[Bug Reproduce] Can't use undefined as enum value

[IvanGoncharov]

Extracted from #1267

From #836 it looks like both undefined and NaN could be used as an enum values:

const TestEnum = new GraphQLEnumType({
  name: 'TestEnum',
  values: {
    UNDEFINED: { value: undefined },
    NAN: { value: NaN },
  },
});

And run this query:

{
  undefined: fieldWithEnumInput(input: UNDEFINED)
  NaN: fieldWithEnumInput(input: NAN)
}

It will result in:

{
  "data": {
    "undefined": null,
    "NaN": null
  },
  "errors": [
    {
      "message": "Argument \"input\" has invalid value UNDEFINED.",
      "path": [ "undefined" ]
    }
    {
      "message": "Argument \"input\" has invalid value NAN.",
      "path": [ "NaN" ]
    }
  ]
}

[mjmahone]

I'm not sure why, but this is now causing test failures. I might be able to dig in later today.

[IvanGoncharov]

@mjmahone Yes it known issue with valueFromAST since it uses undefined return to indicate errors.
Ideally, it should be designed similar to coerceValue:

graphql-js/src/utilities/coerceValue.js

Lines 26 to 45 in 43c0d46

	type CoercedValue = {|
	+errors: $ReadOnlyArray<GraphQLError> | void,
	+value: mixed,
	|};
	type Path = {| +prev: Path | void, +key: string | number |};
	/**
	* Coerces a JavaScript value given a GraphQL Type.
	*
	* Returns either a value which is valid for the provided type or a list of
	* encountered coercion errors.
	*
	*/
	export function coerceValue(
	value: mixed,
	type: GraphQLInputType,
	blameNode?: ASTNode,
	path?: Path,
	): CoercedValue {

Correctly handling undefined is minor use case for breaking change but it will also makes errors to contain explanation why certain literal value is invalid which is pretty important.

This PR is [Bug Reproduce] just to document failing use cases until it will be fixed.

[IvanGoncharov]

Resolved in #2148