no-lonely-if.js
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/**
* @fileoverview Rule to disallow if as the only statement in an else block
* @author Brandon Mills
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../shared/types').Rule} */
module.exports = {
meta: {
type: "suggestion",
docs: {
description: "Disallow `if` statements as the only statement in `else` blocks",
recommended: false,
url: "https://eslint.org/docs/rules/no-lonely-if"
},
schema: [],
fixable: "code",
messages: {
unexpectedLonelyIf: "Unexpected if as the only statement in an else block."
}
},
create(context) {
const sourceCode = context.getSourceCode();
return {
IfStatement(node) {
const ancestors = context.getAncestors(),
parent = ancestors.pop(),
grandparent = ancestors.pop();
if (parent && parent.type === "BlockStatement" &&
parent.body.length === 1 && grandparent &&
grandparent.type === "IfStatement" &&
parent === grandparent.alternate) {
context.report({
node,
messageId: "unexpectedLonelyIf",
fix(fixer) {
const openingElseCurly = sourceCode.getFirstToken(parent);
const closingElseCurly = sourceCode.getLastToken(parent);
const elseKeyword = sourceCode.getTokenBefore(openingElseCurly);
const tokenAfterElseBlock = sourceCode.getTokenAfter(closingElseCurly);
const lastIfToken = sourceCode.getLastToken(node.consequent);
const sourceText = sourceCode.getText();
if (sourceText.slice(openingElseCurly.range[1],
node.range[0]).trim() || sourceText.slice(node.range[1], closingElseCurly.range[0]).trim()) {
// Don't fix if there are any non-whitespace characters interfering (e.g. comments)
return null;
}
if (
node.consequent.type !== "BlockStatement" && lastIfToken.value !== ";" && tokenAfterElseBlock &&
(
node.consequent.loc.end.line === tokenAfterElseBlock.loc.start.line ||
/^[([/+`-]/u.test(tokenAfterElseBlock.value) ||
lastIfToken.value === "++" ||
lastIfToken.value === "--"
)
) {
/*
* If the `if` statement has no block, and is not followed by a semicolon, make sure that fixing
* the issue would not change semantics due to ASI. If this would happen, don't do a fix.
*/
return null;
}
return fixer.replaceTextRange(
[openingElseCurly.range[0], closingElseCurly.range[1]],
(elseKeyword.range[1] === openingElseCurly.range[0] ? " " : "") + sourceCode.getText(node)
);
}
});
}
}
};
}
};