Reorder

* Avoid issues when using --conservative as seen in
  https://github.com/ruby/setup-ruby/pull/48, clarifies what's getting
  installed and simplifies the following logic.
* We'll probably need changes when Bundler 3 comes out anyway.

README.md

@@ -163,5 +163,5 @@ Please [update](https://github.com/ruby/setup-ruby/releases/tag/v1.13.0) if you
 ## Credits
 
 The current maintainer of this action is @eregon.
-Most of the Windows logic is from https://github.com/MSP-Greg/actions-ruby by MSP-Greg.
+Most of the Windows logic is based on work by MSP-Greg.
 Many thanks to MSP-Greg and Lars Kanis for the help with Ruby Installer.

dist/index.js

@@ -1058,7 +1058,7 @@ function setupPath(ruby, newPathEntries) {
     let cleanPath = originalPath.filter(entry => !/\bruby\b/i.test(entry))
 
     if (cleanPath.length !== originalPath.length) {
-        console.log("Entries removed from PATH to avoid conflicts with Ruby:")
+        console.log('Entries removed from PATH to avoid conflicts with Ruby:')
         for (const entry of originalPath) {
             if (!cleanPath.includes(entry)) {
                 console.log(`  ${entry}`)
@@ -1100,27 +1100,35 @@ async function installBundler(platform, rubyPrefix, engine, rubyVersion) {
     }
   }
 
-  let versionArray
+  if (bundlerVersion === 'latest') {
+    bundlerVersion = '2'
+  }
+
   if (rubyVersion.startsWith('2.2')) {
     console.log('Bundler 2 requires Ruby 2.3+, using Bundler 1 on Ruby 2.2')
-    versionArray = ['-v', '~> 1']
+    bundlerVersion = '1'
   } else if (/^\d+/.test(bundlerVersion)) {
-    versionArray = ['-v', `~> ${bundlerVersion}`]
-  } else if (bundlerVersion === 'latest') {
-    versionArray = []
+    // OK
   } else {
     throw new Error(`Cannot parse bundler input: ${bundlerVersion}`)
   }
 
-  if (engine === 'rubinius') {
-    console.log(`Rubinius only supports the version of Bundler shipped with it`)
-  } else if (bundlerVersion === '1' && engine === 'truffleruby') {
+  if (engine === 'ruby' && isHeadVersion(rubyVersion) && bundlerVersion === '2') {
+    console.log(`Using the Bundler version shipped with ${engine}-${rubyVersion}`)
+  } else if (engine === 'truffleruby' && bundlerVersion === '1') {
     console.log(`Using the Bundler version shipped with ${engine}`)
+  } else if (engine === 'rubinius') {
+    console.log(`Rubinius only supports the version of Bundler shipped with it`)
   } else {
-    await exec.exec(path.join(rubyPrefix, 'bin', 'gem'), ['install', 'bundler', ...versionArray, '--no-document'])
+    const gem = path.join(rubyPrefix, 'bin', 'gem')
+    await exec.exec(gem, ['install', 'bundler', '-v', `~> ${bundlerVersion}`, '--no-document'])
   }
 }
 
+function isHeadVersion(rubyVersion) {
+  return rubyVersion === 'head' || rubyVersion === 'mingw' || rubyVersion === 'mswin'
+}
+
 function getVirtualEnvironmentName() {
   const platform = os.platform()
   if (platform === 'linux') {

index.js

@@ -100,7 +100,7 @@ function setupPath(ruby, newPathEntries) {
     let cleanPath = originalPath.filter(entry => !/\bruby\b/i.test(entry))
 
     if (cleanPath.length !== originalPath.length) {
-        console.log("Entries removed from PATH to avoid conflicts with Ruby:")
+        console.log('Entries removed from PATH to avoid conflicts with Ruby:')
         for (const entry of originalPath) {
             if (!cleanPath.includes(entry)) {
                 console.log(`  ${entry}`)
@@ -142,27 +142,35 @@ async function installBundler(platform, rubyPrefix, engine, rubyVersion) {
     }
   }
 
-  let versionArray
+  if (bundlerVersion === 'latest') {
+    bundlerVersion = '2'
+  }
+
   if (rubyVersion.startsWith('2.2')) {
     console.log('Bundler 2 requires Ruby 2.3+, using Bundler 1 on Ruby 2.2')
-    versionArray = ['-v', '~> 1']
+    bundlerVersion = '1'
   } else if (/^\d+/.test(bundlerVersion)) {
-    versionArray = ['-v', `~> ${bundlerVersion}`]
-  } else if (bundlerVersion === 'latest') {
-    versionArray = []
+    // OK
   } else {
     throw new Error(`Cannot parse bundler input: ${bundlerVersion}`)
   }
 
-  if (engine === 'rubinius') {
-    console.log(`Rubinius only supports the version of Bundler shipped with it`)
-  } else if (bundlerVersion === '1' && engine === 'truffleruby') {
+  if (engine === 'ruby' && isHeadVersion(rubyVersion) && bundlerVersion === '2') {
+    console.log(`Using the Bundler version shipped with ${engine}-${rubyVersion}`)
+  } else if (engine === 'truffleruby' && bundlerVersion === '1') {
     console.log(`Using the Bundler version shipped with ${engine}`)
+  } else if (engine === 'rubinius') {
+    console.log(`Rubinius only supports the version of Bundler shipped with it`)
   } else {
-    await exec.exec(path.join(rubyPrefix, 'bin', 'gem'), ['install', 'bundler', ...versionArray, '--no-document'])
+    const gem = path.join(rubyPrefix, 'bin', 'gem')
+    await exec.exec(gem, ['install', 'bundler', '-v', `~> ${bundlerVersion}`, '--no-document'])
   }
 }
 
+function isHeadVersion(rubyVersion) {
+  return rubyVersion === 'head' || rubyVersion === 'mingw' || rubyVersion === 'mswin'
+}
+
 function getVirtualEnvironmentName() {
   const platform = os.platform()
   if (platform === 'linux') {