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noTautologyExpressionRule.ts
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noTautologyExpressionRule.ts
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/**
* @license
* Copyright 2013 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 tsutils from "tsutils";
import * as ts from "typescript";
import * as Lint from "../index";
const TAUTOLOGY_DISCOVERED_ERROR_STRING =
"Expression is either a tautology or a contradiction. Binary expression is redundant.";
export class Rule extends Lint.Rules.AbstractRule {
public static metadata: Lint.IRuleMetadata = {
description: Lint.Utils.dedent`
Enforces that relational/equality binary operators does not take two equal variables/literals as operands.
Expression like 3 === 3, someVar === someVar, "1" > "1" are either a tautology or contradiction, and will produce an error.
`,
optionExamples: [true],
options: null,
optionsDescription: "Not configurable.",
rationale: `Clean redundant code and unnecessary comparison of objects and literals.`,
ruleName: "no-tautology-expression",
type: "functionality",
typescriptOnly: false,
};
public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
return this.applyWithFunction(sourceFile, walk);
}
}
function walk(context: Lint.WalkContext<void>) {
const cb = (node: ts.Node): void => {
if (
tsutils.isBinaryExpression(node) &&
isRelationalOrOrLogicalOperator(node.operatorToken)
) {
if (isLiteral(node.left) && isLiteral(node.right)) {
if (node.left.text === node.right.text) {
context.addFailureAtNode(node, TAUTOLOGY_DISCOVERED_ERROR_STRING);
}
} else if (
tsutils.isPropertyAccessExpression(node.left) &&
tsutils.isPropertyAccessExpression(node.right)
) {
if (node.left.name.text === node.right.name.text) {
context.addFailureAtNode(node, TAUTOLOGY_DISCOVERED_ERROR_STRING);
}
}
}
return ts.forEachChild(node, cb);
};
return ts.forEachChild(context.sourceFile, cb);
}
function isLiteral(node: ts.Node): node is ts.StringLiteral | ts.NumericLiteral {
return (node as ts.StringLiteral) !== undefined || (node as ts.NumericLiteral) !== undefined;
}
function isRelationalOrOrLogicalOperator(operator: ts.BinaryOperatorToken): boolean {
return new Set([
ts.SyntaxKind.LessThanToken,
ts.SyntaxKind.GreaterThanToken,
ts.SyntaxKind.LessThanEqualsToken,
ts.SyntaxKind.GreaterThanEqualsToken,
ts.SyntaxKind.EqualsEqualsToken,
ts.SyntaxKind.EqualsEqualsEqualsToken,
ts.SyntaxKind.ExclamationEqualsToken,
ts.SyntaxKind.ExclamationEqualsEqualsToken,
ts.SyntaxKind.AmpersandAmpersandToken,
ts.SyntaxKind.BarBarToken,
]).has(operator.kind);
}