docs: remove redundant manual cache due to setup-node cache (#131)

* Add readme example for omitting `version`

* docs: more detailed explanations

---------

Co-authored-by: Khải <hvksmr1996@gmail.com>

README.md

@@ -1,3 +1,7 @@
+> ## :warning: Upgrade from v2!
+>
+> The v2 version of this action [has stopped working](https://github.com/pnpm/action-setup/issues/135) with newer Node.js versions. Please, upgrade to the latest version to fix any issues.
+
 # Setup pnpm
 
 Install pnpm package manager.
@@ -60,7 +64,9 @@ Location of `pnpm` and `pnpx` command.
 
 ## Usage example
 
-### Just install pnpm
+### Install only pnpm without `packageManager`
+
+This works when the repo either doesn't have a `package.json` or has a `package.json` but it doesn't specify `packageManager`.
 
 ```yaml
 on:
@@ -72,11 +78,28 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: pnpm/action-setup@v3
+      - uses: pnpm/action-setup@v4
         with:
           version: 8
 ```
 
+###  Install only pnpm with `packageManager`
+
+Omit `version` input to use the version in the [`packageManager` field in the `package.json`](https://nodejs.org/api/corepack.html).
+
+```yaml
+on:
+  - push
+  - pull_request
+
+jobs:
+  install:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: pnpm/action-setup@v4
+```
+
 ### Install pnpm and a few npm packages
 
 ```yaml
@@ -91,7 +114,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: pnpm/action-setup@v3
+      - uses: pnpm/action-setup@v4
         with:
           version: 8
           run_install: |
@@ -115,29 +138,17 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Install Node.js
-        uses: actions/setup-node@v4
-        with:
-          node-version: 20
-
-      - uses: pnpm/action-setup@v3
+      - uses: pnpm/action-setup@v4
         name: Install pnpm
         with:
           version: 8
           run_install: false
 
-      - name: Get pnpm store directory
-        shell: bash
-        run: |
-          echo "STORE_PATH=$(pnpm store path --silent)" >> $GITHUB_ENV
-
-      - uses: actions/cache@v4
-        name: Setup pnpm cache
+      - name: Install Node.js
+        uses: actions/setup-node@v4
         with:
-          path: ${{ env.STORE_PATH }}
-          key: ${{ runner.os }}-pnpm-store-${{ hashFiles('**/pnpm-lock.yaml') }}
-          restore-keys: |
-            ${{ runner.os }}-pnpm-store-
+          node-version: 20
+          cache: 'pnpm'
 
       - name: Install dependencies
         run: pnpm install

action.yml

@@ -23,6 +23,11 @@ inputs:
     description: When set to true, @pnpm/exe, which is a Node.js bundled package, will be installed, enabling using pnpm without Node.js.
     required: false
     default: 'false'
+outputs:
+  dest:
+    description: Expanded path of inputs#dest
+  bin_dest:
+    description: Location of `pnpm` and `pnpx` command
 runs:
   using: node20
   main: dist/index.js

src/install-pnpm/run.ts

@@ -1,8 +1,10 @@
 import { addPath, exportVariable } from '@actions/core'
 import { spawn } from 'child_process'
-import { rm, writeFile, readFile, mkdir } from 'fs/promises'
+import { rm, writeFile, mkdir } from 'fs/promises'
+import { readFileSync } from 'fs'
 import path from 'path'
 import { execPath } from 'process'
+import util from 'util'
 import { Inputs } from '../inputs'
 
 export async function runSelfInstaller(inputs: Inputs): Promise<number> {
@@ -41,18 +43,40 @@ async function readTarget(opts: {
   readonly standalone: boolean
 }) {
   const { version, packageJsonFile, standalone } = opts
-
-  if (version) return `${ standalone ? '@pnpm/exe' : 'pnpm' }@${version}`
-
   const { GITHUB_WORKSPACE } = process.env
+
+  let packageManager
+
+  if (GITHUB_WORKSPACE) {
+    try {
+      ({ packageManager } = JSON.parse(readFileSync(path.join(GITHUB_WORKSPACE, packageJsonFile), 'utf8')))
+    } catch (error: unknown) {
+      // Swallow error if package.json doesn't exist in root
+      if (!util.types.isNativeError(error) || !('code' in error) || error.code !== 'ENOENT') throw error
+    }
+  }
+
+  if (version) {
+    if (
+      typeof packageManager === 'string' &&
+      packageManager.replace('pnpm@', '') !== version
+    ) {
+      throw new Error(`Multiple versions of pnpm specified:
+  - version ${version} in the GitHub Action config with the key "version"
+  - version ${packageManager} in the package.json with the key "packageManager"
+Remove one of these versions to avoid version mismatch errors like ERR_PNPM_BAD_PM_VERSION`)
+    }
+    
+    return `${ standalone ? '@pnpm/exe' : 'pnpm' }@${version}`
+  }
+
   if (!GITHUB_WORKSPACE) {
     throw new Error(`No workspace is found.
-If you're intended to let pnpm/action-setup read preferred pnpm version from the "packageManager" field in the package.json file,
+If you've intended to let pnpm/action-setup read preferred pnpm version from the "packageManager" field in the package.json file,
 please run the actions/checkout before pnpm/action-setup.
 Otherwise, please specify the pnpm version in the action configuration.`)
   }
 
-  const { packageManager } = JSON.parse(await readFile(path.join(GITHUB_WORKSPACE, packageJsonFile), 'utf8'))
   if (typeof packageManager !== 'string') {
     throw new Error(`No pnpm version is specified.
 Please specify it by one of the following ways:
@@ -64,7 +88,7 @@ Please specify it by one of the following ways:
     throw new Error('Invalid packageManager field in package.json')
   }
 
-  if(standalone){
+  if (standalone) {
     return packageManager.replace('pnpm@', '@pnpm/exe@')
   }