Add no-default-export + docs/tests (#936)

CHANGELOG.md

@@ -10,6 +10,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 
 ## [2.8.0] - 2017-10-18
 ### Added
+- [`no-default-export`] rule ([#889], thanks [@isiahmeadows])
 - [`exports-last`] rule ([#620] + [#632], thanks [@k15a])
 
 ### Changed
@@ -435,11 +436,13 @@ for info on changes for earlier releases.
 [`exports-last`]: ./docs/rules/exports-last.md
 [`group-exports`]: ./docs/rules/group-exports.md
 [`no-self-import`]: ./docs/rules/no-self-import.md
+[`no-default-export`]: ./docs/rules/no-default-export.md
 
 [`memo-parser`]: ./memo-parser/README.md
 
 [#944]: https://github.com/benmosher/eslint-plugin-import/pull/944
 [#891]: https://github.com/benmosher/eslint-plugin-import/pull/891
+[#889]: https://github.com/benmosher/eslint-plugin-import/pull/889
 [#858]: https://github.com/benmosher/eslint-plugin-import/pull/858
 [#843]: https://github.com/benmosher/eslint-plugin-import/pull/843
 [#871]: https://github.com/benmosher/eslint-plugin-import/pull/871
@@ -670,3 +673,4 @@ for info on changes for earlier releases.
 [@rosswarren]: https://github.com/rosswarren
 [@alexgorbatchev]: https://github.com/alexgorbatchev
 [@robertrossmann]: https://github.com/robertrossmann
+[@isiahmeadows]: https://github.com/isiahmeadows

docs/rules/no-default-export.md

@@ -0,0 +1,63 @@
+# no-default-export
+
+Prohibit default exports. Mostly an inverse of [`prefer-default-export`].
+
+[`prefer-default-export`]: ./prefer-default-export.md
+
+## Rule Details
+
+The following patterns are considered warnings:
+
+```javascript
+// bad1.js
+
+// There is a default export.
+export const foo = 'foo';
+const bar = 'bar';
+export default 'bar';
+```
+
+```javascript
+// bad2.js
+
+// There is a default export.
+const foo = 'foo';
+export { foo as default }
+```
+
+The following patterns are not warnings:
+
+```javascript
+// good1.js
+
+// There is only a single module export and it's a named export.
+export const foo = 'foo';
+```
+
+```javascript
+// good2.js
+
+// There is more than one named export in the module.
+export const foo = 'foo';
+export const bar = 'bar';
+```
+
+```javascript
+// good3.js
+
+// There is more than one named export in the module
+const foo = 'foo';
+const bar = 'bar';
+export { foo, bar }
+```
+
+```javascript
+// export-star.js
+
+// Any batch export will disable this rule. The remote module is not inspected.
+export * from './other-module'
+```
+
+## When Not To Use It
+
+If you don't care if default imports are used, or if you prefer default imports over named imports.

src/index.js

@@ -29,6 +29,7 @@ export const rules = {
   'order': require('./rules/order'),
   'newline-after-import': require('./rules/newline-after-import'),
   'prefer-default-export': require('./rules/prefer-default-export'),
+  'no-default-export': require('./rules/no-default-export'),
   'no-dynamic-require': require('./rules/no-dynamic-require'),
   'unambiguous': require('./rules/unambiguous'),
   'no-unassigned-import': require('./rules/no-unassigned-import'),

src/rules/no-default-export.js

@@ -0,0 +1,35 @@
+module.exports = {
+  meta: {
+    docs: {},
+  },
+
+  create(context) {
+    // ignore non-modules
+    if (context.parserOptions.sourceType !== 'module') {
+      return {}
+    }
+
+    const preferNamed = 'Prefer named exports.'
+    const noAliasDefault = ({local}) =>
+      `Do not alias \`${local.name}\` as \`default\`. Just export ` +
+      `\`${local.name}\` itself instead.`
+
+    return {
+      ExportDefaultDeclaration(node) {
+        context.report({node, message: preferNamed})
+      },
+
+      ExportNamedDeclaration(node) {
+        node.specifiers.forEach(specifier => {
+          if (specifier.type === 'ExportDefaultSpecifier' &&
+              specifier.exported.name === 'default') {
+            context.report({node, message: preferNamed})
+          } else if (specifier.type === 'ExportSpecifier' &&
+              specifier.exported.name === 'default') {
+            context.report({node, message: noAliasDefault(specifier)})
+          }
+        })
+      },
+    }
+  },
+}

tests/src/rules/no-default-export.js

@@ -0,0 +1,121 @@
+import { test } from '../utils'
+
+import { RuleTester } from 'eslint'
+
+const ruleTester = new RuleTester()
+    , rule = require('rules/no-default-export')
+
+ruleTester.run('no-default-export', rule, {
+  valid: [
+    test({
+      code: `
+        export const foo = 'foo';
+        export const bar = 'bar';
+      `,
+    }),
+    test({
+      code: `
+        export const foo = 'foo';
+        export function bar() {};
+      `,
+    }),
+    test({
+      code: `export const foo = 'foo';`,
+    }),
+    test({
+      code: `
+        const foo = 'foo';
+        export { foo };
+      `,
+    }),
+    test({
+      code: `export { foo, bar }`,
+    }),
+    test({
+      code: `export const { foo, bar } = item;`,
+    }),
+    test({
+      code: `export const { foo, bar: baz } = item;`,
+    }),
+    test({
+      code: `export const { foo: { bar, baz } } = item;`,
+    }),
+    test({
+      code: `
+        export const foo = item;
+        export { item };
+      `,
+    }),
+    test({
+      code: `export * from './foo';`,
+    }),
+    test({
+      code: `export const { foo } = { foo: "bar" };`,
+    }),
+    test({
+      code: `export const { foo: { bar } } = { foo: { bar: "baz" } };`,
+    }),
+    test({
+      code: 'export { a, b } from "foo.js"',
+      parser: 'babel-eslint',
+    }),
+
+    // no exports at all
+    test({
+      code: `import * as foo from './foo';`,
+    }),
+    test({
+      code: `import foo from './foo';`,
+    }),
+    test({
+      code: `import {default as foo} from './foo';`,
+    }),
+
+    test({
+      code: `export type UserId = number;`,
+      parser: 'babel-eslint',
+    }),
+    test({
+      code: 'export foo from "foo.js"',
+      parser: 'babel-eslint',
+    }),
+    test({
+      code: `export Memory, { MemoryValue } from './Memory'`,
+      parser: 'babel-eslint',
+    }),
+  ],
+  invalid: [
+    test({
+      code: 'export default function bar() {};',
+      errors: [{
+        ruleId: 'ExportDefaultDeclaration',
+        message: 'Prefer named exports.',
+      }],
+    }),
+    test({
+      code: `
+        export const foo = 'foo';
+        export default bar;`,
+      errors: [{
+        ruleId: 'ExportDefaultDeclaration',
+        message: 'Prefer named exports.',
+      }],
+    }),
+    test({
+      code: 'export { foo as default }',
+      errors: [{
+        ruleId: 'ExportNamedDeclaration',
+        message: 'Do not alias `foo` as `default`. Just export `foo` itself ' +
+          'instead.',
+      }],
+    }),
+    test({
+      code: 'export default from "foo.js"',
+      parser: 'babel-eslint',
+      errors: [{
+        ruleId: 'ExportNamedDeclaration',
+        message: 'Prefer named exports.',
+      }],
+    }),
+  ],
+})