Add unique field names validation

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+- Bug Fix: [Validate field names are unique to an object/interface/input object](https://github.com/absinthe-graphql/absinthe/pull/1135)
+
 ## 1.6.6
 
 - Feature: [Update telemetry dependency to stable ~> 1.0](https://github.com/absinthe-graphql/absinthe/pull/1097)

lib/absinthe/phase/schema/validation/unique_field_names.ex

@@ -0,0 +1,69 @@
+defmodule Absinthe.Phase.Schema.Validation.UniqueFieldNames do
+  @moduledoc false
+
+  @behaviour Absinthe.Phase
+  alias Absinthe.Blueprint
+
+  def run(bp, _) do
+    bp =
+      bp
+      |> Blueprint.prewalk(&handle_schemas(&1, :name))
+
+    {:ok, bp}
+  end
+
+  defp handle_schemas(%Blueprint.Schema.SchemaDefinition{} = schema, key) do
+    schema = Blueprint.prewalk(schema, &validate_types(&1, key))
+    {:halt, schema}
+  end
+
+  defp handle_schemas(obj, _) do
+    obj
+  end
+
+  defp validate_types(%type{} = object, key)
+       when type in [
+              Blueprint.Schema.InputObjectTypeDefinition,
+              Blueprint.Schema.InterfaceTypeDefinition,
+              Blueprint.Schema.ObjectTypeDefinition
+            ] do
+    fields =
+      for field <- object.fields do
+        name_counts = Enum.frequencies_by(object.fields, &Map.get(&1, key))
+
+        if duplicate?(name_counts, field, key) do
+          Absinthe.Phase.put_error(field, error(field, object))
+        else
+          field
+        end
+      end
+
+    %{object | fields: fields}
+  end
+
+  defp validate_types(type, _) do
+    type
+  end
+
+  defp duplicate?(name_counts, field, key) do
+    field_identifier = Map.get(field, key)
+    Map.get(name_counts, field_identifier, 0) > 1
+  end
+
+  defp error(field, object) do
+    %Absinthe.Phase.Error{
+      message: explanation(field, object),
+      locations: [field.__reference__.location],
+      phase: __MODULE__,
+      extra: field
+    }
+  end
+
+  def explanation(field, object) do
+    """
+    The field #{inspect(field.name)} is not unique in type #{inspect(object.name)}.
+
+    The field must have a unique name within that Object type; no two fields may share the same name.
+    """
+  end
+end

lib/absinthe/pipeline.ex

@@ -151,6 +151,7 @@ defmodule Absinthe.Pipeline do
       Phase.Schema.Validation.NoInterfaceCyles,
       Phase.Schema.Validation.QueryTypeMustBeObject,
       Phase.Schema.Validation.NamesMustBeValid,
+      Phase.Schema.Validation.UniqueFieldNames,
       Phase.Schema.RegisterTriggers,
       Phase.Schema.MarkReferenced,
       Phase.Schema.ReformatDescriptions,

test/absinthe/schema/rule/unique_field_names_test.exs

@@ -0,0 +1,75 @@
+defmodule Absinthe.Schema.Rule.UniqueFieldNamesTest do
+  use Absinthe.Case, async: true
+
+  @duplicate_object_fields ~S(
+  defmodule DuplicateObjectFields do
+    use Absinthe.Schema
+
+    query do
+    end
+
+    import_sdl """
+      type Dog {
+        name: String!
+        name: String
+      }
+    """
+  end
+  )
+
+  @duplicate_interface_fields ~S(
+  defmodule DuplicateInterfaceFields do
+    use Absinthe.Schema
+
+    query do
+    end
+
+    import_sdl """
+      interface Animal {
+        tail: Boolean
+        tail: Boolean
+      }
+    """
+  end
+  )
+
+  @duplicate_input_fields ~S(
+  defmodule DuplicateInputFields do
+    use Absinthe.Schema
+
+    query do
+    end
+
+    import_sdl """
+      input AnimalInput {
+        species: String!
+        species: String!
+      }
+    """
+  end
+  )
+
+  test "errors on non unique object field names" do
+    error = ~r/The field \"name\" is not unique in type \"Dog\"./
+
+    assert_raise(Absinthe.Schema.Error, error, fn ->
+      Code.eval_string(@duplicate_object_fields)
+    end)
+  end
+
+  test "errors on non unique interface field names" do
+    error = ~r/The field \"tail\" is not unique in type \"Animal\"./
+
+    assert_raise(Absinthe.Schema.Error, error, fn ->
+      Code.eval_string(@duplicate_interface_fields)
+    end)
+  end
+
+  test "errors on non unique input field names" do
+    error = ~r/The field \"species\" is not unique in type \"AnimalInput\"./
+
+    assert_raise(Absinthe.Schema.Error, error, fn ->
+      Code.eval_string(@duplicate_input_fields)
+    end)
+  end
+end