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qwen/nodejs/node_modules/eslint/lib/rules/no-fallthrough.js

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+/**
+ * @fileoverview Rule to flag fall-through cases in switch statements.
+ * @author Matt DuVall <http://mattduvall.com/>
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const { directivesPattern } = require("../shared/directives");
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+const DEFAULT_FALLTHROUGH_COMMENT = /falls?\s?through/iu;
+
+/**
+ * Checks all segments in a set and returns true if any are reachable.
+ * @param {Set<CodePathSegment>} segments The segments to check.
+ * @returns {boolean} True if any segment is reachable; false otherwise.
+ */
+function isAnySegmentReachable(segments) {
+
+    for (const segment of segments) {
+        if (segment.reachable) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+/**
+ * Checks whether or not a given comment string is really a fallthrough comment and not an ESLint directive.
+ * @param {string} comment The comment string to check.
+ * @param {RegExp} fallthroughCommentPattern The regular expression used for checking for fallthrough comments.
+ * @returns {boolean} `true` if the comment string is truly a fallthrough comment.
+ */
+function isFallThroughComment(comment, fallthroughCommentPattern) {
+    return fallthroughCommentPattern.test(comment) && !directivesPattern.test(comment.trim());
+}
+
+/**
+ * Checks whether or not a given case has a fallthrough comment.
+ * @param {ASTNode} caseWhichFallsThrough SwitchCase node which falls through.
+ * @param {ASTNode} subsequentCase The case after caseWhichFallsThrough.
+ * @param {RuleContext} context A rule context which stores comments.
+ * @param {RegExp} fallthroughCommentPattern A pattern to match comment to.
+ * @returns {boolean} `true` if the case has a valid fallthrough comment.
+ */
+function hasFallthroughComment(caseWhichFallsThrough, subsequentCase, context, fallthroughCommentPattern) {
+    const sourceCode = context.sourceCode;
+
+    if (caseWhichFallsThrough.consequent.length === 1 && caseWhichFallsThrough.consequent[0].type === "BlockStatement") {
+        const trailingCloseBrace = sourceCode.getLastToken(caseWhichFallsThrough.consequent[0]);
+        const commentInBlock = sourceCode.getCommentsBefore(trailingCloseBrace).pop();
+
+        if (commentInBlock && isFallThroughComment(commentInBlock.value, fallthroughCommentPattern)) {
+            return true;
+        }
+    }
+
+    const comment = sourceCode.getCommentsBefore(subsequentCase).pop();
+
+    return Boolean(comment && isFallThroughComment(comment.value, fallthroughCommentPattern));
+}
+
+/**
+ * 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
+//------------------------------------------------------------------------------
+
+/** @type {import('../shared/types').Rule} */
+module.exports = {
+    meta: {
+        type: "problem",
+
+        docs: {
+            description: "Disallow fallthrough of `case` statements",
+            recommended: true,
+            url: "https://eslint.org/docs/latest/rules/no-fallthrough"
+        },
+
+        schema: [
+            {
+                type: "object",
+                properties: {
+                    commentPattern: {
+                        type: "string",
+                        default: ""
+                    },
+                    allowEmptyCase: {
+                        type: "boolean",
+                        default: false
+                    }
+                },
+                additionalProperties: false
+            }
+        ],
+        messages: {
+            case: "Expected a 'break' statement before 'case'.",
+            default: "Expected a 'break' statement before 'default'."
+        }
+    },
+
+    create(context) {
+        const options = context.options[0] || {};
+        const codePathSegments = [];
+        let currentCodePathSegments = new Set();
+        const sourceCode = context.sourceCode;
+        const allowEmptyCase = options.allowEmptyCase || false;
+
+        /*
+         * 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() {
+                codePathSegments.push(currentCodePathSegments);
+                currentCodePathSegments = new Set();
+            },
+
+            onCodePathEnd() {
+                currentCodePathSegments = codePathSegments.pop();
+            },
+
+            onUnreachableCodePathSegmentStart(segment) {
+                currentCodePathSegments.add(segment);
+            },
+
+            onUnreachableCodePathSegmentEnd(segment) {
+                currentCodePathSegments.delete(segment);
+            },
+
+            onCodePathSegmentStart(segment) {
+                currentCodePathSegments.add(segment);
+            },
+
+            onCodePathSegmentEnd(segment) {
+                currentCodePathSegments.delete(segment);
+            },
+
+
+            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(fallthroughCase, 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 (isAnySegmentReachable(currentCodePathSegments) &&
+                    (node.consequent.length > 0 || (!allowEmptyCase && hasBlankLinesBetween(node, nextToken))) &&
+                    node.parent.cases[node.parent.cases.length - 1] !== node) {
+                    fallthroughCase = node;
+                }
+            }
+        };
+    }
+};