Workaround the CRuby bug of bin/bundle in bash on Windows

* Fixes ruby#371
* See https://bugs.ruby-lang.org/issues/18970

.github/workflows/test.yml

@@ -96,19 +96,33 @@ jobs:
     - run: bundle exec rake --version
     - run: bundle exec rake
 
+    # Ensure the same bundle commands work in bash on Windows
+    - name: bundle install (bash)
+      run: bundle install
+      shell: bash
+      if: startsWith(matrix.os, 'windows')
+    - name: bundle exec rake --version (bash)
+      run: bundle exec rake --version
+      shell: bash
+      if: startsWith(matrix.os, 'windows')
+    - name: bundle exec rake (bash)
+      run: bundle exec rake
+      shell: bash
+      if: startsWith(matrix.os, 'windows')
+
     - name: Test `gem github:` in a Gemfile
       run: bundle install
       env:
         BUNDLE_GEMFILE: ${{ github.workspace }}/gemfiles/gem_from_github.gemfile
 
-    - name: which ruby, rake
+    - name: which ruby, rake bundle
       if: "!startsWith(matrix.os, 'windows')"
-      run: which -a ruby rake
-    - name: where ruby, rake
+      run: which -a ruby rake bundle
+    - name: where ruby, rake, bundle
       if: startsWith(matrix.os, 'windows')
       run: |
         $ErrorActionPreference = 'Continue'
-        $where = 'ruby', 'rake'
+        $where = 'ruby', 'rake', 'bundle'
         foreach ($e in $where) {
           $rslt = where.exe $e 2>&1 | Out-String
           if ($rslt.contains($e)) { echo $rslt.Trim() }
@@ -117,7 +131,7 @@ jobs:
         }
     - name: bash test
       shell: bash
-      run: echo ~
+      run: echo ~ && which -a bundle
     - name: Windows JRuby
       if: startsWith(matrix.os, 'windows') && startsWith(matrix.ruby, 'jruby')
       run: gem install sassc

bundler.js

@@ -72,8 +72,14 @@ export async function installBundler(bundlerVersionInput, rubygemsInputSet, lock
 
   if (bundlerVersion === 'default') {
     if (common.isBundler2dot2Default(engine, rubyVersion)) {
-      console.log(`Using Bundler 2 shipped with ${engine}-${rubyVersion}`)
-      return '2'
+      if (common.windows && engine === 'ruby') {
+        // https://github.com/ruby/setup-ruby/issues/371
+        console.log(`Installing latest Bundler for ${engine}-${rubyVersion} on Windows because bin/bundle does not work in bash otherwise`)
+        bundlerVersion = 'latest'
+      } else {
+        console.log(`Using Bundler 2 shipped with ${engine}-${rubyVersion}`)
+        return '2'
+      }
     } else if (common.hasBundlerDefaultGem(engine, rubyVersion)) {
       // Those Rubies have a old Bundler default gem < 2.2 which does not work well for `gem 'foo', github: 'foo/foo'`:
       // https://github.com/ruby/setup-ruby/issues/358#issuecomment-1195899304