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Add no-unnecessary-await rule (#1904)
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+1002
-38
lines changed

‎configs/recommended.js

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@@ -50,6 +50,7 @@ module.exports = {
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'unicorn/no-static-only-class': 'error',
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'unicorn/no-thenable': 'error',
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'unicorn/no-this-assignment': 'error',
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'unicorn/no-unnecessary-await': 'error',
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'unicorn/no-unreadable-array-destructuring': 'error',
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'unicorn/no-unreadable-iife': 'error',
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'unicorn/no-unsafe-regex': 'off',

‎docs/rules/no-unnecessary-await.md

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# Disallow awaiting non-promise values
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<!-- Do not manually modify RULE_NOTICE part. Run: `npm run generate-rule-notices` -->
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<!-- RULE_NOTICE -->
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✅ *This rule is part of the [recommended](https://github.com/sindresorhus/eslint-plugin-unicorn#recommended-config) config.*
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🔧 *This rule is [auto-fixable](https://eslint.org/docs/user-guide/command-line-interface#fixing-problems).*
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<!-- /RULE_NOTICE -->
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The [`await` operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await) should only be used on [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) values.
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## Fail
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```js
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await await promise;
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```
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```js
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await [promise1, promise2];
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```
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## Pass
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```js
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await promise;
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```
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```js
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await Promise.allSettled([promise1, promise2]);
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```

‎readme.md

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@@ -91,6 +91,7 @@ Each rule has emojis denoting:
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| [no-static-only-class](docs/rules/no-static-only-class.md) | Disallow classes that only have static members. | ✅ | 🔧 | |
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| [no-thenable](docs/rules/no-thenable.md) | Disallow `then` property. | ✅ | | |
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| [no-this-assignment](docs/rules/no-this-assignment.md) | Disallow assigning `this` to a variable. | ✅ | | |
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| [no-unnecessary-await](docs/rules/no-unnecessary-await.md) | Disallow awaiting non-promise values. | ✅ | 🔧 | |
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| [no-unreadable-array-destructuring](docs/rules/no-unreadable-array-destructuring.md) | Disallow unreadable array destructuring. | ✅ | 🔧 | |
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| [no-unreadable-iife](docs/rules/no-unreadable-iife.md) | Disallow unreadable IIFEs. | ✅ | | |
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| [no-unsafe-regex](docs/rules/no-unsafe-regex.md) | Disallow unsafe regular expressions. | | | |

‎rules/fix/add-parenthesizes-to-return-or-throw-expression.js

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'use strict';
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const {isSemicolonToken} = require('eslint-utils');
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function * addParenthesizesToReturnOrThrowExpression(fixer, node, sourceCode) {
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if (node.type !== 'ReturnStatement' && node.type !== 'ThrowStatement') {
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return;
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}
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const returnOrThrowToken = sourceCode.getFirstToken(node);
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yield fixer.insertTextAfter(returnOrThrowToken, ' (');
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const lastToken = sourceCode.getLastToken(node);
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if (!isSemicolonToken(lastToken)) {
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yield fixer.insertTextAfter(node, ')');
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return;
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}
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yield fixer.insertTextBefore(lastToken, ')');
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}
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module.exports = addParenthesizesToReturnOrThrowExpression;

‎rules/fix/index.js

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@@ -19,4 +19,5 @@ module.exports = {
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removeSpacesAfter: require('./remove-spaces-after.js'),
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fixSpaceAroundKeyword: require('./fix-space-around-keywords.js'),
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replaceStringLiteral: require('./replace-string-literal.js'),
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addParenthesizesToReturnOrThrowExpression: require('./add-parenthesizes-to-return-or-throw-expression.js'),
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};

‎rules/fix/remove-spaces-after.js

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@@ -1,9 +1,9 @@
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'use strict';
22

3-
function removeSpacesAfter(indexOrNode, sourceCode, fixer) {
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let index = indexOrNode;
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if (typeof indexOrNode === 'object' && Array.isArray(indexOrNode.range)) {
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index = indexOrNode.range[1];
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function removeSpacesAfter(indexOrNodeOrToken, sourceCode, fixer) {
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let index = indexOrNodeOrToken;
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if (typeof indexOrNodeOrToken === 'object' && Array.isArray(indexOrNodeOrToken.range)) {
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index = indexOrNodeOrToken.range[1];
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}
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const textAfter = sourceCode.text.slice(index);

‎rules/fix/switch-new-expression-to-call-expression.js

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@@ -1,41 +1,17 @@
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'use strict';
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const isNewExpressionWithParentheses = require('../utils/is-new-expression-with-parentheses.js');
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const {isParenthesized} = require('../utils/parentheses.js');
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const isOnSameLine = require('../utils/is-on-same-line.js');
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const addParenthesizesToReturnOrThrowExpression = require('./add-parenthesizes-to-return-or-throw-expression.js');
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const removeSpaceAfter = require('./remove-spaces-after.js');
47

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function * fixReturnOrThrowStatementArgument(newExpression, sourceCode, fixer) {
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const {parent} = newExpression;
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if (
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(parent.type !== 'ReturnStatement' && parent.type !== 'ThrowStatement')
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|| parent.argument !== newExpression
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|| isParenthesized(newExpression, sourceCode)
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) {
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return;
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}
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const returnStatement = parent;
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const returnToken = sourceCode.getFirstToken(returnStatement);
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const classNode = newExpression.callee;
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// Ideally, we should use first parenthesis of the `callee`, and should check spaces after the `new` token
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// But adding extra parentheses is harmless, no need to be too complicated
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if (returnToken.loc.start.line === classNode.loc.start.line) {
22-
return;
23-
}
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function * switchNewExpressionToCallExpression(newExpression, sourceCode, fixer) {
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const newToken = sourceCode.getFirstToken(newExpression);
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yield fixer.remove(newToken);
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yield removeSpaceAfter(newToken, sourceCode, fixer);
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25-
yield fixer.insertTextAfter(returnToken, ' (');
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yield fixer.insertTextAfter(newExpression, ')');
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}
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function * switchNewExpressionToCallExpression(node, sourceCode, fixer) {
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const [start] = node.range;
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let end = start + 3; // `3` = length of `new`
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const textAfter = sourceCode.text.slice(end);
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const [leadingSpaces] = textAfter.match(/^\s*/);
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end += leadingSpaces.length;
35-
yield fixer.removeRange([start, end]);
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37-
if (!isNewExpressionWithParentheses(node, sourceCode)) {
38-
yield fixer.insertTextAfter(node, '()');
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if (!isNewExpressionWithParentheses(newExpression, sourceCode)) {
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yield fixer.insertTextAfter(newExpression, '()');
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}
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/*
@@ -48,7 +24,11 @@ function * switchNewExpressionToCallExpression(node, sourceCode, fixer) {
4824
}
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```
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*/
51-
yield * fixReturnOrThrowStatementArgument(node, sourceCode, fixer);
27+
if (!isOnSameLine(newToken, newExpression.callee) && !isParenthesized(newExpression, sourceCode)) {
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// Ideally, we should use first parenthesis of the `callee`, and should check spaces after the `new` token
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// But adding extra parentheses is harmless, no need to be too complicated
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yield * addParenthesizesToReturnOrThrowExpression(fixer, newExpression.parent, sourceCode);
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}
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}
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5434
module.exports = switchNewExpressionToCallExpression;

‎rules/no-unnecessary-await.js

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'use strict';
2+
const {
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addParenthesizesToReturnOrThrowExpression,
4+
removeSpacesAfter,
5+
} = require('./fix/index.js');
6+
const {isParenthesized} = require('./utils/parentheses.js');
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const needsSemicolon = require('./utils/needs-semicolon.js');
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const isOnSameLine = require('./utils/is-on-same-line.js');
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const MESSAGE_ID = 'no-unnecessary-await';
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const messages = {
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[MESSAGE_ID]: 'Do not `await` non-promise value.',
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};
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function notPromise(node) {
16+
switch (node.type) {
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case 'ArrayExpression':
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case 'ArrowFunctionExpression':
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case 'AwaitExpression':
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case 'BinaryExpression':
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case 'ClassExpression':
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case 'FunctionExpression':
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case 'JSXElement':
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case 'JSXFragment':
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case 'Literal':
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case 'TemplateLiteral':
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case 'UnaryExpression':
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case 'UpdateExpression':
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return true;
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case 'SequenceExpression':
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return notPromise(node.expressions[node.expressions.length - 1]);
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// No default
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}
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return false;
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}
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/** @param {import('eslint').Rule.RuleContext} context */
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const create = context => ({
40+
AwaitExpression(node) {
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if (!notPromise(node.argument)) {
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return;
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}
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const sourceCode = context.getSourceCode();
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const awaitToken = sourceCode.getFirstToken(node);
47+
const problem = {
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node,
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loc: awaitToken.loc,
50+
messageId: MESSAGE_ID,
51+
};
52+
53+
const valueNode = node.argument;
54+
if (
55+
// Removing `await` may change them to a declaration, if there is no `id` will cause SyntaxError
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valueNode.type === 'FunctionExpression'
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|| valueNode.type === 'ClassExpression'
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// `+await +1` -> `++1`
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|| (
60+
node.parent.type === 'UnaryExpression'
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&& valueNode.type === 'UnaryExpression'
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&& node.parent.operator === valueNode.operator
63+
)
64+
) {
65+
return problem;
66+
}
67+
68+
return Object.assign(problem, {
69+
/** @param {import('eslint').Rule.RuleFixer} fixer */
70+
* fix(fixer) {
71+
if (
72+
!isOnSameLine(awaitToken, valueNode)
73+
&& !isParenthesized(node, sourceCode)
74+
) {
75+
yield * addParenthesizesToReturnOrThrowExpression(fixer, node.parent, sourceCode);
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}
77+
78+
yield fixer.remove(awaitToken);
79+
yield removeSpacesAfter(awaitToken, sourceCode, fixer);
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const nextToken = sourceCode.getTokenAfter(awaitToken);
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const tokenBefore = sourceCode.getTokenBefore(awaitToken);
83+
if (needsSemicolon(tokenBefore, sourceCode, nextToken.value)) {
84+
yield fixer.insertTextBefore(nextToken, ';');
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}
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},
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});
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},
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});
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91+
/** @type {import('eslint').Rule.RuleModule} */
92+
module.exports = {
93+
create,
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meta: {
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type: 'suggestion',
96+
docs: {
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description: 'Disallow awaiting non-promise values.',
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},
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fixable: 'code',
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messages,
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},
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};

‎rules/utils/is-on-same-line.js

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'use strict';
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3+
function isOnSameLine(nodeOrTokenA, nodeOrTokenB) {
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return nodeOrTokenA.loc.start.line === nodeOrTokenB.loc.start.line;
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}
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module.exports = isOnSameLine;

‎test/no-unnecessary-await.mjs

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import outdent from 'outdent';
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import {getTester} from './utils/test.mjs';
3+
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const {test} = getTester(import.meta);
5+
6+
test.snapshot({
7+
testerOptions: {
8+
parserOptions: {
9+
ecmaFeatures: {
10+
jsx: true,
11+
},
12+
},
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},
14+
valid: [
15+
'await {then}',
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'await a ? b : c',
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'await a || b',
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'await a && b',
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'await a ?? b',
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'await new Foo()',
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'await tagged``',
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'class A { async foo() { await this }}',
23+
'async function * foo() {await (yield bar);}',
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'await (1, Promise.resolve())',
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],
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invalid: [
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'await []',
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'await [Promise.resolve()]',
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'await (() => {})',
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'await (() => Promise.resolve())',
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'await (a === b)',
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'await (a instanceof Promise)',
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'await (a > b)',
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'await class {}',
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'await class extends Promise {}',
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'await function() {}',
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'await function name() {}',
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'await function() { return Promise.resolve() }',
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'await (<></>)',
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'await (<a></a>)',
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'await 0',
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'await 1',
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'await ""',
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'await "string"',
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'await true',
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'await false',
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'await null',
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'await 0n',
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'await 1n',
50+
// eslint-disable-next-line no-template-curly-in-string
51+
'await `${Promise.resolve()}`',
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'await !Promise.resolve()',
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'await void Promise.resolve()',
54+
'await +Promise.resolve()',
55+
'await ~1',
56+
'await ++foo',
57+
'await foo--',
58+
'await (Promise.resolve(), 1)',
59+
outdent`
60+
async function foo() {
61+
return await
62+
// comment
63+
1;
64+
}
65+
`,
66+
outdent`
67+
async function foo() {
68+
return await
69+
// comment
70+
1
71+
}
72+
`,
73+
outdent`
74+
async function foo() {
75+
return( await
76+
// comment
77+
1);
78+
}
79+
`,
80+
outdent`
81+
foo()
82+
await []
83+
`,
84+
outdent`
85+
foo()
86+
await +1
87+
`,
88+
outdent`
89+
async function foo() {
90+
return await
91+
// comment
92+
[];
93+
}
94+
`,
95+
outdent`
96+
async function foo() {
97+
throw await
98+
// comment
99+
1;
100+
}
101+
`,
102+
outdent`
103+
console.log(
104+
await
105+
// comment
106+
[]
107+
);
108+
`,
109+
'async function foo() {+await +1}',
110+
'async function foo() {-await-1}',
111+
'async function foo() {+await -1}',
112+
],
113+
});

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