From 4416072124e55d85980d89f30e3915186276f729 Mon Sep 17 00:00:00 2001
From: Sam Kozin <sam.kozin@gmail.com>
Date: Sun, 12 Jan 2020 01:38:32 +0300
Subject: [PATCH] [Fix] make 'import/order' work in a monorepo setup with
 scoped modules

Fixes #1597
---
 CHANGELOG.md           |  9 +++++++++
 README.md              | 19 ++++++++++++++++++-
 src/core/importType.js | 15 ++++++++++-----
 3 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e89efd1bee..1f79c2e61a 100644
--- a/CHANGELOG.md
+++ b/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
diff --git a/README.md b/README.md
index 814d5fc28d..60b5bb1f11 100644
--- a/README.md
+++ b/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`
 
diff --git a/src/core/importType.js b/src/core/importType.js
index 8ec01c29e8..bac8f133b0 100644
--- a/src/core/importType.js
+++ b/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/