Add an argument validation step

Author: rmosolgo

lib/graphql/schema.rb

@@ -1725,6 +1725,10 @@ def add_type_and_traverse(t, root:)
         }
 
         addition.directives.each { |dir_class| own_directives[dir_class.graphql_name] = dir_class }
+
+        addition.arguments_with_default_values.each do |arg|
+          arg.validate_default_value
+        end
       end
 
       def lazy_methods

lib/graphql/schema/addition.rb

@@ -3,7 +3,7 @@
 module GraphQL
   class Schema
     class Addition
-      attr_reader :directives, :possible_types, :types, :union_memberships, :references
+      attr_reader :directives, :possible_types, :types, :union_memberships, :references, :arguments_with_default_values
 
       def initialize(schema:, own_types:, new_types:)
         @schema = schema
@@ -13,6 +13,7 @@ def initialize(schema:, own_types:, new_types:)
         @types = {}
         @union_memberships = {}
         @references = Hash.new { |h, k| h[k] = [] }
+        @arguments_with_default_values = []
         add_type_and_traverse(new_types)
       end
 
@@ -164,6 +165,9 @@ def add_type(type, owner:, late_types:, path:)
             arg_type = arg.type.unwrap
             references_to(arg_type, from: arg)
             add_type(arg_type, owner: arg, late_types: late_types, path: path + [name])
+            if arg.default_value?
+              @arguments_with_default_values << arg
+            end
           end
         else
           @types[type.graphql_name] = type
@@ -180,6 +184,9 @@ def add_type(type, owner:, late_types:, path:)
                 arg_type = arg.type.unwrap
                 references_to(arg_type, from: arg)
                 add_type(arg_type, owner: arg, late_types: late_types, path: field_path + [arg_name])
+                if arg.default_value?
+                  @arguments_with_default_values << arg
+                end
               end
             end
           end
@@ -189,6 +196,9 @@ def add_type(type, owner:, late_types:, path:)
               arg_type = arg.type.unwrap
               references_to(arg_type, from: arg)
               add_type(arg_type, owner: arg, late_types: late_types, path: path + [arg_name])
+              if arg.default_value?
+                @arguments_with_default_values << arg
+              end
             end
           end
           if type.kind.union?

lib/graphql/schema/argument.rb

@@ -295,6 +295,22 @@ def coerce_into_values(parent_object, values, context, argument_values)
         end
       end
 
+      # @api private
+      def validate_default_value
+        coerced_default_value = type.coerce_isolated_result(default_value) unless default_value.nil?
+        res = type.valid_isolated_input?(coerced_default_value)
+        if !res
+          raise InvalidDefaultValueError.new(self)
+        end
+      end
+
+      class InvalidDefaultValueError < GraphQL::Error
+        def initialize(argument)
+          message = "`#{argument.path}` has an invalid default value: `#{argument.default_value.inspect}` isn't accepted by `#{argument.type.to_type_signature}`; update the default value or the argument type."
+          super(message)
+        end
+      end
+
       private
 
       def validate_input_type(input_type)

spec/graphql/schema/argument_spec.rb

@@ -396,4 +396,41 @@ class InvalidLazyArgumentObject < GraphQL::Schema::Object
       assert_equal expected_message, err.message
     end
   end
+
+  describe "validating default values" do
+    it "raises when field argument default values are invalid" do
+      query_type = Class.new(GraphQL::Schema::Object) do
+        graphql_name "Query"
+        field :f1, Integer, null: false do
+          argument :arg1, Integer, default_value: nil, required: true
+        end
+      end
+
+      err = assert_raises GraphQL::Schema::Argument::InvalidDefaultValueError do
+        Class.new(GraphQL::Schema) do
+          query(query_type)
+        end
+      end
+      expected_message = "`Query.f1.arg1` has an invalid default value: `nil` isn't accepted by `Int!`; update the default value or the argument type."
+      assert_equal expected_message, err.message
+    end
+
+    it "TODO: raises when input argument default values are invalid"
+
+    it "TODO: raises when directive argument default values are invalid"
+
+    it "raises when parsing a schema from a string" do
+      schema_str = <<-GRAPHQL
+      type Query {
+        f1(arg1: Int! = null): Int!
+      }
+      GRAPHQL
+
+      err = assert_raises GraphQL::Schema::Argument::InvalidDefaultValueError do
+        GraphQL::Schema.from_definition(schema_str)
+      end
+      expected_message = "`Query.f1.arg1` has an invalid default value: `nil` isn't accepted by `Int!`; update the default value or the argument type."
+      assert_equal expected_message, err.message
+    end
+  end
 end