Merge d5bd7e8c9a into 0eb0e97082

* Add readme example for omitting `version`

* docs: more detailed explanations

---------

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

README.md

@@ -60,7 +60,9 @@ 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:
@@ -77,6 +79,23 @@ jobs:
           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

src/install-pnpm/run.ts

@@ -5,6 +5,7 @@ import { readFileSync } from 'fs'
 import path from 'path'
 import { execPath } from 'process'
 import util from 'util'
+import * as yaml from 'yaml'
 import { Inputs } from '../inputs'
 
 export async function runSelfInstaller(inputs: Inputs): Promise<number> {
@@ -78,10 +79,18 @@ Otherwise, please specify the pnpm version in the action configuration.`)
   }
 
   if (typeof packageManager !== 'string') {
-    throw new Error(`No pnpm version is specified.
+    if (GITHUB_WORKSPACE) {
+      try {
+        const { lockfileVersion } = yaml.parse(readFileSync(path.join(GITHUB_WORKSPACE, 'pnpm-lock.yaml'), 'utf8'))
+        const version = getPnpmVersionFromLockfile(lockfileVersion);
+        return `${ standalone ? '@pnpm/exe' : 'pnpm' }@${version}`
+      } catch (error: unknown) {
+        throw new Error(`No pnpm version is specified.
 Please specify it by one of the following ways:
   - in the GitHub Action config with the key "version"
   - in the package.json with the key "packageManager"`)
+      }
+    }
   }
 
   if (!packageManager.startsWith('pnpm@')) {
@@ -95,4 +104,21 @@ Please specify it by one of the following ways:
   return packageManager
 }
 
+function getPnpmVersionFromLockfile(
+  lockfileVersion: string | undefined
+): string | undefined {
+  switch (true) {
+    case lockfileVersion === '5.3':
+      return 'latest-6';
+    case lockfileVersion === '5.4':
+      return 'latest-7';
+    case lockfileVersion === '6.0' || lockfileVersion === '6.1':
+      return 'latest-8';
+    case lockfileVersion === '7.0' || lockfileVersion === '9.0':
+      return 'latest-9';
+    default:
+      return undefined;
+  }
+}
+
 export default runSelfInstaller