--- /dev/null
+/**
+ * @fileoverview Rule to flag use of an lexical declarations inside a case clause
+ * @author Erik Arvidsson
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+ meta: {
+ type: "suggestion",
+
+ docs: {
+ description: "disallow lexical declarations in case clauses",
+ category: "Best Practices",
+ recommended: true,
+ url: "https://eslint.org/docs/rules/no-case-declarations"
+ },
+
+ schema: [],
+
+ messages: {
+ unexpected: "Unexpected lexical declaration in case block."
+ }
+ },
+
+ create(context) {
+
+ /**
+ * Checks whether or not a node is a lexical declaration.
+ * @param {ASTNode} node A direct child statement of a switch case.
+ * @returns {boolean} Whether or not the node is a lexical declaration.
+ */
+ function isLexicalDeclaration(node) {
+ switch (node.type) {
+ case "FunctionDeclaration":
+ case "ClassDeclaration":
+ return true;
+ case "VariableDeclaration":
+ return node.kind !== "var";
+ default:
+ return false;
+ }
+ }
+
+ return {
+ SwitchCase(node) {
+ for (let i = 0; i < node.consequent.length; i++) {
+ const statement = node.consequent[i];
+
+ if (isLexicalDeclaration(statement)) {
+ context.report({
+ node: statement,
+ messageId: "unexpected"
+ });
+ }
+ }
+ }
+ };
+
+ }
+};