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/**
* @fileoverview Rule to flag fall-through cases in switch statements.
* @author Matt DuVall <http://mattduvall.com/>
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const lodash = require("lodash");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
const DEFAULT_FALLTHROUGH_COMMENT = /falls?\s?through/iu;
/**
* Checks whether or not a given node has a fallthrough comment.
* @param {ASTNode} node A SwitchCase node to get comments.
* @param {RuleContext} context A rule context which stores comments.
* @param {RegExp} fallthroughCommentPattern A pattern to match comment to.
* @returns {boolean} `true` if the node has a valid fallthrough comment.
*/
function hasFallthroughComment(node, context, fallthroughCommentPattern) {
const sourceCode = context.getSourceCode();
const comment = lodash.last(sourceCode.getCommentsBefore(node));
return Boolean(comment && fallthroughCommentPattern.test(comment.value));
}
/**
* Checks whether or not a given code path segment is reachable.
* @param {CodePathSegment} segment A CodePathSegment to check.
* @returns {boolean} `true` if the segment is reachable.
*/
function isReachable(segment) {
return segment.reachable;
}
/**
* Checks whether a node and a token are separated by blank lines
* @param {ASTNode} node The node to check
* @param {Token} token The token to compare against
* @returns {boolean} `true` if there are blank lines between node and token
*/
function hasBlankLinesBetween(node, token) {
return token.loc.start.line > node.loc.end.line + 1;
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
type: "problem",
docs: {
description: "disallow fallthrough of `case` statements",
category: "Best Practices",
recommended: true,
url: "https://eslint.org/docs/rules/no-fallthrough"
},
schema: [
{
type: "object",
properties: {
commentPattern: {
type: "string",
default: ""
}
},
additionalProperties: false
}
],
messages: {
case: "Expected a 'break' statement before 'case'.",
default: "Expected a 'break' statement before 'default'."
}
},
create(context) {
const options = context.options[0] || {};
let currentCodePath = null;
const sourceCode = context.getSourceCode();
/*
* We need to use leading comments of the next SwitchCase node because
* trailing comments is wrong if semicolons are omitted.
*/
let fallthroughCase = null;
let fallthroughCommentPattern = null;
if (options.commentPattern) {
fallthroughCommentPattern = new RegExp(options.commentPattern, "u");
} else {
fallthroughCommentPattern = DEFAULT_FALLTHROUGH_COMMENT;
}
return {
onCodePathStart(codePath) {
currentCodePath = codePath;
},
onCodePathEnd() {
currentCodePath = currentCodePath.upper;
},
SwitchCase(node) {
/*
* Checks whether or not there is a fallthrough comment.
* And reports the previous fallthrough node if that does not exist.
*/
if (fallthroughCase && !hasFallthroughComment(node, context, fallthroughCommentPattern)) {
context.report({
messageId: node.test ? "case" : "default",
node
});
}
fallthroughCase = null;
},
"SwitchCase:exit"(node) {
const nextToken = sourceCode.getTokenAfter(node);
/*
* `reachable` meant fall through because statements preceded by
* `break`, `return`, or `throw` are unreachable.
* And allows empty cases and the last case.
*/
if (currentCodePath.currentSegments.some(isReachable) &&
(node.consequent.length > 0 || hasBlankLinesBetween(node, nextToken)) &&
lodash.last(node.parent.cases) !== node) {
fallthroughCase = node;
}
}
};
}
};
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