--- /dev/null
+/**
+ * @fileoverview Rule to flag the generator functions that does not have yield.
+ * @author Toru Nagashima
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+ meta: {
+ type: "suggestion",
+
+ docs: {
+ description: "require generator functions to contain `yield`",
+ category: "ECMAScript 6",
+ recommended: true,
+ url: "https://eslint.org/docs/rules/require-yield"
+ },
+
+ schema: []
+ },
+
+ create(context) {
+ const stack = [];
+
+ /**
+ * If the node is a generator function, start counting `yield` keywords.
+ * @param {Node} node A function node to check.
+ * @returns {void}
+ */
+ function beginChecking(node) {
+ if (node.generator) {
+ stack.push(0);
+ }
+ }
+
+ /**
+ * If the node is a generator function, end counting `yield` keywords, then
+ * reports result.
+ * @param {Node} node A function node to check.
+ * @returns {void}
+ */
+ function endChecking(node) {
+ if (!node.generator) {
+ return;
+ }
+
+ const countYield = stack.pop();
+
+ if (countYield === 0 && node.body.body.length > 0) {
+ context.report({ node, message: "This generator function does not have 'yield'." });
+ }
+ }
+
+ return {
+ FunctionDeclaration: beginChecking,
+ "FunctionDeclaration:exit": endChecking,
+ FunctionExpression: beginChecking,
+ "FunctionExpression:exit": endChecking,
+
+ // Increases the count of `yield` keyword.
+ YieldExpression() {
+
+ /* istanbul ignore else */
+ if (stack.length > 0) {
+ stack[stack.length - 1] += 1;
+ }
+ }
+ };
+ }
+};