feat: throw error when multiple versions specified (#122)

* Throw error when multiple versions specified

* fix: fmt

* fix: fmt

* Swallow error on ENOENT

* Match versions

* refactor: install pnpm

---------

Co-authored-by: Khải <hvksmr1996@gmail.com>
Co-authored-by: Zoltan Kochan <z@kochan.io>

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> {
@@ -41,10 +43,33 @@ 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,
@@ -52,7 +77,6 @@ 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@')
   }