New: Add no-setter-return rule (fixes #12285)

docs/rules/no-setter-return.md

@@ -0,0 +1,101 @@
+# Disallow returning values from setters (no-setter-return)
+
+Setters cannot return values.
+
+While returning a value from a setter does not produce an error, the returned value is being ignored. Therefore, returning a value from a setter is either unnecessary or a possible error, since the returned value cannot be used.
+
+## Rule Details
+
+This rule disallows returning values from setters and reports `return` statements in setter functions.
+
+Only `return` without a value is allowed, as it's a control flow statement.
+
+This rule checks setters in:
+
+* Object literals.
+* Class declarations and class expressions.
+* Property descriptors in `Object.create`, `Object.defineProperty`, `Object.defineProperties`, and `Reflect.defineProperty` methods of the global objects.
+
+Examples of **incorrect** code for this rule:
+
+```js
+/*eslint no-setter-return: "error"*/
+
+var foo = {
+    set a(value) {
+        this.val = value;
+        return value;
+    }
+};
+
+class Foo {
+    set a(value) {
+        this.val = value * 2;
+        return this.val;
+    }
+}
+
+const Bar = class {
+    static set a(value) {
+        if (value < 0) {
+            this.val = 0;
+            return 0;
+        }
+        this.val = value;
+    }
+};
+
+Object.defineProperty(foo, "bar", {
+    set(value) {
+        if (value < 0) {
+            return false;
+        }
+        this.val = value;
+    }
+});
+```
+
+Examples of **correct** code for this rule:
+
+```js
+/*eslint no-setter-return: "error"*/
+
+var foo = {
+    set a(value) {
+        this.val = value;
+    }
+};
+
+class Foo {
+    set a(value) {
+        this.val = value * 2;
+    }
+}
+
+const Bar = class {
+    static set a(value) {
+        if (value < 0) {
+            this.val = 0;
+            return;
+        }
+        this.val = value;
+    }
+};
+
+Object.defineProperty(foo, "bar", {
+    set(value) {
+        if (value < 0) {
+            throw new Error("Negative value.");
+        }
+        this.val = value;
+    }
+});
+```
+
+## Further Reading
+
+* [MDN setter](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/set)
+
+## Related Rules
+
+* [getter-return](getter-return.md)

lib/rules/index.js

@@ -186,6 +186,7 @@ module.exports = new LazyLoadingRuleMap(Object.entries({
     "no-self-assign": () => require("./no-self-assign"),
     "no-self-compare": () => require("./no-self-compare"),
     "no-sequences": () => require("./no-sequences"),
+    "no-setter-return": () => require("./no-setter-return"),
     "no-shadow": () => require("./no-shadow"),
     "no-shadow-restricted-names": () => require("./no-shadow-restricted-names"),
     "no-spaced-func": () => require("./no-spaced-func"),

lib/rules/no-setter-return.js

@@ -0,0 +1,227 @@
+/**
+ * @fileoverview Rule to disallow returning values from setters
+ * @author Milos Djermanovic
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const astUtils = require("./utils/ast-utils");
+const { findVariable } = require("eslint-utils");
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Determines whether the given identifier node is a reference to a global variable.
+ * @param {ASTNode} node `Identifier` node to check.
+ * @param {Scope} scope Scope to which the node belongs.
+ * @returns {boolean} True if the identifier is a reference to a global variable.
+ */
+function isGlobalReference(node, scope) {
+    const variable = findVariable(scope, node);
+
+    return variable !== null && variable.scope.type === "global" && variable.defs.length === 0;
+}
+
+/**
+ * Determines whether the given node is an argument of the specified global method call, at the given `index` position.
+ * E.g., for given `index === 1`, this function checks for `objectName.methodName(foo, node)`, where objectName is a global variable.
+ * @param {ASTNode} node The node to check.
+ * @param {Scope} scope Scope to which the node belongs.
+ * @param {string} objectName Name of the global object.
+ * @param {string} methodName Name of the method.
+ * @param {number} index The given position.
+ * @returns {boolean} `true` if the node is argument at the given position.
+ */
+function isArgumentOfGlobalMethodCall(node, scope, objectName, methodName, index) {
+    const parent = node.parent;
+
+    return parent.type === "CallExpression" &&
+        parent.arguments[index] === node &&
+        parent.callee.type === "MemberExpression" &&
+        astUtils.getStaticPropertyName(parent.callee) === methodName &&
+        parent.callee.object.type === "Identifier" &&
+        parent.callee.object.name === objectName &&
+        isGlobalReference(parent.callee.object, scope);
+}
+
+/**
+ * Determines whether the given node is used as a property descriptor.
+ * @param {ASTNode} node The node to check.
+ * @param {Scope} scope Scope to which the node belongs.
+ * @returns {boolean} `true` if the node is a property descriptor.
+ */
+function isPropertyDescriptor(node, scope) {
+    if (
+        isArgumentOfGlobalMethodCall(node, scope, "Object", "defineProperty", 2) ||
+        isArgumentOfGlobalMethodCall(node, scope, "Reflect", "defineProperty", 2)
+    ) {
+        return true;
+    }
+
+    const parent = node.parent;
+
+    if (
+        parent.type === "Property" &&
+        parent.value === node
+    ) {
+        const grandparent = parent.parent;
+
+        if (
+            grandparent.type === "ObjectExpression" &&
+            (
+                isArgumentOfGlobalMethodCall(grandparent, scope, "Object", "create", 1) ||
+                isArgumentOfGlobalMethodCall(grandparent, scope, "Object", "defineProperties", 1)
+            )
+        ) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+/**
+ * Determines whether the given function node is used as a setter function.
+ * @param {ASTNode} node The node to check.
+ * @param {Scope} scope Scope to which the node belongs.
+ * @returns {boolean} `true` if the node is a setter.
+ */
+function isSetter(node, scope) {
+    const parent = node.parent;
+
+    if (
+        parent.kind === "set" &&
+        parent.value === node
+    ) {
+
+        // Setter in an object literal or in a class
+        return true;
+    }
+
+    if (
+        parent.type === "Property" &&
+        parent.value === node &&
+        astUtils.getStaticPropertyName(parent) === "set" &&
+        parent.parent.type === "ObjectExpression" &&
+        isPropertyDescriptor(parent.parent, scope)
+    ) {
+
+        // Setter in a property descriptor
+        return true;
+    }
+
+    return false;
+}
+
+/**
+ * Finds function's outer scope.
+ * @param {Scope} scope Function's own scope.
+ * @returns {Scope} Function's outer scope.
+ */
+function getOuterScope(scope) {
+    const upper = scope.upper;
+
+    if (upper.type === "function-expression-name") {
+        return upper.upper;
+    }
+
+    return upper;
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "problem",
+
+        docs: {
+            description: "disallow returning values from setters",
+            category: "Possible Errors",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/no-setter-return"
+        },
+
+        schema: [],
+
+        messages: {
+            returnsValue: "Setter cannot return a value."
+        }
+    },
+
+    create(context) {
+        let funcInfo = null;
+
+        /**
+         * Creates and pushes to the stack a function info object for the given function node.
+         * @param {ASTNode} node The function node.
+         * @returns {void}
+         */
+        function enterFunction(node) {
+            const outerScope = getOuterScope(context.getScope());
+
+            funcInfo = {
+                upper: funcInfo,
+                isSetter: isSetter(node, outerScope)
+            };
+        }
+
+        /**
+         * Pops the current function info object from the stack.
+         * @returns {void}
+         */
+        function exitFunction() {
+            funcInfo = funcInfo.upper;
+        }
+
+        /**
+         * Reports the given node.
+         * @param {ASTNode} node Node to report.
+         * @returns {void}
+         */
+        function report(node) {
+            context.report({ node, messageId: "returnsValue" });
+        }
+
+        return {
+
+            /*
+             * Function declarations cannot be setters, but we still have to track them in the `funcInfo` stack to avoid
+             * false positives, because a ReturnStatement node can belong to a function declaration inside a setter.
+             *
+             * Note: A previously declared function can be referenced and actually used as a setter in a property descriptor,
+             * but that's out of scope for this rule.
+             */
+            FunctionDeclaration: enterFunction,
+            FunctionExpression: enterFunction,
+            ArrowFunctionExpression(node) {
+                enterFunction(node);
+
+                if (funcInfo.isSetter && node.expression) {
+
+                    // { set: foo => bar } property descriptor. Report implicit return 'bar' as the equivalent for a return statement.
+                    report(node.body);
+                }
+            },
+
+            "FunctionDeclaration:exit": exitFunction,
+            "FunctionExpression:exit": exitFunction,
+            "ArrowFunctionExpression:exit": exitFunction,
+
+            ReturnStatement(node) {
+
+                // Global returns (e.g., at the top level of a Node module) don't have `funcInfo`.
+                if (funcInfo && funcInfo.isSetter && node.argument) {
+                    report(node);
+                }
+            }
+        };
+    }
+};