fix: auto installing peer dep in a workspace

.changeset/twenty-dragons-explode.md

@@ -0,0 +1,7 @@
+---
+"@pnpm/core": patch
+"@pnpm/resolve-dependencies": patch
+"pnpm": patch
+---
+
+Auto installing a peer dependency in a workspace that also has it as a dev dependency in another project [#5144](https://github.com/pnpm/pnpm/issues/5144).

packages/core/test/install/autoInstallPeers.ts

@@ -1,3 +1,5 @@
+import path from 'path'
+import assertProject from '@pnpm/assert-project'
 import { addDependenciesToPackage, install, mutateModules } from '@pnpm/core'
 import { prepareEmpty, preparePackages } from '@pnpm/prepare'
 import { addDistTag, REGISTRY_MOCK_PORT } from '@pnpm/registry-mock'
@@ -226,3 +228,41 @@ test('automatically install root peer dependencies', async () => {
     })
   }
 })
+
+test('automatically install peer dependency when it is a dev dependency in another workspace project', async () => {
+  prepareEmpty()
+
+  await mutateModules([
+    {
+      buildIndex: 0,
+      manifest: {
+        name: 'project-1',
+        devDependencies: {
+          'is-positive': '1.0.0',
+        },
+      },
+      mutation: 'install',
+      rootDir: path.resolve('project-1'),
+    },
+    {
+      buildIndex: 0,
+      manifest: {
+        name: 'project-2',
+        peerDependencies: {
+          'is-positive': '1.0.0',
+        },
+      },
+      mutation: 'install',
+      rootDir: path.resolve('project-2'),
+    },
+  ], await testDefaults({ autoInstallPeers: true }))
+
+  const project = assertProject(process.cwd())
+  const lockfile = await project.readLockfile()
+  expect(lockfile.importers['project-1'].devDependencies).toStrictEqual({
+    'is-positive': '1.0.0',
+  })
+  expect(lockfile.importers['project-2'].dependencies).toStrictEqual({
+    'is-positive': '1.0.0',
+  })
+})

packages/resolve-dependencies/src/index.ts

@@ -135,6 +135,16 @@ export default async function (
     }
 
     if (updatedManifest != null) {
+      if (opts.autoInstallPeers) {
+        if (updatedManifest.peerDependencies) {
+          const allDeps = getAllDependenciesFromManifest(updatedManifest)
+          for (const [peerName, peerRange] of Object.entries(updatedManifest.peerDependencies)) {
+            if (allDeps[peerName]) continue
+            updatedManifest.dependencies ??= {}
+            updatedManifest.dependencies[peerName] = peerRange
+          }
+        }
+      }
       const projectSnapshot = opts.wantedLockfile.importers[project.id]
       opts.wantedLockfile.importers[project.id] = addDirectDependenciesToLockfile(
         updatedManifest,
@@ -334,14 +344,7 @@ function addDirectDependenciesToLockfile (
     return acc
   }, {})
 
-  let allDepsObj = getAllDependenciesFromManifest(newManifest)
-  if (autoInstallPeers) {
-    allDepsObj = {
-      ...newManifest.peerDependencies,
-      ...allDepsObj,
-    }
-  }
-  const allDeps = Array.from(new Set(Object.keys(allDepsObj)))
+  const allDeps = Array.from(new Set(Object.keys(getAllDependenciesFromManifest(newManifest))))
 
   for (const alias of allDeps) {
     if (directDependenciesByAlias[alias]) {