1 files changed, 64 insertions, 0 deletions
diff --git a/app/graphql/types/global_id_type.rb b/app/graphql/types/global_id_type.rb
new file mode 100644
index 00000000000..a3964ba83e1
--- /dev/null
+++ b/app/graphql/types/global_id_type.rb
@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+
+module Types
+  class GlobalIDType < BaseScalar
+    graphql_name 'GlobalID'
+    description 'A global identifier'
+
+    # @param value [GID]
+    # @return [String]
+    def self.coerce_result(value, _ctx)
+      ::Gitlab::GlobalId.as_global_id(value).to_s
+    end
+
+    # @param value [String]
+    # @return [GID]
+    def self.coerce_input(value, _ctx)
+      gid = GlobalID.parse(value)
+      raise GraphQL::CoercionError, "#{value.inspect} is not a valid Global ID" if gid.nil?
+      raise GraphQL::CoercionError, "#{value.inspect} is not a Gitlab Global ID" unless gid.app == GlobalID.app
+
+      gid
+    end
+
+    # Construct a restricted type, that can only be inhabited by an ID of
+    # a given model class.
+    def self.[](model_class)
+      @id_types ||= {}
+
+      @id_types[model_class] ||= Class.new(self) do
+        graphql_name "#{model_class.name.gsub(/::/, '')}ID"
+        description "Identifier of #{model_class.name}"
+
+        self.define_singleton_method(:to_s) do
+          graphql_name
+        end
+
+        self.define_singleton_method(:inspect) do
+          graphql_name
+        end
+
+        self.define_singleton_method(:coerce_result) do |gid, ctx|
+          global_id = ::Gitlab::GlobalId.as_global_id(gid, model_name: model_class.name)
+
+          if suitable?(global_id)
+            global_id.to_s
+          else
+            raise GraphQL::CoercionError, "Expected a #{model_class.name} ID, got #{global_id}"
+          end
+        end
+
+        self.define_singleton_method(:suitable?) do |gid|
+          gid&.model_class&.ancestors&.include?(model_class)
+        end
+
+        self.define_singleton_method(:coerce_input) do |string, ctx|
+          gid = super(string, ctx)
+          raise GraphQL::CoercionError, "#{string.inspect} does not represent an instance of #{model_class.name}" unless suitable?(gid)
+
+          gid
+        end
+      end
+    end
+  end
+end