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Add no-boolean-literal-compare rule
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,14 @@ | ||
| --- | ||
| ruleName: no-boolean-compare | ||
| description: 'Warns on comparison to a boolean literal, as in `x === true`.' | ||
| hasFix: true | ||
| optionsDescription: Not configurable. | ||
| options: null | ||
| optionExamples: | ||
| - 'true' | ||
| type: style | ||
| typescriptOnly: true | ||
| layout: rule | ||
| title: 'Rule: no-boolean-compare' | ||
| optionsJSON: 'null' | ||
| --- |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,15 @@ | ||
| --- | ||
| ruleName: no-boolean-literal-compare | ||
| description: 'Warns on comparison to a boolean literal, as in `x === true`.' | ||
| hasFix: true | ||
| optionsDescription: Not configurable. | ||
| options: null | ||
| optionExamples: | ||
| - 'true' | ||
| type: style | ||
| typescriptOnly: true | ||
| requiresTypeInfo: true | ||
| layout: rule | ||
| title: 'Rule: no-boolean-literal-compare' | ||
| optionsJSON: 'null' | ||
| --- |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,131 @@ | ||
| /** | ||
| * @license | ||
| * Copyright 2017 Palantir Technologies, Inc. | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
|
|
||
| import * as ts from "typescript"; | ||
|
|
||
| import * as Lint from "../index"; | ||
|
|
||
| export class Rule extends Lint.Rules.TypedRule { | ||
| /* tslint:disable:object-literal-sort-keys */ | ||
| public static metadata: Lint.IRuleMetadata = { | ||
| ruleName: "no-boolean-literal-compare", | ||
| description: "Warns on comparison to a boolean literal, as in `x === true`.", | ||
| hasFix: true, | ||
| optionsDescription: "Not configurable.", | ||
| options: null, | ||
| optionExamples: ["true"], | ||
| type: "style", | ||
| typescriptOnly: true, | ||
| requiresTypeInfo: true, | ||
| }; | ||
| /* tslint:enable:object-literal-sort-keys */ | ||
|
|
||
| public static FAILURE_STRING(negate: boolean) { | ||
| return `This expression is unnecessarily compared to a boolean. Just ${negate ? "negate it" : "use it directly"}.`; | ||
| } | ||
|
|
||
| public applyWithProgram(sourceFile: ts.SourceFile, langSvc: ts.LanguageService): Lint.RuleFailure[] { | ||
| return this.applyWithWalker(new Walker(sourceFile, this.getOptions(), langSvc.getProgram())); | ||
| } | ||
| } | ||
|
|
||
| class Walker extends Lint.ProgramAwareRuleWalker { | ||
| public visitBinaryExpression(node: ts.BinaryExpression) { | ||
| this.check(node); | ||
| super.visitBinaryExpression(node); | ||
| } | ||
|
|
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| private check(node: ts.BinaryExpression) { | ||
| const comparison = deconstructComparison(node); | ||
| if (comparison === undefined) { | ||
| return; | ||
| } | ||
|
|
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| const { negate, expression } = comparison; | ||
| const type = this.getTypeChecker().getTypeAtLocation(expression); | ||
| if (!Lint.isTypeFlagSet(type, ts.TypeFlags.Boolean)) { | ||
| return; | ||
| } | ||
|
|
||
| const deleted = node.left === expression | ||
| ? this.deleteFromTo(node.left.end, node.end) | ||
| : this.deleteFromTo(node.getStart(), node.right.getStart()); | ||
| const replacements = [deleted]; | ||
| if (negate) { | ||
| if (needsParenthesesForNegate(expression)) { | ||
| replacements.push(this.appendText(node.getStart(), "!(")); | ||
| replacements.push(this.appendText(node.getEnd(), ")")); | ||
| } else { | ||
| replacements.push(this.appendText(node.getStart(), "!")); | ||
| } | ||
| } | ||
|
|
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| this.addFailureAtNode(expression, Rule.FAILURE_STRING(negate), this.createFix(...replacements)); | ||
| } | ||
| } | ||
|
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| function needsParenthesesForNegate(node: ts.Expression) { | ||
| switch (node.kind) { | ||
| case ts.SyntaxKind.AsExpression: | ||
| case ts.SyntaxKind.BinaryExpression: | ||
| return true; | ||
| default: | ||
| return false; | ||
| } | ||
| } | ||
|
|
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| function deconstructComparison(node: ts.BinaryExpression): { negate: boolean, expression: ts.Expression } | undefined { | ||
| const { left, operatorToken, right } = node; | ||
| const operator = operatorKind(operatorToken); | ||
| if (operator === undefined) { | ||
| return undefined; | ||
| } | ||
|
|
||
| const leftValue = booleanFromExpression(left); | ||
| if (leftValue !== undefined) { | ||
| return { negate: leftValue !== operator, expression: right }; | ||
| } | ||
| const rightValue = booleanFromExpression(right); | ||
| if (rightValue !== undefined) { | ||
| return { negate: rightValue !== operator, expression: left }; | ||
| } | ||
| return undefined; | ||
| } | ||
|
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| function operatorKind(operatorToken: ts.BinaryOperatorToken): boolean | undefined { | ||
| switch (operatorToken.kind) { | ||
| case ts.SyntaxKind.EqualsEqualsToken: | ||
| case ts.SyntaxKind.EqualsEqualsEqualsToken: | ||
| return true; | ||
| case ts.SyntaxKind.ExclamationEqualsToken: | ||
| case ts.SyntaxKind.ExclamationEqualsEqualsToken: | ||
| return false; | ||
| default: | ||
| return undefined; | ||
| } | ||
| } | ||
|
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| function booleanFromExpression(node: ts.Expression): boolean | undefined { | ||
| switch (node.kind) { | ||
| case ts.SyntaxKind.TrueKeyword: | ||
| return true; | ||
| case ts.SyntaxKind.FalseKeyword: | ||
| return false; | ||
| default: | ||
| return undefined; | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,30 @@ | ||
| declare const x: boolean; | ||
|
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| x; | ||
| x; | ||
|
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| !x; | ||
| !x; | ||
|
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| !x; | ||
| !x; | ||
|
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| x; | ||
| x; | ||
|
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| x; | ||
|
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| declare const y: boolean | undefined; | ||
| y === true; | ||
|
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| declare function f(): boolean; | ||
| !f(); | ||
|
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| declare const a: number, b: number; | ||
|
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| !(a as any as boolean); | ||
|
|
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| !(a < b); | ||
|
|
||
| !!x; | ||
|
|
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is there a more reliable way to check?
ternary?
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I can't think of a better way to do this, unfortunately.
A ternary operator wouldn't happen here since it
===binds more tightly, so the ternary would have to be parenthesized already anyway.