feat(spec): Add support for directive

Author: cschiewek

lib/absinthe/schema/prototype/notation.ex

@@ -45,6 +45,19 @@ defmodule Absinthe.Schema.Prototype.Notation do
         on [:scalar]
       end
 
+      # https://spec.graphql.org/September2025/#sec--oneOf
+      directive :one_of do
+        description """
+        The @oneOf built-in directive is used within the type system definition language to indicate an Input Object is a OneOf Input Object.
+
+        A OneOf Input Object is a special variant of Input Object where exactly one field must be set and non-null, all others being omitted.
+        This is useful for representing situations where an input may be one of many different options.
+        """
+
+        repeatable false
+        on [:input_field_definition]
+      end
+
       def pipeline(pipeline) do
         pipeline
         |> Absinthe.Pipeline.without(Absinthe.Phase.Schema.Validation.QueryTypeMustBeObject)

test/absinthe/introspection_test.exs

@@ -62,6 +62,16 @@ defmodule Absinthe.IntrospectionTest do
                         "onFragment" => true,
                         "onOperation" => false
                       },
+                      %{
+                        "description" =>
+                          "The @oneOf built-in directive is used within the type system definition language to indicate an Input Object is a OneOf Input Object.\n\nA OneOf Input Object is a special variant of Input Object where exactly one field must be set and non-null, all others being omitted.\nThis is useful for representing situations where an input may be one of many different options.",
+                        "isRepeatable" => false,
+                        "locations" => ["INPUT_FIELD_DEFINITION"],
+                        "name" => "oneOf",
+                        "onField" => false,
+                        "onFragment" => false,
+                        "onOperation" => false
+                      },
                       %{
                         "description" =>
                           "Directs the executor to skip this field or fragment when the `if` argument is true.",