1 | /**
|
2 | * @fileoverview Rule to flag fall-through cases in switch statements.
|
3 | * @author Matt DuVall <http://mattduvall.com/>
|
4 | */
|
5 | ;
|
6 |
|
7 | //------------------------------------------------------------------------------
|
8 | // Requirements
|
9 | //------------------------------------------------------------------------------
|
10 |
|
11 | const lodash = require("lodash");
|
12 |
|
13 | //------------------------------------------------------------------------------
|
14 | // Helpers
|
15 | //------------------------------------------------------------------------------
|
16 |
|
17 | const DEFAULT_FALLTHROUGH_COMMENT = /falls?\s?through/iu;
|
18 |
|
19 | /**
|
20 | * Checks whether or not a given node has a fallthrough comment.
|
21 | * @param {ASTNode} node A SwitchCase node to get comments.
|
22 | * @param {RuleContext} context A rule context which stores comments.
|
23 | * @param {RegExp} fallthroughCommentPattern A pattern to match comment to.
|
24 | * @returns {boolean} `true` if the node has a valid fallthrough comment.
|
25 | */
|
26 | function hasFallthroughComment(node, context, fallthroughCommentPattern) {
|
27 | const sourceCode = context.getSourceCode();
|
28 | const comment = lodash.last(sourceCode.getCommentsBefore(node));
|
29 |
|
30 | return Boolean(comment && fallthroughCommentPattern.test(comment.value));
|
31 | }
|
32 |
|
33 | /**
|
34 | * Checks whether or not a given code path segment is reachable.
|
35 | * @param {CodePathSegment} segment A CodePathSegment to check.
|
36 | * @returns {boolean} `true` if the segment is reachable.
|
37 | */
|
38 | function isReachable(segment) {
|
39 | return segment.reachable;
|
40 | }
|
41 |
|
42 | /**
|
43 | * Checks whether a node and a token are separated by blank lines
|
44 | * @param {ASTNode} node The node to check
|
45 | * @param {Token} token The token to compare against
|
46 | * @returns {boolean} `true` if there are blank lines between node and token
|
47 | */
|
48 | function hasBlankLinesBetween(node, token) {
|
49 | return token.loc.start.line > node.loc.end.line + 1;
|
50 | }
|
51 |
|
52 | //------------------------------------------------------------------------------
|
53 | // Rule Definition
|
54 | //------------------------------------------------------------------------------
|
55 |
|
56 | module.exports = {
|
57 | meta: {
|
58 | type: "problem",
|
59 |
|
60 | docs: {
|
61 | description: "disallow fallthrough of `case` statements",
|
62 | category: "Best Practices",
|
63 | recommended: true,
|
64 | url: "https://eslint.org/docs/rules/no-fallthrough"
|
65 | },
|
66 |
|
67 | schema: [
|
68 | {
|
69 | type: "object",
|
70 | properties: {
|
71 | commentPattern: {
|
72 | type: "string",
|
73 | default: ""
|
74 | }
|
75 | },
|
76 | additionalProperties: false
|
77 | }
|
78 | ],
|
79 | messages: {
|
80 | case: "Expected a 'break' statement before 'case'.",
|
81 | default: "Expected a 'break' statement before 'default'."
|
82 | }
|
83 | },
|
84 |
|
85 | create(context) {
|
86 | const options = context.options[0] || {};
|
87 | let currentCodePath = null;
|
88 | const sourceCode = context.getSourceCode();
|
89 |
|
90 | /*
|
91 | * We need to use leading comments of the next SwitchCase node because
|
92 | * trailing comments is wrong if semicolons are omitted.
|
93 | */
|
94 | let fallthroughCase = null;
|
95 | let fallthroughCommentPattern = null;
|
96 |
|
97 | if (options.commentPattern) {
|
98 | fallthroughCommentPattern = new RegExp(options.commentPattern, "u");
|
99 | } else {
|
100 | fallthroughCommentPattern = DEFAULT_FALLTHROUGH_COMMENT;
|
101 | }
|
102 |
|
103 | return {
|
104 | onCodePathStart(codePath) {
|
105 | currentCodePath = codePath;
|
106 | },
|
107 | onCodePathEnd() {
|
108 | currentCodePath = currentCodePath.upper;
|
109 | },
|
110 |
|
111 | SwitchCase(node) {
|
112 |
|
113 | /*
|
114 | * Checks whether or not there is a fallthrough comment.
|
115 | * And reports the previous fallthrough node if that does not exist.
|
116 | */
|
117 | if (fallthroughCase && !hasFallthroughComment(node, context, fallthroughCommentPattern)) {
|
118 | context.report({
|
119 | messageId: node.test ? "case" : "default",
|
120 | node
|
121 | });
|
122 | }
|
123 | fallthroughCase = null;
|
124 | },
|
125 |
|
126 | "SwitchCase:exit"(node) {
|
127 | const nextToken = sourceCode.getTokenAfter(node);
|
128 |
|
129 | /*
|
130 | * `reachable` meant fall through because statements preceded by
|
131 | * `break`, `return`, or `throw` are unreachable.
|
132 | * And allows empty cases and the last case.
|
133 | */
|
134 | if (currentCodePath.currentSegments.some(isReachable) &&
|
135 | (node.consequent.length > 0 || hasBlankLinesBetween(node, nextToken)) &&
|
136 | lodash.last(node.parent.cases) !== node) {
|
137 | fallthroughCase = node;
|
138 | }
|
139 | }
|
140 | };
|
141 | }
|
142 | };
|