[New] prefer-default-export: add "target" option

Fixes #2600.

Author: azyzz228

CHANGELOG.md

@@ -17,6 +17,7 @@ This change log adheres to standards from [Keep a CHANGELOG](https://keepachange
 - [`order`]: new `alphabetize.orderImportKind` option to sort imports with same path based on their kind (`type`, `typeof`) ([#2544], thanks [@stropho])
 - [`consistent-type-specifier-style`]: add rule ([#2473], thanks [@bradzacher])
 - Add [`no-empty-named-blocks`] rule ([#2568], thanks [@guilhermelimak])
+- [`prefer-default-export`]: add "target" option ([#2602], thanks [@azyzz228])
 
 ### Fixed
 - [`order`]: move nested imports closer to main import entry ([#2396], thanks [@pri1311])
@@ -1025,6 +1026,7 @@ for info on changes for earlier releases.
 [`memo-parser`]: ./memo-parser/README.md
 
 [#2605]: https://github.com/import-js/eslint-plugin-import/pull/2605
+[#2602]: https://github.com/import-js/eslint-plugin-import/pull/2602
 [#2598]: https://github.com/import-js/eslint-plugin-import/pull/2598
 [#2589]: https://github.com/import-js/eslint-plugin-import/pull/2589
 [#2588]: https://github.com/import-js/eslint-plugin-import/pull/2588

README.md

@@ -89,7 +89,7 @@ This plugin intends to support linting of ES2015+ (ES6+) import/export syntax, a
 | [no-namespace](docs/rules/no-namespace.md)                                       | Forbid namespace (a.k.a. "wildcard" `*`) imports.                          |    |       |    | 🔧 |    |    |
 | [no-unassigned-import](docs/rules/no-unassigned-import.md)                       | Forbid unassigned imports                                                  |    |       |    |    |    |    |
 | [order](docs/rules/order.md)                                                     | Enforce a convention in module import order.                               |    |       |    | 🔧 |    |    |
-| [prefer-default-export](docs/rules/prefer-default-export.md)                     | Prefer a default export if module exports a single name.                   |    |       |    |    |    |    |
+| [prefer-default-export](docs/rules/prefer-default-export.md)                     | Prefer a default export if module exports a single name or multiple names. |    |       |    |    |    |    |
 
 <!-- end auto-generated rules list -->
 

docs/rules/prefer-default-export.md

@@ -2,10 +2,44 @@
 
 <!-- end auto-generated rule header -->
 
-When there is only a single export from a module, prefer using default export over named export.
+In exporting files, this rule checks if there is default export or not.
 
 ## Rule Details
 
+##### rule schema:
+
+```javascript
+"import/prefer-default-export": [
+    ( "off" | "warn" | "error" ),
+	{ "target": "single" | "any" } // default is "single"
+]
+```
+
+### Config Options
+
+There are two options available: `single` and `any`. By default, if you do not specify the option, rule will assume it is `single`.
+
+#### single
+
+**Definition**: When there is only a single export from a module, prefer using default export over named export.
+
+How to setup config file for this rule:
+
+```javascript
+// you can manually specify it
+"rules": {
+    "import/prefer-default-export": [
+        ( "off" | "warn" | "error" ),
+        { "target": "single" }
+    ]
+}
+
+// config setup below will also work
+"rules": {
+    "import/prefer-default-export": "off" | "warn" | "error"
+}
+```
+
 The following patterns are considered warnings:
 
 ```javascript
@@ -58,3 +92,95 @@ export { foo as default }
 // Any batch export will disable this rule. The remote module is not inspected.
 export * from './other-module'
 ```
+
+#### any
+
+**Definition**: any exporting file must contain a default export.
+
+How to setup config file for this rule:
+
+```javascript
+// you have to manually specify it
+"rules": {
+    "import/prefer-default-export": [
+        ( "off" | "warn" | "error" ),
+        { "target": "any" }
+    ]
+}
+```
+
+
+The following patterns are *not* considered warnings:
+
+```javascript
+// good1.js
+
+//has default export
+export default function bar() {};
+```
+
+```javascript
+// good2.js
+
+// has default export
+let foo;
+export { foo as default }
+```
+
+```javascript
+// good3.js
+
+//contains multiple exports AND default export
+export const a = 5;
+export function bar(){};
+let foo;
+export { foo as default }
+```
+
+```javascript
+// good4.js
+
+// does not contain any exports => file is not checked by the rule
+import * as foo from './foo';
+```
+
+```javascript
+// export-star.js
+
+// Any batch export will disable this rule. The remote module is not inspected.
+export * from './other-module'
+```
+
+The following patterns are considered warnings:
+
+```javascript
+// bad1.js
+
+//has 2 named exports, but no default export
+export const foo = 'foo';
+export const bar = 'bar';
+```
+
+```javascript
+// bad2.js
+
+// does not have default export
+let foo, bar;
+export { foo, bar }
+```
+
+```javascript
+// bad3.js
+
+// does not have default export
+export { a, b } from "foo.js"
+```
+
+```javascript
+// bad4.js
+
+// does not have default export
+let item;
+export const foo = item;
+export { item };
+```

src/rules/prefer-default-export.js

@@ -2,15 +2,28 @@
 
 import docsUrl from '../docsUrl';
 
+const SINGLE_EXPORT_ERROR_MESSAGE = 'Prefer default export on a file with single export.';
+const ANY_EXPORT_ERROR_MESSAGE = 'Prefer default export to be present on every file that has export.';
+
 module.exports = {
   meta: {
     type: 'suggestion',
     docs: {
       category: 'Style guide',
-      description: 'Prefer a default export if module exports a single name.',
+      description: 'Prefer a default export if module exports a single name or multiple names.',
       url: docsUrl('prefer-default-export'),
     },
-    schema: [],
+    schema: [{
+      type: 'object',
+      properties:{
+        target: {
+          type: 'string',
+          enum: ['single', 'any'],
+          default: 'single',
+        },
+      },
+      additionalProperties: false,
+    }],
   },
 
   create(context) {
@@ -19,7 +32,8 @@ module.exports = {
     let hasStarExport = false;
     let hasTypeExport = false;
     let namedExportNode = null;
-
+    // get options. by default we look into files with single export
+    const { target = 'single' } =  context.options[0] || {};
     function captureDeclaration(identifierOrPattern) {
       if (identifierOrPattern && identifierOrPattern.type === 'ObjectPattern') {
         // recursively capture
@@ -88,8 +102,13 @@ module.exports = {
       },
 
       'Program:exit': function () {
-        if (specifierExportCount === 1 && !hasDefaultExport && !hasStarExport && !hasTypeExport) {
-          context.report(namedExportNode, 'Prefer default export.');
+        if (hasDefaultExport || hasStarExport || hasTypeExport) {
+          return;
+        }
+        if (target === 'single' && specifierExportCount === 1) {
+          context.report(namedExportNode, SINGLE_EXPORT_ERROR_MESSAGE);
+        } else if (target === 'any' && specifierExportCount > 0) {
+          context.report(namedExportNode, ANY_EXPORT_ERROR_MESSAGE);
         }
       },
     };