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Add no-unnecessary-array-flat-depth rule (#2618)
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‎docs/rules/no-unnecessary-array-flat-depth.md‎

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# Disallow using `1` as the `depth` argument of `Array#flat()`
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💼 This rule is enabled in the ✅ `recommended` [config](https://github.com/sindresorhus/eslint-plugin-unicorn#recommended-config).
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🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
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<!-- end auto-generated rule header -->
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<!-- Do not manually modify this header. Run: `npm run fix:eslint-docs` -->
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Passing `1` as the `depth` argument to [`Array#flat(depth)`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat) is unnecessary.
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## Examples
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```js
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// ❌
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foo.flat(1);
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// ✅
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foo.flat();
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```
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```js
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// ❌
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foo?.flat(1);
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// ✅
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foo?.flat();
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```

‎docs/rules/no-unnecessary-array-splice-count.md‎

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<!-- Remove this comment, add more detailed description. -->
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When calling `Array#splice(start, deleteCount)` and `Array#toSpliced(start, skipCount)`, omitting the `deleteCount` and `skipCount` argument will delete or skip all elements after `start`. Using `.length` or `Infinity` is unnecessary.
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When calling [`Array#splice(start, deleteCount)`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice) and [`Array#toSpliced(start, skipCount)`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toSpliced), omitting the `deleteCount` and `skipCount` argument will delete or skip all elements after `start`. Using `.length` or `Infinity` is unnecessary.
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## Examples
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‎readme.md‎

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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-typeof-undefined](docs/rules/no-typeof-undefined.md) | Disallow comparing `undefined` using `typeof`. | ✅ | 🔧 | 💡 |
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| [no-unnecessary-array-flat-depth](docs/rules/no-unnecessary-array-flat-depth.md) | Disallow using `1` as the `depth` argument of `Array#flat()`. | ✅ | 🔧 | |
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| [no-unnecessary-array-splice-count](docs/rules/no-unnecessary-array-splice-count.md) | Disallow using `.length` or `Infinity` as the `deleteCount` or `skipCount` argument of `Array#{splice,toSpliced}()`. | ✅ | 🔧 | |
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| [no-unnecessary-await](docs/rules/no-unnecessary-await.md) | Disallow awaiting non-promise values. | ✅ | 🔧 | |
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| [no-unnecessary-polyfills](docs/rules/no-unnecessary-polyfills.md) | Enforce the use of built-in methods instead of unnecessary polyfills. | ✅ | | |

‎rules/index.js‎

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@@ -53,6 +53,7 @@ import noStaticOnlyClass from './no-static-only-class.js';
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import noThenable from './no-thenable.js';
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import noThisAssignment from './no-this-assignment.js';
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import noTypeofUndefined from './no-typeof-undefined.js';
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import noUnnecessaryArrayFlatDepth from './no-unnecessary-array-flat-depth.js';
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import noUnnecessaryArraySpliceCount from './no-unnecessary-array-splice-count.js';
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import noUnnecessaryAwait from './no-unnecessary-await.js';
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import noUnnecessaryPolyfills from './no-unnecessary-polyfills.js';
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'no-thenable': createRule(noThenable, 'no-thenable'),
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'no-this-assignment': createRule(noThisAssignment, 'no-this-assignment'),
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'no-typeof-undefined': createRule(noTypeofUndefined, 'no-typeof-undefined'),
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'no-unnecessary-array-flat-depth': createRule(noUnnecessaryArrayFlatDepth, 'no-unnecessary-array-flat-depth'),
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'no-unnecessary-array-splice-count': createRule(noUnnecessaryArraySpliceCount, 'no-unnecessary-array-splice-count'),
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'no-unnecessary-await': createRule(noUnnecessaryAwait, 'no-unnecessary-await'),
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'no-unnecessary-polyfills': createRule(noUnnecessaryPolyfills, 'no-unnecessary-polyfills'),

‎rules/no-unnecessary-array-flat-depth.js‎

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import {isMethodCall, isLiteral} from './ast/index.js';
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import {removeArgument} from './fix/index.js';
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import {} from './utils/index.js';
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const MESSAGE_ID = 'no-unnecessary-array-flat-depth';
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const messages = {
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[MESSAGE_ID]: 'Passing `1` as the `depth` argument is unnecessary.',
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};
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/** @param {import('eslint').Rule.RuleContext} context */
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const create = context => {
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context.on('CallExpression', callExpression => {
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if (!(
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isMethodCall(callExpression, {
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method: 'flat',
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argumentsLength: 1,
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optionalCall: false,
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})
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&& isLiteral(callExpression.arguments[0], 1)
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)) {
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return;
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}
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const [numberOne] = callExpression.arguments;
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return {
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node: numberOne,
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messageId: MESSAGE_ID,
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/** @param {import('eslint').Rule.RuleFixer} fixer */
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fix: fixer => removeArgument(fixer, numberOne, context.sourceCode),
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};
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});
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};
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/** @type {import('eslint').Rule.RuleModule} */
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const config = {
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create,
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meta: {
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type: 'suggestion',
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docs: {
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description: 'Disallow using `1` as the `depth` argument of `Array#flat()`.',
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recommended: true,
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},
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fixable: 'code',
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messages,
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},
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};
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export default config;

‎test/no-unnecessary-array-flat-depth.js‎

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import {getTester} from './utils/test.js';
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const {test} = getTester(import.meta);
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test.snapshot({
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valid: [
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'foo.flat()',
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'foo.flat?.(1)',
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'foo?.flat()',
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'foo.flat(1, extra)',
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'flat(1)',
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'new foo.flat(1)',
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'const ONE = 1; foo.flat(ONE)',
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'foo.notFlat(1)',
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],
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invalid: [
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'foo.flat(1)',
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'foo.flat(1.0)',
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'foo.flat(0b01)',
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'foo?.flat(1)',
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],
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});

‎test/snapshots/no-unnecessary-array-flat-depth.js.md‎

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# Snapshot report for `test/no-unnecessary-array-flat-depth.js`
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The actual snapshot is saved in `no-unnecessary-array-flat-depth.js.snap`.
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Generated by [AVA](https://avajs.dev).
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## invalid(1): foo.flat(1)
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> Input
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`␊
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1 | foo.flat(1)␊
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`
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> Output
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`␊
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1 | foo.flat()␊
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`
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> Error 1/1
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`␊
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> 1 | foo.flat(1)␊
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| ^ Passing \`1\` as the \`depth\` argument is unnecessary.␊
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`
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## invalid(2): foo.flat(1.0)
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> Input
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`␊
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1 | foo.flat(1.0)␊
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`
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> Output
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`␊
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1 | foo.flat()␊
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`
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> Error 1/1
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`␊
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> 1 | foo.flat(1.0)␊
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| ^^^ Passing \`1\` as the \`depth\` argument is unnecessary.␊
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`
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## invalid(3): foo.flat(0b01)
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> Input
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`␊
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1 | foo.flat(0b01)␊
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`
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> Output
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`␊
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1 | foo.flat()␊
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`
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> Error 1/1
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`␊
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> 1 | foo.flat(0b01)␊
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| ^^^^ Passing \`1\` as the \`depth\` argument is unnecessary.␊
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`
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## invalid(4): foo?.flat(1)
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> Input
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`␊
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1 | foo?.flat(1)␊
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`
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> Output
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`␊
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1 | foo?.flat()␊
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`
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> Error 1/1
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`␊
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> 1 | foo?.flat(1)␊
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| ^ Passing \`1\` as the \`depth\` argument is unnecessary.␊
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`
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## invalid(3): foo?.flat(1)
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> Input
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`␊
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1 | foo?.flat(1)␊
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`
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> Output
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`␊
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1 | foo?.flat()␊
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`
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> Error 1/1
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`␊
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> 1 | foo?.flat(1)␊
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| ^ Passing \`1\` as the \`depth\` argument is unnecessary.␊
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`

‎test/snapshots/no-unnecessary-array-flat-depth.js.snap‎

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