end
       end
+
+      def validate_deprecated_or_optional(null:, deprecation_reason:)
+        if deprecation_reason && !null
+          raise ArgumentError, "Required arguments cannot be deprecated: #{path}."
+        end
+      end
     end
   end
 end

spec/graphql/schema/argument_spec.rb

@@ -270,6 +270,8 @@ def self.object_from_id(id, ctx)
 
   describe "deprecation_reason:" do
     let(:arg) { SchemaArgumentTest::Query.fields["field"].arguments["arg"] }
+    let(:required_arg) {  SchemaArgumentTest::Query.fields["field"].arguments["requiredWithDefaultArg"] }
+
     it "sets deprecation reason" do
       arg.deprecation_reason "new deprecation reason"
       assert_equal "new deprecation reason", arg.deprecation_reason
@@ -283,6 +285,50 @@ def self.object_from_id(id, ctx)
       arg.deprecation_reason = "another new deprecation reason"
       assert_equal "another new deprecation reason", arg.deprecation_reason
     end
+
+    it "disallows deprecating required arguments in the constructor" do
+      err = assert_raises ArgumentError do
+        Class.new(GraphQL::Schema::InputObject) do
+          graphql_name 'MyInput'
+          argument :foo, String, required: true, deprecation_reason: "Don't use me"
+        end
+      end
+      assert_equal "Required arguments cannot be deprecated: MyInput.foo.", err.message
+    end
+
+    it "disallows deprecating required arguments in deprecation_reason=" do
+      assert_raises ArgumentError do
+        required_arg.deprecation_reason = "Don't use me"
+      end
+    end
+
+    it "disallows deprecating required arguments in deprecation_reason" do
+      assert_raises ArgumentError do
+        required_arg.deprecation_reason("Don't use me")
+      end
+    end
+
+    it "disallows deprecated required arguments whose type is a string" do
+      input_obj = Class.new(GraphQL::Schema::InputObject) do
+        graphql_name 'MyInput2'
+        argument :foo, "String!", required: false, deprecation_reason: "Don't use me"
+      end
+
+      query_type = Class.new(GraphQL::Schema::Object) do
+        graphql_name "Query"
+        field :f, String, null: true do
+          argument :arg, input_obj, required: false
+        end
+      end
+
+      err = assert_raises ArgumentError do
+        Class.new(GraphQL::Schema) do
+          query(query_type)
+        end
+      end
+
+      assert_equal "Required arguments cannot be deprecated: MyInput2.foo.", err.message
+    end
   end
 
   describe "invalid input types" do