eslint/lib/rules/no-lonely-if.js

   1 /**
   2  * @fileoverview Rule to disallow if as the only statement in an else block
   3  * @author Brandon Mills
   4  */
   5 "use strict";
   6
   7 //------------------------------------------------------------------------------
   8 // Rule Definition
   9 //------------------------------------------------------------------------------
  10
  11 /** @type {import('../shared/types').Rule} */
  12 module.exports = {
  13     meta: {
  14         type: "suggestion",
  15
  16         docs: {
  17             description: "Disallow `if` statements as the only statement in `else` blocks",
  18             recommended: false,
  19             url: "https://eslint.org/docs/latest/rules/no-lonely-if"
  20         },
  21
  22         schema: [],
  23         fixable: "code",
  24
  25         messages: {
  26             unexpectedLonelyIf: "Unexpected if as the only statement in an else block."
  27         }
  28     },
  29
  30     create(context) {
  31         const sourceCode = context.sourceCode;
  32
  33         return {
  34             IfStatement(node) {
  35                 const parent = node.parent,
  36                     grandparent = parent.parent;
  37
  38                 if (parent && parent.type === "BlockStatement" &&
  39                         parent.body.length === 1 && grandparent &&
  40                         grandparent.type === "IfStatement" &&
  41                         parent === grandparent.alternate) {
  42                     context.report({
  43                         node,
  44                         messageId: "unexpectedLonelyIf",
  45                         fix(fixer) {
  46                             const openingElseCurly = sourceCode.getFirstToken(parent);
  47                             const closingElseCurly = sourceCode.getLastToken(parent);
  48                             const elseKeyword = sourceCode.getTokenBefore(openingElseCurly);
  49                             const tokenAfterElseBlock = sourceCode.getTokenAfter(closingElseCurly);
  50                             const lastIfToken = sourceCode.getLastToken(node.consequent);
  51                             const sourceText = sourceCode.getText();
  52
  53                             if (sourceText.slice(openingElseCurly.range[1],
  54                                 node.range[0]).trim() || sourceText.slice(node.range[1], closingElseCurly.range[0]).trim()) {
  55
  56                                 // Don't fix if there are any non-whitespace characters interfering (e.g. comments)
  57                                 return null;
  58                             }
  59
  60                             if (
  61                                 node.consequent.type !== "BlockStatement" && lastIfToken.value !== ";" && tokenAfterElseBlock &&
  62                                 (
  63                                     node.consequent.loc.end.line === tokenAfterElseBlock.loc.start.line ||
  64                                     /^[([/+`-]/u.test(tokenAfterElseBlock.value) ||
  65                                     lastIfToken.value === "++" ||
  66                                     lastIfToken.value === "--"
  67                                 )
  68                             ) {
  69
  70                                 /*
  71                                  * If the `if` statement has no block, and is not followed by a semicolon, make sure that fixing
  72                                  * the issue would not change semantics due to ASI. If this would happen, don't do a fix.
  73                                  */
  74                                 return null;
  75                             }
  76
  77                             return fixer.replaceTextRange(
  78                                 [openingElseCurly.range[0], closingElseCurly.range[1]],
  79                                 (elseKeyword.range[1] === openingElseCurly.range[0] ? " " : "") + sourceCode.getText(node)
  80                             );
  81                         }
  82                     });
  83                 }
  84             }
  85         };
  86
  87     }
  88 };