RFC: Default value validation & coercion

Implements graphql/graphql-spec#793

* Adds validation of default values during schema validation.
* Adds coercion of default values anywhere a default value is used at runtime

Potentially breaking:
* Remove `astFromValue`
* Changes type of `defaultValue` provided during type configuration from an "internal" to an "external" value.

cspell.yml

@@ -27,6 +27,10 @@ ignoreRegExpList:
 
 words:
   - graphiql
+  - sublinks
+  - instanceof
+  - uncoerce
+  - uncoerced
 
   # Different names used inside tests
   - Skywalker

src/execution/__tests__/variables-test.ts

@@ -126,7 +126,6 @@ const TestType = new GraphQLObjectType({
     }),
     fieldWithNestedInputObject: fieldWithInputArg({
       type: TestNestedInputObject,
-      defaultValue: 'Hello World',
     }),
     list: fieldWithInputArg({ type: new GraphQLList(GraphQLString) }),
     nnList: fieldWithInputArg({

src/index.ts

@@ -440,8 +440,6 @@ export {
   typeFromAST,
   // Create a JavaScript value from a GraphQL language AST without a Type.
   valueFromASTUntyped,
-  // Create a GraphQL language AST from a JavaScript value.
-  astFromValue,
   // A helper to use within recursive-descent visitors which need to be aware of the GraphQL type system.
   TypeInfo,
   visitWithTypeInfo,

src/type/__tests__/enumType-test.ts

@@ -63,9 +63,7 @@ const QueryType = new GraphQLObjectType({
       args: {
         fromEnum: {
           type: ComplexEnum,
-          // Note: defaultValue is provided an *internal* representation for
-          // Enums, rather than the string name.
-          defaultValue: Complex1,
+          defaultValue: 'ONE',
         },
         provideGoodValue: { type: GraphQLBoolean },
         provideBadValue: { type: GraphQLBoolean },