adding support for the id scalar constrained as a string

lib/type-utils.js

@@ -4,13 +4,14 @@ const {
   GraphQLString,
   isNonNullType,
   isScalarType,
-  isListType
+  isListType,
+  GraphQLID
 } = require('graphql')
 const { ConstraintStringType, validate: validateStringFn } = require('../scalars/string')
 const { ConstraintNumberType, validate: validateNumberFn } = require('../scalars/number')
 
 function getConstraintTypeObject (fieldName, type, uniqueTypeName, directiveArgumentMap) {
-  if (type === GraphQLString) {
+  if (type === GraphQLString || type === GraphQLID) {
     return new ConstraintStringType(
       fieldName,
       uniqueTypeName,
@@ -30,7 +31,7 @@ function getConstraintTypeObject (fieldName, type, uniqueTypeName, directiveArgu
 }
 
 function getConstraintValidateFn (type) {
-  if (type === GraphQLString) {
+  if (type === GraphQLString || type === GraphQLID) {
     return validateStringFn
   } else if (type === GraphQLFloat || type === GraphQLInt) {
     return validateNumberFn

test/id.test.js

@@ -0,0 +1,64 @@
+const { deepStrictEqual, strictEqual } = require('assert')
+const { valueByImplType, isStatusCodeError } = require('./testutils')
+
+module.exports.test = function (setup, implType) {
+  describe('@constraint ID in INPUT_FIELD_DEFINITION treated like String', function () {
+    const query = `mutation createBook($input: BookInput) {
+      createBook(input: $input) {
+        title
+      }
+    }`
+
+    describe('#minLength', function () {
+      before(async function () {
+        this.typeDefs = `
+      type Query {
+        books: [Book]
+      }
+      type Book {
+        title: ID
+      }
+      type Mutation {
+        createBook(input: BookInput): Book
+      }
+      input BookInput {
+        title: ID! @constraint(minLength: 3)
+      }`
+
+        this.request = await setup({ typeDefs: this.typeDefs })
+      })
+
+      it('should pass', async function () {
+        const { body, statusCode } = await this.request
+          .post('/graphql')
+          .set('Accept', 'application/json')
+          .send({ query, variables: { input: { title: 'he💩' } } })
+
+        strictEqual(statusCode, 200)
+        deepStrictEqual(body, { data: { createBook: null } })
+      })
+
+      it('should fail', async function () {
+        const { body, statusCode } = await this.request
+          .post('/graphql')
+          .set('Accept', 'application/json')
+          .send({ query, variables: { input: { title: 'a💩' } } })
+
+        isStatusCodeError(statusCode, implType)
+        strictEqual(body.errors[0].message,
+          'Variable "$input" got invalid value "a💩" at "input.title"' + valueByImplType(implType, '; Expected type "title_String_NotNull_minLength_3"') + '. Must be at least 3 characters in length')
+      })
+
+      it('should fail with empty id', async function () {
+        const { body, statusCode } = await this.request
+          .post('/graphql')
+          .set('Accept', 'application/json')
+          .send({ query, variables: { input: { title: '' } } })
+
+        isStatusCodeError(statusCode, implType)
+        strictEqual(body.errors[0].message,
+          'Variable "$input" got invalid value "" at "input.title"' + valueByImplType(implType, '; Expected type "title_String_NotNull_minLength_3"') + '. Must be at least 3 characters in length')
+      })
+    })
+  })
+}