New: add no-import-assign (fixes #12237)

docs/rules/no-import-assign.md

@@ -0,0 +1,44 @@
+# disallow assigning to imported bindings (no-import-assign)
+
+The updates of imported bindings by ES Modules cause runtime errors.
+
+## Rule Details
+
+This rule warns the assignments, increments, and decrements of imported bindings.
+
+Examples of **incorrect** code for this rule:
+
+```js
+/*eslint no-import-assign: "error"*/
+
+import mod, { named } from "./mod.mjs"
+import * as mod_ns from "./mod.mjs"
+
+mod = 1          // ERROR: 'mod' is readonly.
+named = 2        // ERROR: 'named' is readonly.
+mod_ns.named = 3 // ERROR: the members of 'mod_ns' is readonly.
+mod_ns = {}      // ERROR: 'mod_ns' is readonly.
+```
+
+Examples of **correct** code for this rule:
+
+```js
+/*eslint no-import-assign: "error"*/
+
+import mod, { named } from "./mod.mjs"
+import * as mod_ns from "./mod.mjs"
+
+mod.prop = 1
+named.prop = 2
+mod_ns.named.prop = 3
+
+// Known Limitation
+function test(obj) {
+    obj.named = 4 // Not errored because 'obj' is not namespace objects.
+}
+test(mod_ns) // Not errored because it doesn't know that 'test' updates the member of the argument.
+```
+
+## When Not To Use It
+
+If you don't want to be notified about modifying imported bindings, you can disable this rule.

lib/rules/index.js

@@ -132,6 +132,7 @@ module.exports = new LazyLoadingRuleMap(Object.entries({
     "no-implicit-coercion": () => require("./no-implicit-coercion"),
     "no-implicit-globals": () => require("./no-implicit-globals"),
     "no-implied-eval": () => require("./no-implied-eval"),
+    "no-import-assign": () => require("./no-import-assign"),
     "no-inline-comments": () => require("./no-inline-comments"),
     "no-inner-declarations": () => require("./no-inner-declarations"),
     "no-invalid-regexp": () => require("./no-invalid-regexp"),

lib/rules/no-import-assign.js

@@ -0,0 +1,238 @@
+/**
+ * @fileoverview Rule to flag updates of imported bindings.
+ * @author Toru Nagashima <https://github.com/mysticatea>
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+const { findVariable, getPropertyName } = require("eslint-utils");
+
+const MutationMethods = {
+    Object: new Set([
+        "assign", "defineProperties", "defineProperty", "freeze",
+        "setPrototypeOf"
+    ]),
+    Reflect: new Set([
+        "defineProperty", "deleteProperty", "set", "setPrototypeOf"
+    ])
+};
+
+/**
+ * Check if a given node is LHS of an assignment node.
+ * @param {ASTNode} node The node to check.
+ * @returns {boolean} `true` if the node is LHS.
+ */
+function isAssignmentLeft(node) {
+    const { parent } = node;
+
+    return (
+        (
+            parent.type === "AssignmentExpression" &&
+            parent.left === node
+        ) ||
+
+        // Destructuring assignments
+        parent.type === "ArrayPattern" ||
+        (
+            parent.type === "Property" &&
+            parent.value === node &&
+            parent.parent.type === "ObjectPattern"
+        ) ||
+        parent.type === "RestElement" ||
+        (
+            parent.type === "AssignmentPattern" &&
+            parent.left === node
+        )
+    );
+}
+
+/**
+ * Check if a given node is the operand of mutation unary operator.
+ * @param {ASTNode} node The node to check.
+ * @returns {boolean} `true` if the node is the operand of mutation unary operator.
+ */
+function isOperandOfMutationUnaryOperator(node) {
+    const { parent } = node;
+
+    return (
+        (
+            parent.type === "UpdateExpression" &&
+            parent.argument === node
+        ) ||
+        (
+            parent.type === "UnaryExpression" &&
+            parent.operator === "delete" &&
+            parent.argument === node
+        )
+    );
+}
+
+/**
+ * Check if a given node is the iteration variable of `for-in`/`for-of` syntax.
+ * @param {ASTNode} node The node to check.
+ * @returns {boolean} `true` if the node is the iteration variable.
+ */
+function isIterationVariable(node) {
+    const { parent } = node;
+
+    return (
+        (
+            parent.type === "ForInStatement" &&
+            parent.left === node
+        ) ||
+        (
+            parent.type === "ForOfStatement" &&
+            parent.left === node
+        )
+    );
+}
+
+/**
+ * Check if a given node is the iteration variable of `for-in`/`for-of` syntax.
+ * @param {ASTNode} node The node to check.
+ * @param {Scope} scope A `escope.Scope` object to find variable (whichever).
+ * @returns {boolean} `true` if the node is the iteration variable.
+ */
+function isArgumentOfWellKnownMutationFunction(node, scope) {
+    const { parent } = node;
+
+    if (
+        parent.type === "CallExpression" &&
+        parent.arguments[0] === node &&
+        parent.callee.type === "MemberExpression" &&
+        parent.callee.object.type === "Identifier"
+    ) {
+        const { callee } = parent;
+        const { object } = callee;
+
+        if (Object.keys(MutationMethods).includes(object.name)) {
+            const variable = findVariable(scope, object);
+
+            return (
+                variable !== null &&
+                variable.scope.type === "global" &&
+                MutationMethods[object.name].has(getPropertyName(callee, scope))
+            );
+        }
+    }
+
+    return false;
+}
+
+/**
+ * Check if the identifier node is placed at to update members.
+ * @param {ASTNode} id The Identifier node to check.
+ * @param {Scope} scope A `escope.Scope` object to find variable (whichever).
+ * @returns {boolean} `true` if the member of `id` was updated.
+ */
+function isMemberWrite(id, scope) {
+    const { parent } = id;
+
+    return (
+        (
+            parent.type === "MemberExpression" &&
+            parent.object === id &&
+            (
+                isAssignmentLeft(parent) ||
+                isOperandOfMutationUnaryOperator(parent) ||
+                isIterationVariable(parent)
+            )
+        ) ||
+        isArgumentOfWellKnownMutationFunction(id, scope)
+    );
+}
+
+/**
+ * Get the mutation node.
+ * @param {ASTNode} id The Identifier node to get.
+ * @returns {ASTNode} The mutation node.
+ */
+function getWriteNode(id) {
+    let node = id.parent;
+
+    while (
+        node &&
+        node.type !== "AssignmentExpression" &&
+        node.type !== "UpdateExpression" &&
+        node.type !== "UnaryExpression" &&
+        node.type !== "CallExpression" &&
+        node.type !== "ForInStatement" &&
+        node.type !== "ForOfStatement"
+    ) {
+        node = node.parent;
+    }
+
+    return node || id;
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "problem",
+
+        docs: {
+            description: "disallow assigning to imported bindings",
+            category: "Possible Errors",
+            recommended: false,
+            url: "https://eslint.org/docs/rules/no-import-assign"
+        },
+
+        schema: [],
+
+        messages: {
+            readonly: "'{{name}}' is read-only.",
+            readonlyMember: "The members of '{{name}}' are read-only."
+        }
+    },
+
+    create(context) {
+        return {
+            ImportDeclaration(node) {
+                const scope = context.getScope();
+
+                for (const variable of context.getDeclaredVariables(node)) {
+                    const shouldCheckMembers = variable.defs.some(
+                        d => d.node.type === "ImportNamespaceSpecifier"
+                    );
+                    let prevIdNode = null;
+
+                    for (const reference of variable.references) {
+                        const idNode = reference.identifier;
+
+                        /*
+                         * AssignmentPattern (e.g. `[a = 0] = b`) makes two write
+                         * references for the same identifier. This should skip
+                         * the one of the two in order to prevent redundant reports.
+                         */
+                        if (idNode === prevIdNode) {
+                            continue;
+                        }
+                        prevIdNode = idNode;
+
+                        if (reference.isWrite()) {
+                            context.report({
+                                node: getWriteNode(idNode),
+                                messageId: "readonly",
+                                data: { name: idNode.name }
+                            });
+                        } else if (shouldCheckMembers && isMemberWrite(idNode, scope)) {
+                            context.report({
+                                node: getWriteNode(idNode),
+                                messageId: "readonlyMember",
+                                data: { name: idNode.name }
+                            });
+                        }
+                    }
+                }
+            }
+        };
+
+    }
+};