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feat(eslint-plugin): add no-unnecessary-boolean-literal-compare (#242)
Co-authored-by: Brad Zacher <brad.zacher@gmail.com>
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packages/eslint-plugin/docs/rules/no-unnecessary-boolean-literal-compare.md
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| # Flags unnecessary equality comparisons against boolean literals (`no-unnecessary-boolean-literal-compare`) | ||
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| Comparing boolean values to boolean literals is unnecessary, those comparisons result in the same booleans. Using the boolean values directly, or via a unary negation (`!value`), is more concise and clearer. | ||
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| ## Rule Details | ||
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| This rule ensures that you do not include unnecessary comparisons with boolean literals. | ||
| A comparison is considered unnecessary if it checks a boolean literal against any variable with just the `boolean` type. | ||
| A comparison is **_not_** considered unnecessary if the type is a union of booleans (`string | boolean`, `someObject | boolean`). | ||
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| Examples of **incorrect** code for this rule: | ||
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| ```ts | ||
| declare const someCondition: boolean; | ||
| if (someCondition === true) { | ||
| } | ||
| ``` | ||
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| Examples of **correct** code for this rule | ||
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| ```ts | ||
| declare const someCondition: boolean; | ||
| if (someCondition) { | ||
| } | ||
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| declare const someObjectBoolean: boolean | Record<string, unknown>; | ||
| if (someObjectBoolean === true) { | ||
| } | ||
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| declare const someStringBoolean: boolean | string; | ||
| if (someStringBoolean === true) { | ||
| } | ||
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| declare const someUndefinedCondition: boolean | undefined; | ||
| if (someUndefinedCondition === false) { | ||
| } | ||
| ``` | ||
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| ## Related to | ||
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| - TSLint: [no-boolean-literal-compare](https://palantir.github.io/tslint/rules/no-boolean-literal-compare) |
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packages/eslint-plugin/src/rules/no-unnecessary-boolean-literal-compare.ts
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| import { | ||
| AST_NODE_TYPES, | ||
| TSESTree, | ||
| } from '@typescript-eslint/experimental-utils'; | ||
| import * as tsutils from 'tsutils'; | ||
| import * as ts from 'typescript'; | ||
| import * as util from '../util'; | ||
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| type MessageIds = 'direct' | 'negated'; | ||
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| interface BooleanComparison { | ||
| expression: TSESTree.Expression; | ||
| forTruthy: boolean; | ||
| negated: boolean; | ||
| range: [number, number]; | ||
| } | ||
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| export default util.createRule<[], MessageIds>({ | ||
| name: 'no-unnecessary-boolean-literal-compare', | ||
| meta: { | ||
| docs: { | ||
| description: | ||
| 'Flags unnecessary equality comparisons against boolean literals', | ||
| category: 'Stylistic Issues', | ||
| recommended: false, | ||
| requiresTypeChecking: true, | ||
| }, | ||
| fixable: 'code', | ||
| messages: { | ||
| direct: | ||
| 'This expression unnecessarily compares a boolean value to a boolean instead of using it directly', | ||
| negated: | ||
| 'This expression unnecessarily compares a boolean value to a boolean instead of negating it.', | ||
| }, | ||
| schema: [], | ||
| type: 'suggestion', | ||
| }, | ||
| defaultOptions: [], | ||
| create(context) { | ||
| const parserServices = util.getParserServices(context); | ||
| const checker = parserServices.program.getTypeChecker(); | ||
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| function getBooleanComparison( | ||
| node: TSESTree.BinaryExpression, | ||
| ): BooleanComparison | undefined { | ||
| const comparison = deconstructComparison(node); | ||
| if (!comparison) { | ||
| return undefined; | ||
| } | ||
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| const expressionType = checker.getTypeAtLocation( | ||
| parserServices.esTreeNodeToTSNodeMap.get(comparison.expression), | ||
| ); | ||
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| if ( | ||
| !tsutils.isTypeFlagSet( | ||
| expressionType, | ||
| ts.TypeFlags.Boolean | ts.TypeFlags.BooleanLiteral, | ||
| ) | ||
| ) { | ||
| return undefined; | ||
| } | ||
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| return comparison; | ||
| } | ||
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| function deconstructComparison( | ||
| node: TSESTree.BinaryExpression, | ||
| ): BooleanComparison | undefined { | ||
| const comparisonType = util.getEqualsKind(node.operator); | ||
| if (!comparisonType) { | ||
| return undefined; | ||
| } | ||
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| for (const [against, expression] of [ | ||
| [node.right, node.left], | ||
| [node.left, node.right], | ||
| ]) { | ||
| if ( | ||
| against.type !== AST_NODE_TYPES.Literal || | ||
| typeof against.value !== 'boolean' | ||
| ) { | ||
| continue; | ||
| } | ||
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| const { value } = against; | ||
| const negated = node.operator.startsWith('!'); | ||
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| return { | ||
| forTruthy: value ? !negated : negated, | ||
| expression, | ||
| negated, | ||
| range: | ||
| expression.range[0] < against.range[0] | ||
| ? [expression.range[1], against.range[1]] | ||
| : [against.range[1], expression.range[1]], | ||
| }; | ||
| } | ||
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| return undefined; | ||
| } | ||
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| return { | ||
| BinaryExpression(node): void { | ||
| const comparison = getBooleanComparison(node); | ||
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| if (comparison) { | ||
| context.report({ | ||
| fix: function*(fixer) { | ||
| yield fixer.removeRange(comparison.range); | ||
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| if (!comparison.forTruthy) { | ||
| yield fixer.insertTextBefore(node, '!'); | ||
| } | ||
| }, | ||
| messageId: comparison.negated ? 'negated' : 'direct', | ||
| node, | ||
| }); | ||
| } | ||
| }, | ||
| }; | ||
| }, | ||
| }); |
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106
packages/eslint-plugin/tests/rules/no-unnecessary-boolean-literal-compare.test.ts
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| import rule from '../../src/rules/no-unnecessary-boolean-literal-compare'; | ||
| import { RuleTester, getFixturesRootDir } from '../RuleTester'; | ||
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| const rootDir = getFixturesRootDir(); | ||
| const ruleTester = new RuleTester({ | ||
| parser: '@typescript-eslint/parser', | ||
| parserOptions: { | ||
| ecmaVersion: 2015, | ||
| tsconfigRootDir: rootDir, | ||
| project: './tsconfig.json', | ||
| }, | ||
| }); | ||
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| ruleTester.run('boolean-literal-compare', rule, { | ||
| valid: [ | ||
| ` | ||
| declare const varAny: any; | ||
| varAny === true; | ||
| `, | ||
| ` | ||
| declare const varAny: any; | ||
| varAny == false; | ||
| `, | ||
| ` | ||
| declare const varString: string; | ||
| varString === false; | ||
| `, | ||
| ` | ||
| declare const varString: string; | ||
| varString === true; | ||
| `, | ||
| ` | ||
| declare const varObject: {}; | ||
| varObject === true; | ||
| `, | ||
| ` | ||
| declare const varObject: {}; | ||
| varObject == false; | ||
| `, | ||
| ` | ||
| declare const varBooleanOrString: boolean | undefined; | ||
| varBooleanOrString === false; | ||
| `, | ||
| ` | ||
| declare const varBooleanOrString: boolean | undefined; | ||
| varBooleanOrString == true; | ||
| `, | ||
| ` | ||
| declare const varBooleanOrUndefined: boolean | undefined; | ||
| varBooleanOrUndefined === true; | ||
| `, | ||
| `'false' === true;`, | ||
| `'true' === false;`, | ||
| ], | ||
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| invalid: [ | ||
| { | ||
| code: `true === true`, | ||
| errors: [ | ||
| { | ||
| messageId: 'direct', | ||
| }, | ||
| ], | ||
| output: `true`, | ||
| }, | ||
| { | ||
| code: `false !== true`, | ||
| errors: [ | ||
| { | ||
| messageId: 'negated', | ||
| }, | ||
| ], | ||
| output: `!false`, | ||
| }, | ||
| { | ||
| code: ` | ||
| declare const varBoolean: boolean; | ||
| if (varBoolean !== false) { } | ||
| `, | ||
| errors: [ | ||
| { | ||
| messageId: 'negated', | ||
| }, | ||
| ], | ||
| output: ` | ||
| declare const varBoolean: boolean; | ||
| if (varBoolean) { } | ||
| `, | ||
| }, | ||
| { | ||
| code: ` | ||
| declare const varTrue: true; | ||
| if (varTrue !== true) { } | ||
| `, | ||
| errors: [ | ||
| { | ||
| messageId: 'negated', | ||
| }, | ||
| ], | ||
| output: ` | ||
| declare const varTrue: true; | ||
| if (!varTrue) { } | ||
| `, | ||
| }, | ||
| ], | ||
| }); |