Merge branch 'no-mutable-exports': merges + closes #290

CHANGELOG.md

@@ -8,6 +8,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 - [`newline-after-import`], new rule. ([#245], thanks [@singles])
 - Added an `optionalDependencies` option to [`no-extraneous-dependencies`] to allow/forbid optional dependencies ([#266], thanks [@jfmengels]).
 - Added `newlines-between` option to [`order`] rule ([#298], thanks [@singles])
+- add [`no-mutable-exports`] rule ([#290], thanks [@josh])
 
 ### Fixed
 - [`extensions`]: fallback to source path for extension enforcement if imported
@@ -194,9 +195,11 @@ for info on changes for earlier releases.
 [`order`]: ./docs/rules/order.md
 [`named`]: ./docs/rules/named.md
 [`newline-after-import`]: ./docs/rules/newline-after-import.md
+[`no-mutable-exports`]: ./docs/rules/no-mutable-exports.md
 
 [#298]: https://github.com/benmosher/eslint-plugin-import/pull/298
 [#296]: https://github.com/benmosher/eslint-plugin-import/pull/296
+[#290]: https://github.com/benmosher/eslint-plugin-import/pull/290
 [#289]: https://github.com/benmosher/eslint-plugin-import/pull/289
 [#288]: https://github.com/benmosher/eslint-plugin-import/pull/288
 [#287]: https://github.com/benmosher/eslint-plugin-import/pull/287
@@ -263,3 +266,4 @@ for info on changes for earlier releases.
 [@taion]: https://github.com/taion
 [@strawbrary]: https://github.com/strawbrary
 [@SimenB]: https://github.com/SimenB
+[@josh]: https://github.com/josh

README.md

@@ -36,6 +36,7 @@ This plugin intends to support linting of ES2015+ (ES6+) import/export syntax, a
 [`no-named-as-default-member`]: ./docs/rules/no-named-as-default-member.md
 [`no-deprecated`]: ./docs/rules/no-deprecated.md
 [`no-extraneous-dependencies`]: ./docs/rules/no-extraneous-dependencies.md
+[`no-mutable-exports`]: ./docs/rules/no-mutable-exports.md
 
 **Module systems:**
 

docs/rules/no-mutable-exports.md

@@ -0,0 +1,52 @@
+# no-mutable-exports
+
+Forbids the use of mutable exports with `var` or `let`.
+
+## Rule Details
+
+Valid:
+
+```js
+export const count = 1
+export function getCount() {}
+export class Counter {}
+```
+
+...whereas here exports will be reported:
+
+```js
+export let count = 2
+export var count = 3
+
+let count = 4
+export { count } // reported here
+```
+
+## Functions/Classes
+
+Note that exported function/class declaration identifiers may be reassigned,
+but are not flagged by this rule at this time. They may be in the future, if a
+reassignment is detected, i.e.
+
+```js
+// possible future behavior!
+export class Counter {} // reported here: exported class is reassigned on line [x].
+Counter = KitchenSink // not reported here unless you enable no-class-assign
+
+// this pre-declaration reassignment is valid on account of function hoisting
+getCount = function getDuke() {} // not reported here without no-func-assign
+export function getCount() {} // reported here: exported function is reassigned on line [x].
+```
+
+To prevent general reassignment of these identifiers, exported or not, you may
+want to enable the following core ESLint rules:
+
+- [no-func-assign]
+- [no-class-assign]
+
+[no-func-assign]: http://eslint.org/docs/rules/no-func-assign
+[no-class-assign]: http://eslint.org/docs/rules/no-class-assign
+
+## When Not To Use It
+
+If your environment correctly implements mutable export bindings.

src/index.js

@@ -5,6 +5,7 @@ export const rules = {
   'namespace': require('./rules/namespace'),
   'no-namespace': require('./rules/no-namespace'),
   'export': require('./rules/export'),
+  'no-mutable-exports': require('./rules/no-mutable-exports'),
   'extensions': require('./rules/extensions'),
 
   'no-named-as-default': require('./rules/no-named-as-default'),

src/rules/no-mutable-exports.js

@@ -0,0 +1,45 @@
+module.exports = function (context) {
+  function checkDeclaration(node) {
+    const {kind} = node
+    if (kind === 'var' || kind === 'let') {
+      context.report(node, `Exporting mutable '${kind}' binding, use 'const' instead.`)
+    }
+  }
+
+  function checkDeclarationsInScope({variables}, name) {
+    for (let variable of variables) {
+      if (variable.name === name) {
+        for (let def of variable.defs) {
+          if (def.type === 'Variable') {
+            checkDeclaration(def.parent)
+          }
+        }
+      }
+    }
+  }
+
+  function handleExportDefault(node) {
+    const scope = context.getScope()
+
+    if (node.declaration.name) {
+      checkDeclarationsInScope(scope, node.declaration.name)
+    }
+  }
+
+  function handleExportNamed(node) {
+    const scope = context.getScope()
+
+    if (node.declaration)  {
+      checkDeclaration(node.declaration)
+    } else {
+      for (let specifier of node.specifiers) {
+        checkDeclarationsInScope(scope, specifier.local.name)
+      }
+    }
+  }
+
+  return {
+    'ExportDefaultDeclaration': handleExportDefault,
+    'ExportNamedDeclaration': handleExportNamed,
+  }
+}

tests/src/rules/no-mutable-exports.js

@@ -0,0 +1,62 @@
+import {test} from '../utils'
+import {RuleTester} from 'eslint'
+import rule from 'rules/no-mutable-exports'
+
+const ruleTester = new RuleTester()
+
+ruleTester.run('no-mutable-exports', rule, {
+  valid: [
+    test({ code: 'export const count = 1'}),
+    test({ code: 'export function getCount() {}'}),
+    test({ code: 'export class Counter {}'}),
+    test({ code: 'export default count = 1'}),
+    test({ code: 'export default function getCount() {}'}),
+    test({ code: 'export default class Counter {}'}),
+    test({ code: 'const count = 1\nexport { count }'}),
+    test({ code: 'const count = 1\nexport { count as counter }'}),
+    test({ code: 'const count = 1\nexport default count'}),
+    test({ code: 'const count = 1\nexport { count as default }'}),
+    test({ code: 'function getCount() {}\nexport { getCount }'}),
+    test({ code: 'function getCount() {}\nexport { getCount as getCounter }'}),
+    test({ code: 'function getCount() {}\nexport default getCount'}),
+    test({ code: 'function getCount() {}\nexport { getCount as default }'}),
+    test({ code: 'class Counter {}\nexport { Counter }'}),
+    test({ code: 'class Counter {}\nexport { Counter as Count }'}),
+    test({ code: 'class Counter {}\nexport default Counter'}),
+    test({ code: 'class Counter {}\nexport { Counter as default }'}),
+  ],
+  invalid: [
+    test({
+      code: 'export let count = 1',
+      errors: ['Exporting mutable \'let\' binding, use \'const\' instead.'],
+    }),
+    test({
+      code: 'export var count = 1',
+      errors: ['Exporting mutable \'var\' binding, use \'const\' instead.'],
+    }),
+    test({
+      code: 'let count = 1\nexport { count }',
+      errors: ['Exporting mutable \'let\' binding, use \'const\' instead.'],
+    }),
+    test({
+      code: 'var count = 1\nexport { count }',
+      errors: ['Exporting mutable \'var\' binding, use \'const\' instead.'],
+    }),
+    test({
+      code: 'let count = 1\nexport { count as counter }',
+      errors: ['Exporting mutable \'let\' binding, use \'const\' instead.'],
+    }),
+    test({
+      code: 'var count = 1\nexport { count as counter }',
+      errors: ['Exporting mutable \'var\' binding, use \'const\' instead.'],
+    }),
+    test({
+      code: 'let count = 1\nexport default count',
+      errors: ['Exporting mutable \'let\' binding, use \'const\' instead.'],
+    }),
+    test({
+      code: 'var count = 1\nexport default count',
+      errors: ['Exporting mutable \'var\' binding, use \'const\' instead.'],
+    }),
+  ],
+})