Introduce result visiting (#1718)

* introduce result visiting

This changes introduces a few generic functions for revisiting data, demonstrating use of some of them within the RenameTypes transform.

= visitData can be used to recursively visit an ExecutionResult (or any object)

it takes two functions, one executed when entering the object, one when leaving

= visitResult can be used to visit a result by with a resultVisitorMap and/or an errorVisitorMap

visitResult visits the result using the request, so it knows the object type for every object within the map, as long as the result includes __typename info when requesting abstract types, and also knows the field name for each aliased key within the object.

* it executes the correct visitor from each objectVisitorMap included within the resultVisitorMap depending on the object type and field name
* it executes object visitors on the object itself when entering and leaving the object using the values from the __enter and __leave dummy field names within the objectVisitorMap
* it executes any visitors for leaf types included within the resultVisitorMap to provide a simple mechanism of visiting all fields of a certain leaf type

errors can also be visited -- these are meant to provide opportunities for transforming a GraphQLError, including the path, and so, if an errorVisitorMap is included, error visitors from the map will be collected for each field found in the path of the original error.

* Add result transforming to bundled transformers

These transformers now can utilize the visitData method to recursively visit the result and modify it as necessary by checking the __typename value. State about fields can be saved within the transformation context.

Adds result wrapping capability to the following generic transformers

= TransformCompositeFields
= TransformInterfaceFields
= TransformObjectFields
= TransformRootFields
= ExtendSchema
= MapFields

Adds result visiting usage to the following transfromers
= WrapFields
= WrapType
= HoistField

packages/utils/src/Interfaces.ts

@@ -153,7 +153,8 @@ export interface Transform {
 
 export type FieldNodeMapper = (
   fieldNode: FieldNode,
-  fragments: Record<string, FragmentDefinitionNode>
+  fragments: Record<string, FragmentDefinitionNode>,
+  transformationContext: Record<string, any>
 ) => SelectionNode | Array<SelectionNode>;
 
 export type FieldNodeMappers = Record<string, Record<string, FieldNodeMapper>>;

packages/utils/src/index.ts

@@ -46,3 +46,4 @@ export * from './implementsAbstractType';
 export * from './errors';
 export * from './toConfig';
 export * from './observableToAsyncIterable';
+export * from './visitResult';