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Add 'binary-expression-operand-order' rule (palantir#2805)
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/** | ||
* @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. | ||
*/ | ||
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import { isBinaryExpression } from "tsutils"; | ||
import * as ts from "typescript"; | ||
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import * as Lint from "../index"; | ||
import { isNegativeNumberLiteral } from "../language/utils"; | ||
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export class Rule extends Lint.Rules.AbstractRule { | ||
/* tslint:disable:object-literal-sort-keys */ | ||
public static metadata: Lint.IRuleMetadata = { | ||
ruleName: "binary-expression-operand-order", | ||
description: Lint.Utils.dedent` | ||
In a binary expression, a literal should always be on the right-hand side if possible. | ||
For example, prefer 'x + 1' over '1 + x'.`, | ||
optionsDescription: "Not configurable.", | ||
options: null, | ||
optionExamples: [true], | ||
type: "style", | ||
typescriptOnly: false, | ||
}; | ||
/* tslint:enable:object-literal-sort-keys */ | ||
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public static FAILURE_STRING = "Literal expression should be on the right-hand side of a binary expression."; | ||
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public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] { | ||
return this.applyWithFunction(sourceFile, walk); | ||
} | ||
} | ||
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function walk(ctx: Lint.WalkContext<void>): void { | ||
ts.forEachChild(ctx.sourceFile, function cb(node) { | ||
if (isBinaryExpression(node) && isLiteral(node.left) && !isAllowedOrderedOperator(node)) { | ||
ctx.addFailureAtNode(node, Rule.FAILURE_STRING); | ||
} | ||
ts.forEachChild(node, cb); | ||
}); | ||
} | ||
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/** Allows certain inherently ordered operators that can't easily be written with the literal on the right. */ | ||
function isAllowedOrderedOperator(node: ts.BinaryExpression): boolean { | ||
switch (node.operatorToken.kind) { | ||
case ts.SyntaxKind.PlusToken: | ||
// Allow `"foo" + x` but not `1 + x`. | ||
return node.left.kind === ts.SyntaxKind.StringLiteral; | ||
case ts.SyntaxKind.MinusToken: | ||
case ts.SyntaxKind.SlashToken: | ||
case ts.SyntaxKind.PercentToken: | ||
case ts.SyntaxKind.LessThanLessThanToken: | ||
case ts.SyntaxKind.GreaterThanGreaterThanToken: | ||
case ts.SyntaxKind.GreaterThanGreaterThanGreaterThanToken: | ||
case ts.SyntaxKind.AsteriskAsteriskToken: | ||
case ts.SyntaxKind.InKeyword: | ||
case ts.SyntaxKind.CommaToken: | ||
return true; | ||
default: | ||
return false; | ||
} | ||
} | ||
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function isLiteral(node: ts.Expression): boolean { | ||
switch (node.kind) { | ||
case ts.SyntaxKind.StringLiteral: | ||
case ts.SyntaxKind.NumericLiteral: | ||
case ts.SyntaxKind.TrueKeyword: | ||
case ts.SyntaxKind.FalseKeyword: | ||
case ts.SyntaxKind.NullKeyword: | ||
return true; | ||
case ts.SyntaxKind.Identifier: | ||
return (node as ts.Identifier).originalKeywordKind === ts.SyntaxKind.UndefinedKeyword; | ||
case ts.SyntaxKind.PrefixUnaryExpression: | ||
return isNegativeNumberLiteral(node); | ||
case ts.SyntaxKind.ParenthesizedExpression: | ||
return isLiteral((node as ts.ParenthesizedExpression).expression); | ||
default: | ||
return false; | ||
} | ||
} |
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"red" !== x; | ||
~~~~~~~~~~~ [0] | ||
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true === x; | ||
~~~~~~~~~~ [0] | ||
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false === x; | ||
~~~~~~~~~~~ [0] | ||
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null == x; | ||
~~~~~~~~~ [0] | ||
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undefined != x; | ||
~~~~~~~~~~~~~~ [0] | ||
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5 < x; | ||
~~~~~ [0] | ||
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-1 + x; | ||
~~~~~~ [0] | ||
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(-1) + x; | ||
~~~~~~~~ [0] | ||
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// Allows string literal left hand side. | ||
"foo" + x; | ||
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// Allows certain ordered operators. | ||
1 - x; | ||
1 / x; | ||
1 % x; | ||
1 << x; | ||
1 >> x; | ||
1 >>> x; | ||
2 ** x; | ||
"key" in x; | ||
"foo", x; | ||
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[0]: Literal expression should be on the right-hand side of a binary expression. |
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{ | ||
"rules": { | ||
"binary-expression-operand-order": true | ||
} | ||
} |