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 +1,95 @@
+/**
+ * @fileoverview Rule to flag updates of imported bindings.
+ * @author Toru Nagashima <https://github.com/mysticatea>
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Check if the identifier node is placed at to update members.
+ * @param {ASTNode} id The Identifier node to check.
+ * @returns {boolean} `true` if the member of `id` was updated.
+ */
+function isMemberUpdate(id) {
+    const parent = id.parent;
+    const grandparent = parent.parent;
+
+    return (
+        parent.type === "MemberExpression" &&
+        parent.object === id &&
+        (
+            (
+                grandparent.type === "AssignmentExpression" &&
+                grandparent.left === parent
+            ) ||
+            (
+                grandparent.type === "UpdateExpression" &&
+                grandparent.argument === parent
+            ) ||
+            (
+                grandparent.type === "UnaryExpression" &&
+                grandparent.operator === "delete" &&
+                grandparent.argument === parent
+            )
+        )
+    );
+}
+
+//------------------------------------------------------------------------------
+// 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) {
+                for (const variable of context.getDeclaredVariables(node)) {
+                    const shouldCheckMembers = variable.defs.some(
+                        d => d.node.type === "ImportNamespaceSpecifier"
+                    );
+
+                    for (const reference of variable.references) {
+                        const idNode = reference.identifier;
+
+                        if (reference.isWrite()) {
+                            context.report({
+                                node: idNode.parent,
+                                messageId: "readonly",
+                                data: { name: idNode.name }
+                            });
+                        } else if (shouldCheckMembers && isMemberUpdate(idNode)) {
+                            context.report({
+                                node: idNode.parent.parent,
+                                messageId: "readonlyMember",
+                                data: { name: idNode.name }
+                            });
+                        }
+                    }
+                }
+            }
+        };
+
+    }
+};

tests/lib/rules/no-import-assign.js

@@ -0,0 +1,104 @@
+/**
+ * @fileoverview Tests for no-import-assign rule.
+ * @author Toru Nagashima <https://github.com/mysticatea>
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const rule = require("../../../lib/rules/no-import-assign"),
+    { RuleTester } = require("../../../lib/rule-tester");
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+const ruleTester = new RuleTester({
+    parserOptions: {
+        ecmaVersion: 2015,
+        sourceType: "module"
+    }
+});
+
+ruleTester.run("no-import-assign", rule, {
+    valid: [
+        "import mod from 'mod'; mod.prop = 0",
+        "import mod from 'mod'; mod.prop += 0",
+        "import mod from 'mod'; mod.prop++",
+        "import mod from 'mod'; delete mod.prop",
+        "import {named} from 'mod'; named.prop = 0",
+        "import {named} from 'mod'; named.prop += 0",
+        "import {named} from 'mod'; named.prop++",
+        "import {named} from 'mod'; delete named.prop",
+        "import * as mod from 'mod'; mod.named.prop = 0",
+        "import * as mod from 'mod'; mod.named.prop += 0",
+        "import * as mod from 'mod'; mod.named.prop++",
+        "import * as mod from 'mod'; delete mod.named.prop",
+        "import * as mod from 'mod'; obj[mod] = 0",
+        "import * as mod from 'mod'; obj[mod.named] = 0",
+        "import mod from 'mod'; { let mod = 0; mod = 1 }",
+        "import * as mod from 'mod'; { let mod = 0; mod = 1 }",
+        "import {} from 'mod'"
+    ],
+    invalid: [
+        {
+            code: "import mod1 from 'mod'; mod1 = 0",
+            errors: [{ messageId: "readonly", data: { name: "mod1" }, column: 25 }]
+        },
+        {
+            code: "import mod2 from 'mod'; mod2 += 0",
+            errors: [{ messageId: "readonly", data: { name: "mod2" }, column: 25 }]
+        },
+        {
+            code: "import mod3 from 'mod'; mod3++",
+            errors: [{ messageId: "readonly", data: { name: "mod3" }, column: 25 }]
+        },
+        {
+            code: "import {named1} from 'mod'; named1 = 0",
+            errors: [{ messageId: "readonly", data: { name: "named1" }, column: 29 }]
+        },
+        {
+            code: "import {named2} from 'mod'; named2 += 0",
+            errors: [{ messageId: "readonly", data: { name: "named2" }, column: 29 }]
+        },
+        {
+            code: "import {named3} from 'mod'; named3++",
+            errors: [{ messageId: "readonly", data: { name: "named3" }, column: 29 }]
+        },
+        {
+            code: "import {named4 as foo} from 'mod'; foo = 0; named4 = 0",
+            errors: [{ messageId: "readonly", data: { name: "foo" }, column: 36 }]
+        },
+        {
+            code: "import * as mod1 from 'mod'; mod1 = 0",
+            errors: [{ messageId: "readonly", data: { name: "mod1" }, column: 30 }]
+        },
+        {
+            code: "import * as mod2 from 'mod'; mod2 += 0",
+            errors: [{ messageId: "readonly", data: { name: "mod2" }, column: 30 }]
+        },
+        {
+            code: "import * as mod3 from 'mod'; mod3++",
+            errors: [{ messageId: "readonly", data: { name: "mod3" }, column: 30 }]
+        },
+        {
+            code: "import * as mod4 from 'mod'; mod4.named = 0",
+            errors: [{ messageId: "readonlyMember", data: { name: "mod4" }, column: 30 }]
+        },
+        {
+            code: "import * as mod5 from 'mod'; mod5.named += 0",
+            errors: [{ messageId: "readonlyMember", data: { name: "mod5" }, column: 30 }]
+        },
+        {
+            code: "import * as mod6 from 'mod'; mod6.named++",
+            errors: [{ messageId: "readonlyMember", data: { name: "mod6" }, column: 30 }]
+        },
+        {
+            code: "import * as mod7 from 'mod'; delete mod7.named",
+            errors: [{ messageId: "readonlyMember", data: { name: "mod7" }, column: 30 }]
+        }
+    ]
+});

tools/rule-types.json

@@ -119,6 +119,7 @@
     "no-implicit-coercion": "suggestion",
     "no-implicit-globals": "suggestion",
     "no-implied-eval": "suggestion",
+    "no-import-assign": "problem",
     "no-inline-comments": "suggestion",
     "no-inner-declarations": "problem",
     "no-invalid-regexp": "problem",