[WIP] Nonnull operator

.vscode/launch.json

@@ -0,0 +1,16 @@
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "type": "node",
+      "request": "launch",
+      "name": "Mocha Tests",
+      "program": "${workspaceFolder}/node_modules/mocha/bin/_mocha",
+      "args": [
+        "src/validation/__tests__/OverlappingFieldsCanBeMergedRule-test.ts"
+      ],
+      "internalConsoleOptions": "openOnSessionStart",
+      "skipFiles": ["<node_internals>/**"]
+    }
+  ]
+}

src/__testUtils__/kitchenSinkQuery.ts

@@ -10,6 +10,10 @@ query queryName($foo: ComplexType, $site: Site = MOBILE) @onQuery {
           ...frag @onFragmentSpread
         }
       }
+      field3!
+      requiredField4: field4!
+      field5?
+      optionalField6: field6?
     }
     ... @skip(unless: $foo) {
       id

src/execution/execute.ts

@@ -39,6 +39,7 @@ import type {
   GraphQLResolveInfo,
   GraphQLTypeResolver,
   GraphQLList,
+  getNullableType,
 } from '../type/definition';
 import { assertValidSchema } from '../type/validate';
 import {
@@ -51,6 +52,7 @@ import {
   GraphQLSkipDirective,
 } from '../type/directives';
 import {
+  GraphQLNonNull,
   isObjectType,
   isAbstractType,
   isLeafType,
@@ -66,6 +68,7 @@ import {
   getArgumentValues,
   getDirectiveValues,
 } from './values';
+import { modifiedOutputType } from '../utilities/applyRequiredStatus';
 
 /**
  * Terminology
@@ -600,7 +603,8 @@ function resolveField(
     return;
   }
 
-  const returnType = fieldDef.type;
+  const returnType = modifiedOutputType(fieldDef.type, fieldNodes[0].required)
+
   const resolveFn = fieldDef.resolve ?? exeContext.fieldResolver;
 
   const info = buildResolveInfo(

src/index.ts

@@ -221,6 +221,7 @@ export {
   isTypeDefinitionNode,
   isTypeSystemExtensionNode,
   isTypeExtensionNode,
+  RequiredStatus,
 } from './language/index';
 
 export type {
@@ -436,6 +437,7 @@ export {
   DangerousChangeType,
   findBreakingChanges,
   findDangerousChanges,
+  modifiedOutputType,
 } from './utilities/index';
 
 export type {

src/language/__tests__/lexer-test.ts

@@ -162,16 +162,16 @@ describe('Lexer', () => {
   it('errors respect whitespace', () => {
     let caughtError;
     try {
-      lexOne(['', '', '    ?', ''].join('\n'));
+      lexOne(['', '', '    ~', ''].join('\n'));
     } catch (error) {
       caughtError = error;
     }
     expect(String(caughtError)).to.equal(dedent`
-      Syntax Error: Cannot parse the unexpected character "?".
+      Syntax Error: Cannot parse the unexpected character "~".
 
       GraphQL request:3:5
       2 |
-      3 |     ?
+      3 |     ~
         |     ^
       4 |
     `);
@@ -180,18 +180,18 @@ describe('Lexer', () => {
   it('updates line numbers in error for file context', () => {
     let caughtError;
     try {
-      const str = ['', '', '     ?', ''].join('\n');
+      const str = ['', '', '     ~', ''].join('\n');
       const source = new Source(str, 'foo.js', { line: 11, column: 12 });
       new Lexer(source).advance();
     } catch (error) {
       caughtError = error;
     }
     expect(String(caughtError)).to.equal(dedent`
-      Syntax Error: Cannot parse the unexpected character "?".
+      Syntax Error: Cannot parse the unexpected character "~".
 
       foo.js:13:6
       12 |
-      13 |      ?
+      13 |      ~
          |      ^
       14 |
     `);
@@ -200,16 +200,16 @@ describe('Lexer', () => {
   it('updates column numbers in error for file context', () => {
     let caughtError;
     try {
-      const source = new Source('?', 'foo.js', { line: 1, column: 5 });
+      const source = new Source('~', 'foo.js', { line: 1, column: 5 });
       new Lexer(source).advance();
     } catch (error) {
       caughtError = error;
     }
     expect(String(caughtError)).to.equal(dedent`
-      Syntax Error: Cannot parse the unexpected character "?".
+      Syntax Error: Cannot parse the unexpected character "~".
 
       foo.js:1:5
-      1 |     ?
+      1 |     ~
         |     ^
     `);
   });
@@ -820,8 +820,8 @@ describe('Lexer', () => {
       locations: [{ line: 1, column: 1 }],
     });
 
-    expectSyntaxError('?').to.deep.equal({
-      message: 'Syntax Error: Cannot parse the unexpected character "?".',
+    expectSyntaxError('~').to.deep.equal({
+      message: 'Syntax Error: Cannot parse the unexpected character "~".',
       locations: [{ line: 1, column: 1 }],
     });
 

src/language/__tests__/parser-test.ts

@@ -205,6 +205,56 @@ describe('Parser', () => {
     ).to.not.throw();
   });
 
+  it('parses required field', () => {
+    expect(() =>
+      parse(`
+      query {
+        requiredField!
+      }
+    `),
+    ).to.not.throw();
+  });
+
+  it('parses optional field', () => {
+    expect(() =>
+      parse(`
+      query {
+        optionalField?
+      }
+    `),
+    ).to.not.throw();
+  });
+
+  it('parses required with alias', () => {
+    expect(() =>
+      parse(`
+      query {
+        requiredField: field!
+      }
+    `),
+    ).to.not.throw();
+  });
+
+  it('does not parse aliased field with bang on left of colon', () => {
+    expect(() =>
+      parse(`
+      query {
+        requiredField!: field
+      }
+    `),
+    ).to.throw();
+  });
+
+  it('does not parse aliased field with bang on left and right of colon', () => {
+    expect(() =>
+      parse(`
+      query {
+        requiredField!: field!
+      }
+    `),
+    ).to.throw();
+  });
+
   it('creates ast', () => {
     const result = parse(dedent`
       {
@@ -256,6 +306,7 @@ describe('Parser', () => {
                   },
                 ],
                 directives: [],
+                required: 'unset',
                 selectionSet: {
                   kind: Kind.SELECTION_SET,
                   loc: { start: 16, end: 38 },
@@ -271,6 +322,7 @@ describe('Parser', () => {
                       },
                       arguments: [],
                       directives: [],
+                      required: 'unset',
                       selectionSet: undefined,
                     },
                     {
@@ -284,6 +336,7 @@ describe('Parser', () => {
                       },
                       arguments: [],
                       directives: [],
+                      required: 'unset',
                       selectionSet: undefined,
                     },
                   ],
@@ -331,6 +384,7 @@ describe('Parser', () => {
                 },
                 arguments: [],
                 directives: [],
+                required: 'unset',
                 selectionSet: {
                   kind: Kind.SELECTION_SET,
                   loc: { start: 15, end: 27 },
@@ -346,6 +400,7 @@ describe('Parser', () => {
                       },
                       arguments: [],
                       directives: [],
+                      required: 'unset',
                       selectionSet: undefined,
                     },
                   ],

src/language/__tests__/printer-test.ts

@@ -3,6 +3,7 @@ import { describe, it } from 'mocha';
 
 import { dedent, dedentString } from '../../__testUtils__/dedent';
 import { kitchenSinkQuery } from '../../__testUtils__/kitchenSinkQuery';
+import type { FieldNode } from '../ast';
 
 import { parse } from '../parser';
 import { print } from '../printer';
@@ -164,6 +165,10 @@ describe('Printer: Query document', () => {
                 ...frag @onFragmentSpread
               }
             }
+            field3!
+            requiredField4: field4!
+            field5?
+            optionalField6: field6?
           }
           ... @skip(unless: $foo) {
             id

src/language/__tests__/visitor-test.ts

@@ -661,6 +661,26 @@ describe('Visitor', () => {
       ['leave', 'Field', 1, undefined],
       ['leave', 'SelectionSet', 'selectionSet', 'Field'],
       ['leave', 'Field', 0, undefined],
+      ['enter', 'Field', 1, undefined],
+      ['enter', 'Name', 'name', 'Field'],
+      ['leave', 'Name', 'name', 'Field'],
+      ['leave', 'Field', 1, undefined],
+      ['enter', 'Field', 2, undefined],
+      ['enter', 'Name', 'alias', 'Field'],
+      ['leave', 'Name', 'alias', 'Field'],
+      ['enter', 'Name', 'name', 'Field'],
+      ['leave', 'Name', 'name', 'Field'],
+      ['leave', 'Field', 2, undefined],
+      ['enter', 'Field', 3, undefined],
+      ['enter', 'Name', 'name', 'Field'],
+      ['leave', 'Name', 'name', 'Field'],
+      ['leave', 'Field', 3, undefined],
+      ['enter', 'Field', 4, undefined],
+      ['enter', 'Name', 'alias', 'Field'],
+      ['leave', 'Name', 'alias', 'Field'],
+      ['enter', 'Name', 'name', 'Field'],
+      ['leave', 'Name', 'name', 'Field'],
+      ['leave', 'Field', 4, undefined],
       ['leave', 'SelectionSet', 'selectionSet', 'InlineFragment'],
       ['leave', 'InlineFragment', 1, undefined],
       ['enter', 'InlineFragment', 2, undefined],

src/language/ast.ts

@@ -288,6 +288,8 @@ export interface SelectionSetNode {
 
 export type SelectionNode = FieldNode | FragmentSpreadNode | InlineFragmentNode;
 
+export type RequiredStatus = 'required' | 'optional' | 'unset';
+
 export interface FieldNode {
   readonly kind: 'Field';
   readonly loc?: Location;
@@ -296,6 +298,7 @@ export interface FieldNode {
   readonly arguments?: ReadonlyArray<ArgumentNode>;
   readonly directives?: ReadonlyArray<DirectiveNode>;
   readonly selectionSet?: SelectionSetNode;
+  readonly required?: RequiredStatus;
 }
 
 export interface ArgumentNode {

src/language/index.ts

@@ -85,6 +85,7 @@ export type {
   UnionTypeExtensionNode,
   EnumTypeExtensionNode,
   InputObjectTypeExtensionNode,
+  RequiredStatus,
 } from './ast';
 
 export {

src/language/lexer.ts

@@ -204,6 +204,8 @@ function readToken(lexer: Lexer, prev: Token): Token {
       case 56: //  8
       case 57: //  9
         return readNumber(source, pos, code, line, col, prev);
+      case 63: //  ?
+        return new Token(TokenKind.QUESTION_MARK, pos, pos + 1, line, col, prev);
       case 65: //  A
       case 66: //  B
       case 67: //  C

src/language/parser.ts

@@ -348,7 +348,7 @@ export class Parser {
   /**
    * SelectionSet : { Selection+ }
    */
-  parseSelectionSet(): SelectionSetNode {
+  parseSelectionSet(): SelectionSetNode {   
     return this.node<SelectionSetNode>(this._lexer.token, {
       kind: Kind.SELECTION_SET,
       selections: this.many(
@@ -382,13 +382,23 @@ export class Parser {
     const nameOrAlias = this.parseName();
     let alias;
     let name;
+
     if (this.expectOptionalToken(TokenKind.COLON)) {
       alias = nameOrAlias;
       name = this.parseName();
     } else {
       name = nameOrAlias;
     }
 
+    let required;
+    if (this.expectOptionalToken(TokenKind.BANG)) {
+      required = 'required'
+    } else if (this.expectOptionalToken(TokenKind.QUESTION_MARK)) {
+      required = 'optional'
+    } else {
+      required = 'unset'
+    }
+
     return this.node<FieldNode>(start, {
       kind: Kind.FIELD,
       alias,
@@ -398,6 +408,7 @@ export class Parser {
       selectionSet: this.peek(TokenKind.BRACE_L)
         ? this.parseSelectionSet()
         : undefined,
+      required,
     });
   }
 

src/language/printer.ts

@@ -54,8 +54,14 @@ const printDocASTReducer: ASTReducer<string> = {
   SelectionSet: { leave: ({ selections }) => block(selections) },
 
   Field: {
-    leave({ alias, name, arguments: args, directives, selectionSet }) {
-      const prefix = wrap('', alias, ': ') + name;
+    leave({ alias, name, arguments: args, directives, selectionSet, required }) {
+      let prefix = wrap('', alias, ': ') + name;
+      if (required === 'required') {
+        prefix += '!'
+      } else if (required === 'optional') {
+        prefix += '?'
+      }
+
       let argsLine = prefix + wrap('(', join(args, ', '), ')');
 
       if (argsLine.length > MAX_LINE_LENGTH) {

src/language/tokenKind.ts

@@ -25,6 +25,7 @@ export const TokenKind = Object.freeze({
   STRING: 'String',
   BLOCK_STRING: 'BlockString',
   COMMENT: 'Comment',
+  QUESTION_MARK: '?',
 } as const);
 
 /**