Properly track dev edges on virtual root nodes

If the virtualRoot node has a sourceReference, and that sourceReference
node would get its devDep edges loaded, then the virtualRoot node should
as well.

This caused a very useless ERESOLVE error, which could not be properly
forced away, when installing in a project that had conflicting peer deps
in its dev tree.

Related to: npm/cli#2548

lib/node.js

@@ -733,7 +733,9 @@ class Node {
     // Linked targets that are disconnected from the tree are tops,
     // but don't have a 'path' field, only a 'realpath', because we
     // don't know their canonical location. We don't need their devDeps.
-    if (this.isTop && this.path && !this.sourceReference)
+    const { isTop, path, sourceReference } = this
+    const { isTop: srcTop, path: srcPath } = sourceReference || {}
+    if (isTop && path && (!sourceReference || srcTop && srcPath))
       this[_loadDepType](this.package.devDependencies, 'dev')
 
     const pd = this.package.peerDependencies

test/arborist/build-ideal-tree.js

@@ -1,7 +1,9 @@
-const {relative, basename, resolve} = require('path')
+const {basename, resolve} = require('path')
 const t = require('tap')
 const Arborist = require('../..')
 const fixtures = resolve(__dirname, '../fixtures')
+// load the symbolic links that we depend on
+require(fixtures)
 const registryServer = require('../fixtures/registry-mocks/server.js')
 const {registry, auditResponse} = registryServer
 const npa = require('npm-package-arg')
@@ -31,11 +33,10 @@ const normalizePaths = obj => {
     return new Map([...obj].map(([name, val]) => [name, normalizePaths(val)]))
 
   for (const key in obj) {
-    if (['location', 'path', 'realpath', 'resolved', 'spec'].includes(key)) {
+    if (['location', 'path', 'realpath', 'resolved', 'spec'].includes(key))
       obj[key] = normalizePath(obj[key])
-    } else if (typeof obj[key] === 'object' && obj[key] !== null) {
+    else if (typeof obj[key] === 'object' && obj[key] !== null)
       obj[key] = normalizePaths(obj[key])
-    }
   }
   return obj
 }
@@ -2257,8 +2258,8 @@ t.test('peer dep that needs to be replaced', async t => {
   const path = t.testdir({
     'package.json': JSON.stringify({
       dependencies: {
-        "@pmmmwh/react-refresh-webpack-plugin": "^0.4.3",
-        "webpack-dev-server": "^3.11.0"
+        '@pmmmwh/react-refresh-webpack-plugin': '^0.4.3',
+        'webpack-dev-server': '^3.11.0',
       },
     }),
   })
@@ -2270,11 +2271,11 @@ t.test('peer dep override with dep sets being replaced', async t => {
   // that has a peer dependency on webpack 4, it overrides but otherwise fails.
   const path = t.testdir({
     'package.json': JSON.stringify({
-      "devDependencies": {
-        "webpack": "5.0.0",
-        "webpack-dev-server": "3.11.0"
-      }
-    })
+      devDependencies: {
+        webpack: '5.0.0',
+        'webpack-dev-server': '3.11.0',
+      },
+    }),
   })
   await t.rejects(printIdeal(path), { code: 'ERESOLVE' })
   t.matchSnapshot(await printIdeal(path, { force: true }))
@@ -2324,3 +2325,33 @@ t.test('do not fail if root peerDep looser than meta peerDep', async t => {
   const path = resolve(fixtures, 'test-peer-looser-than-dev')
   t.matchSnapshot(await printIdeal(path))
 })
+
+t.test('set the current on ERESOLVE triggered by devDeps', async t => {
+  // fixes a bug where the dev deps are not loaded properly in the
+  // virtual root, leading to incomprehensible ERESOLVE explanations
+  const path = t.testdir({
+    'package.json': JSON.stringify({
+      name: 'root-dev-peer-conflict',
+      version: '1.0.0',
+      devDependencies: {
+        eslint: '^4.19.1',
+        'eslint-config-standard': '^11.0.0',
+      },
+    }),
+  })
+
+  const arb = new Arborist({ path, ...OPT })
+  t.rejects(arb.buildIdealTree(), {
+    code: 'ERESOLVE',
+    current: {
+      name: 'eslint',
+      version: '4.19.1',
+      whileInstalling: {
+        name: 'root-dev-peer-conflict',
+        version: '1.0.0',
+        path: resolve(path),
+      },
+      location: 'node_modules/eslint',
+    },
+  })
+})

test/node.js

@@ -2147,3 +2147,19 @@ t.test('isProjectRoot shows if the node is the root link target', async t => {
   t.equal(link.isRoot, true)
   t.equal(n.isRoot, false)
 })
+
+t.test('virtual references to root node has devDep edges', async t => {
+  const root = new Node({
+    path: '/some/project/path',
+    pkg: {
+      devDependencies: {
+        a: '1',
+      },
+    },
+  })
+  const virtualRoot = new Node({
+    path: '/virtual-root',
+    sourceReference: root,
+  })
+  t.equal(virtualRoot.edgesOut.get('a').type, 'dev')
+})