Document the logic for whether to install Bundler

https://github.com/actions/virtual-environments/blob/dee50eebffa60a7dd9149033675d44a027dd6b33/README.md#available-environments

README.md

@@ -15,7 +15,7 @@ This action currently supports these versions of MRI, JRuby and TruffleRuby:
 | Interpreter | Versions |
 | ----------- | -------- |
 | `ruby` | 2.1.9, 2.2, 2.3.0 - 2.3.8, 2.4.0 - 2.4.10, 2.5.0 - 2.5.8, 2.6.0 - 2.6.6, 2.7.2, 3.0.0, head, debug, mingw, mswin |
-| `jruby` | 9.1.17.0, 9.2.9.0 - 9.2.13.0, head |
+| `jruby` | 9.1.17.0, 9.2.9.0 - 9.2.16.0, head |
 | `truffleruby` | 19.3.0 - 21.0.0, head |
 
 `ruby-debug` is the same as `ruby-head` but with assertions enabled (`-DRUBY_DEBUG=1`).  
@@ -38,7 +38,7 @@ The action works for all [GitHub-hosted runners](https://help.github.com/en/acti
 
 | Operating System | Recommended | Other Supported Versions |
 | ----------- | -------- | -------- |
-| Ubuntu  | `ubuntu-latest`  (= `ubuntu-18.04`) | `ubuntu-20.04`, `ubuntu-16.04` |
+| Ubuntu  | `ubuntu-latest`  (= `ubuntu-20.04`) | `ubuntu-18.04`, `ubuntu-16.04` |
 | macOS   | `macos-latest`   (= `macos-10.15`)  | `macos-11.0` |
 | Windows | `windows-latest` (= `windows-2019`) | `windows-2016` |
 
@@ -83,6 +83,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest]
+        # Due to https://github.com/actions/runner/issues/849, we have to use quotes for '3.0'
         ruby: [2.5, 2.6, 2.7, '3.0', head, jruby, jruby-head, truffleruby, truffleruby-head]
     runs-on: ${{ matrix.os }}
     steps:
@@ -110,7 +111,7 @@ jobs:
       BUNDLE_GEMFILE: gemfiles/${{ matrix.gemfile }}.gemfile
     steps:
       - uses: actions/checkout@v2
-      - uses: ./
+      - uses: ruby/setup-ruby@v1
         with:
           ruby-version: 2.6
           bundler-cache: true # runs 'bundle install' and caches installed gems automatically
@@ -166,8 +167,9 @@ as shown in the [example](#matrix-of-gemfiles).
 
 When using `bundler-cache: true` you might notice there is no good place to run `bundle config ...` commands.
 These can be replaced by `BUNDLE_*` environment variables, which are also faster.
-They should be set the `env` at the job level as shown in the [example](#matrix-of-gemfiles).
+They should be set in the `env` at the job level as shown in the [example](#matrix-of-gemfiles).
-See the [Bundler docs](https://bundler.io/man/bundle-config.1.html) or look at `.bundle/config` locally for the environment variable names,
+To find the correct the environment variable name, see the [Bundler docs](https://bundler.io/man/bundle-config.1.html) or look at `.bundle/config` after running `bundle config --local KEY VALUE` locally.
+You might need to `"`-quote the environment variable name in YAML if it has unusual characters like `/`.
 
 To perform caching, this action will use `bundle config --local path $PWD/vendor/bundle`.  
 Therefore, the Bundler `path` should not be changed in your workflow for the cache to work (no `bundle config path`).

bundler.js

@@ -72,8 +72,8 @@ export async function installBundler(bundlerVersionInput, lockFile, platform, ru
   if (engine === 'ruby' && rubyVersion.match(/^2\.[012]/)) {
     console.log('Bundler 2 requires Ruby 2.3+, using Bundler 1 on Ruby <= 2.2')
     bundlerVersion = '1'
-  } else if (engine === 'ruby' && rubyVersion.startsWith('2.3')) {
+  } else if (engine === 'ruby' && rubyVersion.match(/^2\.3\.[01]/)) {
-    console.log('Ruby 2.3 has a bug with Bundler 2 (https://github.com/rubygems/rubygems/issues/3570), using Bundler 1 instead on Ruby 2.3')
+    console.log('Ruby 2.3.0 and 2.3.1 have shipped with an old rubygems that only works with Bundler 1')
     bundlerVersion = '1'
   } else if (engine === 'jruby' && rubyVersion.startsWith('9.1')) { // JRuby 9.1 targets Ruby 2.3, treat it the same
     console.log('JRuby 9.1 has a bug with Bundler 2 (https://github.com/ruby/setup-ruby/issues/108), using Bundler 1 instead on JRuby 9.1')
@@ -81,6 +81,8 @@ export async function installBundler(bundlerVersionInput, lockFile, platform, ru
   }
 
   if (common.isHeadVersion(rubyVersion) && common.isBundler2Default(engine, rubyVersion) && bundlerVersion.startsWith('2')) {
+    // Avoid installing a newer Bundler version for head versions as it might not work.
+    // For releases, even if they ship with Bundler 2 we install the latest Bundler.
     console.log(`Using Bundler 2 shipped with ${engine}-${rubyVersion}`)
   } else if (engine === 'truffleruby' && !common.isHeadVersion(rubyVersion) && bundlerVersion.startsWith('1')) {
     console.log(`Using Bundler 1 shipped with ${engine}`)

common.js

@@ -59,7 +59,9 @@ export function isBundler2Default(engine, rubyVersion) {
   if (engine === 'ruby') {
     return isHeadVersion(rubyVersion) || floatVersion(rubyVersion) >= 2.7
   } else if (engine === 'truffleruby') {
-    return isHeadVersion(rubyVersion)
+    return isHeadVersion(rubyVersion) || floatVersion(rubyVersion) >= 21.0
+  } else if (engine === 'jruby') {
+    return isHeadVersion(rubyVersion) || floatVersion(rubyVersion) >= 9.3
   } else {
     return false
   }

dist/index.js

@@ -32851,7 +32851,9 @@ function isBundler2Default(engine, rubyVersion) {
   if (engine === 'ruby') {
     return isHeadVersion(rubyVersion) || floatVersion(rubyVersion) >= 2.7
   } else if (engine === 'truffleruby') {
-    return isHeadVersion(rubyVersion)
+    return isHeadVersion(rubyVersion) || floatVersion(rubyVersion) >= 21.0
+  } else if (engine === 'jruby') {
+    return isHeadVersion(rubyVersion) || floatVersion(rubyVersion) >= 9.3
   } else {
     return false
   }
@@ -44608,8 +44610,8 @@ async function installBundler(bundlerVersionInput, lockFile, platform, rubyPrefi
   if (engine === 'ruby' && rubyVersion.match(/^2\.[012]/)) {
     console.log('Bundler 2 requires Ruby 2.3+, using Bundler 1 on Ruby <= 2.2')
     bundlerVersion = '1'
-  } else if (engine === 'ruby' && rubyVersion.startsWith('2.3')) {
+  } else if (engine === 'ruby' && rubyVersion.match(/^2\.3\.[01]/)) {
-    console.log('Ruby 2.3 has a bug with Bundler 2 (https://github.com/rubygems/rubygems/issues/3570), using Bundler 1 instead on Ruby 2.3')
+    console.log('Ruby 2.3.0 and 2.3.1 have shipped with an old rubygems that only works with Bundler 1')
     bundlerVersion = '1'
   } else if (engine === 'jruby' && rubyVersion.startsWith('9.1')) { // JRuby 9.1 targets Ruby 2.3, treat it the same
     console.log('JRuby 9.1 has a bug with Bundler 2 (https://github.com/ruby/setup-ruby/issues/108), using Bundler 1 instead on JRuby 9.1')
@@ -44617,6 +44619,8 @@ async function installBundler(bundlerVersionInput, lockFile, platform, rubyPrefi
   }
 
   if (common.isHeadVersion(rubyVersion) && common.isBundler2Default(engine, rubyVersion) && bundlerVersion.startsWith('2')) {
+    // Avoid installing a newer Bundler version for head versions as it might not work.
+    // For releases, even if they ship with Bundler 2 we install the latest Bundler.
     console.log(`Using Bundler 2 shipped with ${engine}-${rubyVersion}`)
   } else if (engine === 'truffleruby' && !common.isHeadVersion(rubyVersion) && bundlerVersion.startsWith('1')) {
     console.log(`Using Bundler 1 shipped with ${engine}`)
@@ -45354,7 +45358,7 @@ function getVersions(platform) {
     ],
     "jruby": [
       "9.1.17.0",
-      "9.2.9.0", "9.2.10.0", "9.2.11.0", "9.2.11.1", "9.2.12.0", "9.2.13.0", "9.2.14.0",
+      "9.2.9.0", "9.2.10.0", "9.2.11.0", "9.2.11.1", "9.2.12.0", "9.2.13.0", "9.2.14.0", "9.2.15.0", "9.2.16.0",
       "head"
     ],
     "truffleruby": [

ruby-builder-versions.js

@@ -13,7 +13,7 @@ export function getVersions(platform) {
     ],
     "jruby": [
       "9.1.17.0",
-      "9.2.9.0", "9.2.10.0", "9.2.11.0", "9.2.11.1", "9.2.12.0", "9.2.13.0", "9.2.14.0",
+      "9.2.9.0", "9.2.10.0", "9.2.11.0", "9.2.11.1", "9.2.12.0", "9.2.13.0", "9.2.14.0", "9.2.15.0", "9.2.16.0",
       "head"
     ],
     "truffleruby": [