Do not install Bundler if RubyGems was updated

* Updating RubyGems will install Bundler as a side effect.
* Fixes #326

Author: eregon

action.yml

@@ -15,7 +15,8 @@ inputs:
       For 'default', no action is taken and the version of RubyGems that comes with Ruby by default is used.
       For 'latest', `gem update --system` is run to update to the latest RubyGems version.
       Similarly, if a version number is given, `gem update --system <version>` is run to update to that version of RubyGems, as long as that version is newer than the one provided by default.
-      Defaults to 'default'.
+    required: false
+    default: 'default'
   bundler:
     description: |
       The version of Bundler to install. Either 'none', 'latest', 'Gemfile.lock', or a version number (e.g., 1, 2, 2.1, 2.1.4).

bundler.js

@@ -50,9 +50,14 @@ async function afterLockFile(lockFile, platform, engine, rubyVersion) {
   }
 }
 
-export async function installBundler(bundlerVersionInput, lockFile, platform, rubyPrefix, engine, rubyVersion) {
+export async function installBundler(bundlerVersionInput, rubygemsInputSet, lockFile, platform, rubyPrefix, engine, rubyVersion) {
   let bundlerVersion = bundlerVersionInput
 
+  if (rubygemsInputSet && bundlerVersion === 'default') {
+    console.log('Using the Bundler installed by updating RubyGems')
+    return 'unknown'
+  }
+
   if (bundlerVersion === 'default' || bundlerVersion === 'Gemfile.lock') {
     bundlerVersion = readBundledWithFromGemfileLock(lockFile)
 

dist/index.js

@@ -66,7 +66,8 @@ export async function setupRuby(options = {}) {
   await common.measure('Print Ruby version', async () =>
     await exec.exec('ruby', ['--version']))
 
-  if (inputs['rubygems'] !== 'default') {
+  const rubygemsInputSet = inputs['rubygems'] !== 'default'
+  if (rubygemsInputSet) {
     await common.measure('Updating RubyGems', async () =>
       rubygems.rubygemsUpdate(inputs['rubygems'], rubyPrefix))
   }
@@ -79,11 +80,11 @@ export async function setupRuby(options = {}) {
   }
 
   const [gemfile, lockFile] = bundler.detectGemfiles()
-  let bundlerVersion = "unknown"
+  let bundlerVersion = 'unknown'
 
   if (inputs['bundler'] !== 'none') {
     bundlerVersion = await common.measure('Installing Bundler', async () =>
-      bundler.installBundler(inputs['bundler'], lockFile, platform, rubyPrefix, engine, version))
+      bundler.installBundler(inputs['bundler'], rubygemsInputSet, lockFile, platform, rubyPrefix, engine, version))
   }
 
   if (inputs['bundler-cache'] === 'true') {