import/extensions should have a ignorePackages option. Fixes #414

docs/rules/extensions.md

@@ -6,7 +6,7 @@ In order to provide a consistent use of file extensions across your code base, t
 
 ## Rule Details
 
-This rule either takes one string option, one object option, or a string and an object option. If it is the string `"never"` (the default value), then the rule forbids the use for any extension. If it is the string `"always"`, then the rule enforces the use of extensions for all import statements.
+This rule either takes one string option, one object option, or a string and an object option. If it is the string `"never"` (the default value), then the rule forbids the use for any extension. If it is the string `"always"`, then the rule enforces the use of extensions for all import statements. If it is the string `"ignorePackages"`, then the rule enforces the use of extensions for all import statements except package imports.
 
 By providing an object you can configure each extension separately, so for example `{ "js": "always", "json": "never" }` would always enforce the use of the `.js` extension but never allow the use of the `.json` extension.
 
@@ -86,6 +86,30 @@ import express from 'express/index.js';
 import * as path from 'path';
 ```
 
+The following patterns are considered problems when configuration set to "ignorePackages":
+
+```js
+import foo from './foo';
+
+import bar from './bar';
+
+import Component from './Component'
+
+```
+
+The following patterns are not considered problems when configuration set to "ignorePackages":
+
+```js
+import foo from './foo.js';
+
+import bar from './bar.json';
+
+import Component from './Component.jsx'
+
+import express from 'express';
+
+```
+
 ## When Not To Use It
 
 If you are not concerned about a consistent usage of file extension.

src/core/importType.js

@@ -23,7 +23,7 @@ function isExternalPath(path, name, settings) {
 }
 
 const externalModuleRegExp = /^\w/
-function isExternalModule(name, settings, path) {
+export function isExternalModule(name, settings, path) {
   return externalModuleRegExp.test(name) && isExternalPath(path, name, settings)
 }
 

src/rules/extensions.js

@@ -2,9 +2,9 @@ import path from 'path'
 import has from 'has'
 
 import resolve from 'eslint-module-utils/resolve'
-import { isBuiltIn } from '../core/importType'
+import { isBuiltIn, isExternalModule } from '../core/importType'
 
-const enumValues = { enum: [ 'always', 'never' ] }
+const enumValues = { enum: [ 'always', 'ignorePackages', 'never' ] }
 const patternProperties = {
   type: 'object',
   patternProperties: { '.*': enumValues },
@@ -46,9 +46,10 @@ module.exports = {
       typeof configuration === 'object' ? configuration : context.options[1]
     )
 
-    function isUseOfExtensionRequired(extension) {
+    function isUseOfExtensionRequired(extension, isModule) {
       if (!has(modifiers, extension)) { modifiers[extension] = defaultConfig }
-      return modifiers[extension] === 'always'
+      const modifier = modifiers[extension];
+      return (!isModule && modifier === 'ignorePackages') || modifier === 'always';
     }
 
     function isUseOfExtensionForbidden(extension) {
@@ -77,8 +78,11 @@ module.exports = {
       // for unresolved, use source value.
       const extension = path.extname(resolvedPath || importPath).substring(1)
 
+      // determine if this is a module
+      const isModule = isExternalModule(importPath, context.settings);
+
       if (!extension || !importPath.endsWith(extension)) {
-        if (isUseOfExtensionRequired(extension) && !isUseOfExtensionForbidden(extension)) {
+        if (isUseOfExtensionRequired(extension, isModule) && !isUseOfExtensionForbidden(extension)) {
           context.report({
             node: source,
             message: