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Update: add option "allowInParentheses" to no-sequences (fixes #14197) (#14199)
* New: add option "allowInParentheses" to rule "no-sequences" * added documentation * [no-equence]: switch default of "allowInParentheses" to true * restored removed sentence * changes from code review * code review
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‎docs/rules/no-sequences.md‎

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@@ -17,7 +17,7 @@ while (a = next(), a && a.length);
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This rule forbids the use of the comma operator, with the following exceptions:
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* In the initialization or update portions of a `for` statement.
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* If the expression sequence is explicitly wrapped in parentheses.
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* By default, if the expression sequence is explicitly wrapped in parentheses. This exception can be removed with the `allowInParentheses` option.
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Examples of **incorrect** code for this rule:
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@@ -63,10 +63,48 @@ while ((val = foo(), val < 42));
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with ((doSomething(), val)) {}
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```
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## Options
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This rule takes one option, an object, with the following properties:
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* `"allowInParentheses"`: If set to `true` (default), this rule allows expression sequences that are explicitly wrapped in parentheses.
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### allowInParentheses
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Examples of **incorrect** code for this rule with the `{ "allowInParentheses": false }` option:
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```js
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/*eslint no-sequences: ["error", { "allowInParentheses": false }]*/
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foo = (doSomething(), val);
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(0, eval)("doSomething();");
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do {} while ((doSomething(), !!test));
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for (; (doSomething(), !!test); );
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if ((doSomething(), !!test));
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switch ((val = foo(), val)) {}
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while ((val = foo(), val < 42));
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with ((doSomething(), val)) {}
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```
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Examples of **correct** code for this rule with the `{ "allowInParentheses": false }` option:
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```js
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/*eslint no-sequences: ["error", { "allowInParentheses": false }]*/
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for (i = 0, j = 10; i < j; i++, j--);
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```
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## When Not To Use It
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Disable this rule if sequence expressions with the comma operator are acceptable.
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Another case is where you might want to report all usages of the comma operator, even if they are wrapped in parentheses or in a for loop. You can achieve this using rule `no-restricted-syntax`:
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Another case is where you might want to report all usages of the comma operator, even in a for loop. You can achieve this using rule `no-restricted-syntax`:
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```js
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{

‎lib/rules/no-sequences.js‎

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const astUtils = require("./utils/ast-utils");
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//------------------------------------------------------------------------------
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// Helpers
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//------------------------------------------------------------------------------
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const DEFAULT_OPTIONS = {
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allowInParentheses: true
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};
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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url: "https://eslint.org/docs/rules/no-sequences"
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},
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schema: [],
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schema: [{
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properties: {
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allowInParentheses: {
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type: "boolean",
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default: true
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}
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},
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additionalProperties: false
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}],
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messages: {
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unexpectedCommaExpression: "Unexpected use of comma operator."
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}
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},
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create(context) {
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const options = Object.assign({}, DEFAULT_OPTIONS, context.options[0]);
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const sourceCode = context.getSourceCode();
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/**
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}
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// Wrapping a sequence in extra parens indicates intent
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if (requiresExtraParens(node)) {
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if (isParenthesisedTwice(node)) {
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return;
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}
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} else {
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if (isParenthesised(node)) {
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return;
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if (options.allowInParentheses) {
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if (requiresExtraParens(node)) {
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if (isParenthesisedTwice(node)) {
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return;
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}
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} else {
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if (isParenthesised(node)) {
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return;
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}
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}
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}
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‎tests/lib/rules/no-sequences.js‎

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@@ -46,10 +46,20 @@ ruleTester.run("no-sequences", rule, {
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"do {} while ((doSomething(), !!test));",
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"for ((doSomething(), somethingElse()); (doSomething(), !!test); );",
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"if ((doSomething(), !!test));",
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"switch ((doSomething(), !!test)) {}",
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"switch ((doSomething(), val)) {}",
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"while ((doSomething(), !!test));",
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"with ((doSomething(), val)) {}",
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{ code: "a => ((doSomething(), a))", env: { es6: true } }
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{ code: "a => ((doSomething(), a))", env: { es6: true } },
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// options object without "allowInParentheses" property
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{ code: "var foo = (1, 2);", options: [{}] },
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// explicitly set option "allowInParentheses" to default value
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{ code: "var foo = (1, 2);", options: [{ allowInParentheses: true }] },
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// valid code with "allowInParentheses" set to `false`
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{ code: "for ((i = 0, j = 0); test; );", options: [{ allowInParentheses: false }] },
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{ code: "for (; test; (i++, j++));", options: [{ allowInParentheses: false }] }
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],
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// Examples of code that should trigger the rule
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{ code: "a => (doSomething(), a)", env: { es6: true }, errors: errors(20) },
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{ code: "(1), 2", errors: errors(4) },
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{ code: "((1)) , (2)", errors: errors(7) },
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{ code: "while((1) , 2);", errors: errors(11) }
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{ code: "while((1) , 2);", errors: errors(11) },
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// option "allowInParentheses": do not allow sequence in parentheses
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{ code: "var foo = (1, 2);", options: [{ allowInParentheses: false }], errors: errors(13) },
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{ code: "(0,eval)(\"foo()\");", options: [{ allowInParentheses: false }], errors: errors(3) },
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{ code: "foo(a, (b, c), d);", options: [{ allowInParentheses: false }], errors: errors(10) },
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{ code: "do {} while ((doSomething(), !!test));", options: [{ allowInParentheses: false }], errors: errors(28) },
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{ code: "for (; (doSomething(), !!test); );", options: [{ allowInParentheses: false }], errors: errors(22) },
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{ code: "if ((doSomething(), !!test));", options: [{ allowInParentheses: false }], errors: errors(19) },
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{ code: "switch ((doSomething(), val)) {}", options: [{ allowInParentheses: false }], errors: errors(23) },
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{ code: "while ((doSomething(), !!test));", options: [{ allowInParentheses: false }], errors: errors(22) },
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{ code: "with ((doSomething(), val)) {}", options: [{ allowInParentheses: false }], errors: errors(21) },
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{ code: "a => ((doSomething(), a))", options: [{ allowInParentheses: false }], env: { es6: true }, errors: errors(21) }
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]
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});

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