no-extraneous-dependencies includes only paths that can be resolved,

as only resolved paths can be reliably tested if they live in a `node_modules` folder.

Up until now, this rule assumed, that every package that lives in a `node_modules` folder
or *cannot be resolved* is an external package.
This happens because of [that line](https://github.com/benmosher/eslint-plugin-import/blob/master/src/core/importType.js#L32).

If project uses aliasing, or transforms imports, this assumption is wrong,
as they may not be resolvable by import plugin, but also, they should not be defined in package.json.

Changing `isExternalPath` will make any ordering lints unstable
(order may change depending if you ran `npm install` or not).

Using `import/ignore` setting does not make sense too, as it's used to ignore imports unknown to the plugin,
like .css files. But still, you may import a css file from a dependency, and this rule should check that.

docs/rules/no-extraneous-dependencies.md

@@ -3,6 +3,8 @@
 Forbid the import of external modules that are not declared in the `package.json`'s `dependencies`, `devDependencies`, `optionalDependencies` or `peerDependencies`.
 The closest parent `package.json` will be used. If no `package.json` is found, the rule will not lint anything. This behaviour can be changed with the rule option `packageDir`.
 
+Modules have to be installed for this rule to work.
+
 ### Options
 
 This rule supports the following options:

src/rules/no-extraneous-dependencies.js

@@ -2,6 +2,7 @@ import path from 'path'
 import fs from 'fs'
 import readPkgUp from 'read-pkg-up'
 import minimatch from 'minimatch'
+import resolve from 'eslint-module-utils/resolve'
 import importType from '../core/importType'
 import isStaticRequire from '../core/staticRequire'
 
@@ -57,6 +58,10 @@ function reportIfMissing(context, deps, depsOptions, node, name) {
   if (importType(name, context) !== 'external') {
     return
   }
+  const resolved = resolve(name, context)
+  if (!resolved) {
+    return
+  }
   const splitName = name.split('/')
   const packageName = splitName[0][0] === '@'
     ? splitName.slice(0, 2).join('/')

tests/files/package.json

@@ -8,7 +8,7 @@
     "eslint": "2.x"
   },
   "dependencies": {
-    "@scope/core": "^1.0.0",
+    "@org/package": "^1.0.0",
     "jquery": "^3.1.0",
     "lodash.cond": "^4.3.0",
     "pkg-up": "^1.0.0"

tests/src/rules/no-extraneous-dependencies.js

@@ -30,7 +30,7 @@ ruleTester.run('no-extraneous-dependencies', rule, {
     test({ code: 'import "fs"'}),
     test({ code: 'import "./foo"'}),
     test({ code: 'import "lodash.isarray"'}),
-    test({ code: 'import "@scope/core"'}),
+    test({ code: 'import "@org/package"'}),
 
     test({ code: 'import "electron"', settings: { 'import/core-modules': ['electron'] } }),
     test({ code: 'import "eslint"' }),
@@ -57,7 +57,7 @@ ruleTester.run('no-extraneous-dependencies', rule, {
     test({
       code: 'import chai from "chai"',
       options: [{devDependencies: ['*.test.js', '*.spec.js']}],
-      filename: 'foo.spec.js',
+      filename: path.join(process.cwd(), 'foo.spec.js'),
     }),
     test({
       code: 'import chai from "chai"',
@@ -79,17 +79,17 @@ ruleTester.run('no-extraneous-dependencies', rule, {
       }],
     }),
     test({
-      code: 'var donthaveit = require("@scope/donthaveit")',
+      code: 'var donthaveit = require("@org/not-a-dependency")',
       errors: [{
         ruleId: 'no-extraneous-dependencies',
-        message: '\'@scope/donthaveit\' should be listed in the project\'s dependencies. Run \'npm i -S @scope/donthaveit\' to add it',
+        message: '\'@org/not-a-dependency\' should be listed in the project\'s dependencies. Run \'npm i -S @org/not-a-dependency\' to add it',
       }],
     }),
     test({
-      code: 'var donthaveit = require("@scope/donthaveit/lib/foo")',
+      code: 'var donthaveit = require("@org/not-a-dependency/foo")',
       errors: [{
         ruleId: 'no-extraneous-dependencies',
-        message: '\'@scope/donthaveit\' should be listed in the project\'s dependencies. Run \'npm i -S @scope/donthaveit\' to add it',
+        message: '\'@org/not-a-dependency\' should be listed in the project\'s dependencies. Run \'npm i -S @org/not-a-dependency\' to add it',
       }],
     }),
     test({