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