feat(eslint-plugin): added new rule await-promise (#192)

packages/eslint-plugin/README.md

@@ -112,6 +112,7 @@ Then you should add `airbnb` (or `airbnb-base`) to your `extends` section of `.e
 | --------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------ | -------- | ----------------- |
 | [`@typescript-eslint/adjacent-overload-signatures`](./docs/rules/adjacent-overload-signatures.md)         | Require that member overloads be consecutive (`adjacent-overload-signatures` from TSLint)                                                           | :heavy_check_mark: |          |                   |
 | [`@typescript-eslint/array-type`](./docs/rules/array-type.md)                                             | Requires using either `T[]` or `Array<T>` for arrays (`array-type` from TSLint)                                                                     | :heavy_check_mark: | :wrench: |                   |
+| [`@typescript-eslint/await-thenable`](./docs/rules/await-thenable.md)                                     | Disallow awaiting a value that is not a Promise (`await-promise` from TSLint)                                                                       | :heavy_check_mark: |          | :thought_balloon: |
 | [`@typescript-eslint/ban-types`](./docs/rules/ban-types.md)                                               | Enforces that types will not to be used (`ban-types` from TSLint)                                                                                   | :heavy_check_mark: | :wrench: |                   |
 | [`@typescript-eslint/ban-ts-ignore`](./docs/rules/ban-ts-ignore.md)                                       | Bans “// @ts-ignore” comments from being used (`ban-ts-ignore` from TSLint)                                                                         |                    |          |                   |
 | [`@typescript-eslint/camelcase`](./docs/rules/camelcase.md)                                               | Enforce camelCase naming convention                                                                                                                 | :heavy_check_mark: |          |                   |

packages/eslint-plugin/ROADMAP.md

@@ -40,7 +40,7 @@
 
 | TSLint rule                          |     | ESLint rule                                                           |
 | ------------------------------------ | :-: | --------------------------------------------------------------------- |
-| [`await-promise`]                    | 🛑  | N/A                                                                   |
+| [`await-promise`]                    | ✅  | [`@typescript-eslint/await-thenable`]                                 |
 | [`ban-comma-operator`]               | 🌟  | [`no-sequences`][no-sequences]                                        |
 | [`ban`]                              | 🌟  | [`no-restricted-properties`][no-restricted-properties]                |
 | [`curly`]                            | 🌟  | [`curly`][curly]                                                      |
@@ -574,6 +574,7 @@ Relevant plugins: [`chai-expect-keywords`](https://github.com/gavinaiken/eslint-
 <!-- @typescript-eslint/eslint-plugin -->
 
 [`@typescript-eslint/adjacent-overload-signatures`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/adjacent-overload-signatures.md
+[`@typescript-eslint/await-thenable`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/await-thenable.md
 [`@typescript-eslint/ban-types`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/ban-types.md
 [`@typescript-eslint/ban-ts-ignore`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/ban-ts-ignore.md
 [`@typescript-eslint/explicit-member-accessibility`]: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/explicit-member-accessibility.md

packages/eslint-plugin/docs/rules/await-thenable.md

@@ -0,0 +1,33 @@
+# Disallows awaiting a value that is not a Promise (await-thenable)
+
+This rule disallows awaiting a value that is not a "Thenable" (an object which has `then` method, such as a Promise).
+While it is valid JavaScript to await a non-`Promise`-like value (it will resolve immediately), this pattern is often a programmer error, such as forgetting to add parenthesis to call a function that returns a Promise.
+
+## Rule Details
+
+Examples of **incorrect** code for this rule:
+
+```ts
+await 'value';
+
+const createValue = () => 'value';
+await createValue();
+```
+
+Examples of **correct** code for this rule:
+
+```ts
+await Promise.resolve('value');
+
+const createValue = async () => 'value';
+await createValue();
+```
+
+## When Not To Use It
+
+If you want to allow code to `await` non-Promise values.
+This is generally not preferred, but can sometimes be useful for visual consistency.
+
+## Related to
+
+- TSLint: ['await-promise'](https://palantir.github.io/tslint/rules/await-promise)

packages/eslint-plugin/src/rules/await-thenable.ts

@@ -0,0 +1,47 @@
+import * as tsutils from 'tsutils';
+import * as ts from 'typescript';
+
+import * as util from '../util';
+
+export default util.createRule({
+  name: 'await-thenable',
+  meta: {
+    docs: {
+      description: 'Disallows awaiting a value that is not a Thenable',
+      category: 'Best Practices',
+      recommended: 'error',
+      tslintName: 'await-thenable',
+    },
+    messages: {
+      await: 'Unexpected `await` of a non-Promise (non-"Thenable") value.',
+    },
+    schema: [],
+    type: 'problem',
+  },
+  defaultOptions: [],
+
+  create(context) {
+    const parserServices = util.getParserServices(context);
+    const checker = parserServices.program.getTypeChecker();
+
+    return {
+      AwaitExpression(node) {
+        const originalNode = parserServices.esTreeNodeToTSNodeMap.get(
+          node,
+        ) as ts.AwaitExpression;
+        const type = checker.getTypeAtLocation(originalNode.expression);
+
+        if (
+          !tsutils.isTypeFlagSet(type, ts.TypeFlags.Any) &&
+          !tsutils.isTypeFlagSet(type, ts.TypeFlags.Unknown) &&
+          !tsutils.isThenableType(checker, originalNode.expression, type)
+        ) {
+          context.report({
+            messageId: 'await',
+            node,
+          });
+        }
+      },
+    };
+  },
+});

packages/eslint-plugin/tests/rules/await-thenable.test.ts

@@ -0,0 +1,223 @@
+import rule from '../../src/rules/await-thenable';
+import { RuleTester, getFixturesRootDir } from '../RuleTester';
+
+const rootDir = getFixturesRootDir();
+const parserOptions = {
+  ecmaVersion: 2018,
+  tsconfigRootDir: rootDir,
+  project: './tsconfig.json',
+};
+
+const messageId = 'await';
+
+const ruleTester = new RuleTester({
+  parserOptions,
+  parser: '@typescript-eslint/parser',
+});
+
+ruleTester.run('await-promise', rule, {
+  valid: [
+    `
+async function test() {
+  await Promise.resolve("value");
+  await Promise.reject(new Error("message"));
+}
+`,
+    `
+async function test() {
+  await (async () => true)();
+}
+`,
+    `
+async function test() {
+  function returnsPromise() {
+    return Promise.resolve("value");
+  }
+  await returnsPromise();
+}
+`,
+    `
+async function test() {
+  async function returnsPromiseAsync() {}
+  await returnsPromiseAsync();
+}
+`,
+    `
+async function test() {
+  let anyValue: any;
+  await anyValue;
+}
+`,
+    `
+async function test() {
+  let unknownValue: unknown;
+  await unknownValue;
+}
+`,
+    `
+async function test() {
+  const numberPromise: Promise<number>;
+  await numberPromise;
+}
+`,
+    `
+async function test() {
+  class Foo extends Promise<number> {}
+  const foo: Foo = Foo.resolve(2);
+  await foo;
+
+  class Bar extends Foo {}
+  const bar: Bar = Bar.resolve(2);
+  await bar;
+}
+`,
+    `
+async function test() {
+  await (Math.random() > 0.5 ? numberPromise : 0);
+  await (Math.random() > 0.5 ? foo : 0);
+  await (Math.random() > 0.5 ? bar : 0);
+
+  const intersectionPromise: Promise<number> & number;
+  await intersectionPromise;
+}
+`,
+    `
+async function test() {
+  class Thenable { then(callback: () => {}) { } };
+  const thenable = new Thenable();
+
+  await thenable;
+}
+`,
+    `
+// https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/promise-polyfill/index.d.ts
+// Type definitions for promise-polyfill 6.0
+// Project: https://github.com/taylorhakes/promise-polyfill
+// Definitions by: Steve Jenkins <https://github.com/skysteve>
+//                 Daniel Cassidy <https://github.com/djcsdy>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+
+interface PromisePolyfillConstructor extends PromiseConstructor {
+    _immediateFn?: (handler: (() => void) | string) => void;
+}
+
+declare const PromisePolyfill: PromisePolyfillConstructor;
+
+async function test() {
+  const promise = new PromisePolyfill(() => {});
+
+  await promise;
+}
+`,
+    `
+// https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/bluebird/index.d.ts
+// Type definitions for bluebird 3.5
+// Project: https://github.com/petkaantonov/bluebird
+// Definitions by: Leonard Hecker <https://github.com/lhecker>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+// TypeScript Version: 2.8
+
+/*!
+ * The code following this comment originates from:
+ *   https://github.com/types/npm-bluebird
+ *
+ * Note for browser users: use bluebird-global typings instead of this one
+ * if you want to use Bluebird via the global Promise symbol.
+ *
+ * Licensed under:
+ *   The MIT License (MIT)
+ *
+ *   Copyright (c) 2016 unional
+ *
+ *   Permission is hereby granted, free of charge, to any person obtaining a copy
+ *   of this software and associated documentation files (the "Software"), to deal
+ *   in the Software without restriction, including without limitation the rights
+ *   to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ *   copies of the Software, and to permit persons to whom the Software is
+ *   furnished to do so, subject to the following conditions:
+ *
+ *   The above copyright notice and this permission notice shall be included in
+ *   all copies or substantial portions of the Software.
+ *
+ *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ *   AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ *   LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ *   OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ *   THE SOFTWARE.
+ */
+
+type Constructor<E> = new (...args: any[]) => E;
+type CatchFilter<E> = ((error: E) => boolean) | (object & E);
+type IterableItem<R> = R extends Iterable<infer U> ? U : never;
+type IterableOrNever<R> = Extract<R, Iterable<any>>;
+type Resolvable<R> = R | PromiseLike<R>;
+type IterateFunction<T, R> = (item: T, index: number, arrayLength: number) => Resolvable<R>;
+
+declare class Bluebird<R> implements PromiseLike<R> {
+  then<U>(onFulfill?: (value: R) => Resolvable<U>, onReject?: (error: any) => Resolvable<U>): Bluebird<U>; // For simpler signature help.
+  then<TResult1 = R, TResult2 = never>(
+      onfulfilled?: ((value: R) => Resolvable<TResult1>) | null,
+      onrejected?: ((reason: any) => Resolvable<TResult2>) | null
+    ): Bluebird<TResult1 | TResult2>;
+}
+
+declare const bluebird: Bluebird;
+
+async function test() {
+  await bluebird;
+}
+`,
+  ],
+
+  invalid: [
+    {
+      code: `
+async function test() {
+  await 0;
+  await "value";
+
+  await (Math.random() > 0.5 ? "" : 0);
+
+  class NonPromise extends Array {}
+  await new NonPromise();
+}
+`,
+      errors: [
+        {
+          line: 3,
+          messageId,
+        },
+        {
+          line: 4,
+          messageId,
+        },
+        {
+          line: 6,
+          messageId,
+        },
+        {
+          line: 9,
+          messageId,
+        },
+      ],
+    },
+    {
+      code: `
+async function test() {
+  class IncorrectThenable { then() { } };
+  const thenable = new IncorrectThenable();
+
+  await thenable;
+}
+      `,
+      errors: [
+        {
+          line: 6,
+          messageId,
+        },
+      ],
+    },
+  ],
+});