[Fix] make 'import/order' work in a monorepo setup with scoped modules

Fixes import-js#1597

Author: skozin

CHANGELOG.md

@@ -5,6 +5,15 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 This change log adheres to standards from [Keep a CHANGELOG](http://keepachangelog.com).
 
 ## [Unreleased]
+### Fixed
+- [`import/external-module-folders` setting] now correctly works with directories containing
+  modules symlinked from `node_modules` ([#PR])
+
+### Changed
+- [`import/external-module-folders` setting] behavior is more strict now: it will only match
+  complete path segments. That is, `some/path` won't match `/my/awesome/path` but will still
+  match `/my/some/path` and `/my/some/path/index.js`. Also, if an item starts with a forward
+  slash, it will be treated as an absolute path prefix ([#PR])
 
 ## [2.20.0] - 2020-01-10
 ### Added

README.md

@@ -339,7 +339,24 @@ Contribution of more such shared configs for other platforms are welcome!
 
 #### `import/external-module-folders`
 
-An array of folders. Resolved modules only from those folders will be considered as "external". By default - `["node_modules"]`. Makes sense if you have configured your path or webpack to handle your internal paths differently and want to considered modules from some folders, for example `bower_components` or `jspm_modules`, as "external".
+An array of folders. Resolved modules only from those folders will be considered as "external". By default - `["node_modules"]`. Makes sense if you have configured your path or webpack to handle your internal paths differently and want to consider modules from some folders, for example `bower_components` or `jspm_modules`, as "external". This option is also useful in a monorepo setup: list here all
+directories that contain monorepo's packages and they will be treated as external ones no matter
+which resolver is used.
+
+Each item in this array is either a folder's name, its subpath, or its absolute prefix path.
+Examples:
+
+- `jspm_modules` will match any file or folder named `jspm_modules` or which has a direct or
+  non-direct parent named `jspm_modules`, e.g. `/home/me/project/jspm_modules` or
+  `/home/me/project/jspm_modules/some-pkg/index.js`.
+- `packages/core` will match any path that contains these two segments, for example
+  `/home/me/project/packages/core/src/utils.js`.
+- `/home/me/project/packages` will only match files and directories inside this directory,
+  and the directory itself.
+
+Please note that incomplete names are not allowed here so `components` won't match
+`bower_components` and `packages/ui` won't match `packages/ui-utils` (but will match
+`packages/ui/utils`).
 
 #### `import/parsers`
 

src/core/importType.js

@@ -1,5 +1,4 @@
 import coreModules from 'resolve/lib/core'
-import { join } from 'path'
 
 import resolve from 'eslint-module-utils/resolve'
 
@@ -13,7 +12,7 @@ function baseModule(name) {
 }
 
 export function isAbsolute(name) {
-  return name.indexOf('/') === 0
+  return !name || name[0] === '/'
 }
 
 // path is defined only when a resolver resolves to a non-standard path
@@ -26,11 +25,17 @@ export function isBuiltIn(name, settings, path) {
 
 function isExternalPath(path, name, settings) {
   const folders = (settings && settings['import/external-module-folders']) || ['node_modules']
+  return !path || folders.some(folder => isSubpath(folder, path))
+}
 
-  // extract the part before the first / (redux-saga/effects => redux-saga)
-  const packageName = name.match(/([^/]+)/)[0]
+function isSubpath(subpath, path) {
+  const subpathRegExpSrc = escapeRegExp(subpath.replace(/[/]$/, ''))
+  const subpathRegExp = new RegExp(`${isAbsolute(subpath) ? '^' : '(?:^|/)'}${subpathRegExpSrc}(?:/|$)`)
+  return subpathRegExp.test(path)
+}
 
-  return !path || folders.some(folder => -1 < path.indexOf(join(folder, packageName)))
+function escapeRegExp(string) {
+  return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
 }
 
 const externalModuleRegExp = /^\w/