Add support for .tool-versions

* See https://stackoverflow.com/a/304447/388803

.github/workflows/test.yml

@@ -15,7 +15,7 @@ jobs:
       matrix:
         os: [ ubuntu-16.04, ubuntu-18.04, macos-latest, windows-latest ]
         # Use various version syntaxes here for testing
-        ruby: [ .ruby-version, 2.2, 2.3, 2.7.0, ruby-head, jruby, truffleruby, truffleruby-head, rubinius ]
+        ruby: [ .ruby-version, .tool-versions, 2.2, 2.3, ruby-head, jruby, truffleruby, truffleruby-head, rubinius ]
         exclude:
         - os: windows-latest
           ruby: truffleruby

.tool-versions

@@ -0,0 +1,2 @@
+nodejs 12.0.0
+ruby 2.7.0

README.md

@@ -91,7 +91,11 @@ jobs:
 * short version like `2.6`, automatically using the latest release matching that version (`2.6.5`)
 * version only like `2.6.5`, assumes MRI for the engine
 * engine only like `truffleruby`, uses the latest stable release of that implementation
-* `.ruby-version` (also the default value) reads from the project's `.ruby-version` file
+
+
+* `.ruby-version` reads from the project's `.ruby-version` file
+* `.tool-versions` reads from the project's `.tool-versions` file
+* If the `ruby-version` input is not specified, `.ruby-version` is tried first, followed by `.tool-versions`
 
 ### Bundler
 
@@ -117,7 +121,8 @@ You can cache the installed gems with these two steps:
 ```
 
 When using a single job with a Ruby version, replace `${{ matrix.ruby }}` with the Ruby version.  
-When using `.ruby-version`, replace `${{ matrix.ruby }}` with `${{ hashFiles('.ruby-version') }}`.
+When using `.ruby-version`, replace `${{ matrix.ruby }}` with `${{ hashFiles('.ruby-version') }}`.  
+When using `.tool-versions`, replace `${{ matrix.ruby }}` with `${{ hashFiles('.tool-versions') }}`.
 
 This uses the [cache action](https://github.com/actions/cache).
 The code above is a more complete version of the [Ruby - Bundler example](https://github.com/actions/cache/blob/master/examples.md#ruby---bundler).
@@ -130,7 +135,7 @@ It is recommended to first get your build working on Ubuntu and macOS before try
 
 * The default shell on Windows is not Bash but [PowerShell](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/workflow-syntax-for-github-actions#using-a-specific-shell).
   This can lead issues such as multi-line scripts [not working as expected](https://github.com/ruby/setup-ruby/issues/13).
-* The `PATH` contains [multiple compiler toolchains](https://github.com/ruby/setup-ruby/issues/19). Use `where` to debug which tool is used.
+* The `PATH` contains [multiple compiler toolchains](https://github.com/ruby/setup-ruby/issues/19). Use `where.exe` to debug which tool is used.
 * MSYS2 is prepended to the `PATH`, similar to what RubyInstaller2 does.
 * JRuby on Windows has a known bug that `bundle exec rake` [fails](https://github.com/ruby/setup-ruby/issues/18).
 

action.yml

@@ -8,7 +8,7 @@ inputs:
   ruby-version:
     description: 'Engine and version to use, see the syntax in the README. Reads from .ruby-version if unset.'
     required: false
-    default: '.ruby-version'
+    default: 'default'
 outputs:
   ruby-prefix:
     description: 'The prefix of the installed ruby'

dist/index.js

@@ -1416,9 +1416,24 @@ async function run() {
 }
 
 function parseRubyEngineAndVersion(rubyVersion) {
+  if (rubyVersion === 'default') {
+    if (fs.existsSync('.ruby-version')) {
+      rubyVersion = '.ruby-version'
+    } else if (fs.existsSync('.tool-versions')) {
+      rubyVersion = '.tool-versions'
+    } else {
+      throw new Error('input ruby-version needs to be specified if no .ruby-version or .tool-versions file exists')
+    }
+  }
+
   if (rubyVersion === '.ruby-version') { // Read from .ruby-version
     rubyVersion = fs.readFileSync('.ruby-version', 'utf8').trim()
     console.log(`Using ${rubyVersion} as input from file .ruby-version`)
+  } else if (rubyVersion === '.tool-versions') { // Read from .tool-versions
+    const toolVersions = fs.readFileSync('.tool-versions', 'utf8').trim()
+    const rubyLine = toolVersions.split(/\r?\n/).filter(e => e.match(/^ruby\s/))[0]
+    rubyVersion = rubyLine.split(/\s+/, 2)[1]
+    console.log(`Using ${rubyVersion} as input from file .tool-versions`)
   }
 
   let engine, version

index.js

@@ -25,9 +25,24 @@ async function run() {
 }
 
 function parseRubyEngineAndVersion(rubyVersion) {
+  if (rubyVersion === 'default') {
+    if (fs.existsSync('.ruby-version')) {
+      rubyVersion = '.ruby-version'
+    } else if (fs.existsSync('.tool-versions')) {
+      rubyVersion = '.tool-versions'
+    } else {
+      throw new Error('input ruby-version needs to be specified if no .ruby-version or .tool-versions file exists')
+    }
+  }
+
   if (rubyVersion === '.ruby-version') { // Read from .ruby-version
     rubyVersion = fs.readFileSync('.ruby-version', 'utf8').trim()
     console.log(`Using ${rubyVersion} as input from file .ruby-version`)
+  } else if (rubyVersion === '.tool-versions') { // Read from .tool-versions
+    const toolVersions = fs.readFileSync('.tool-versions', 'utf8').trim()
+    const rubyLine = toolVersions.split(/\r?\n/).filter(e => e.match(/^ruby\s/))[0]
+    rubyVersion = rubyLine.split(/\s+/, 2)[1]
+    console.log(`Using ${rubyVersion} as input from file .tool-versions`)
   }
 
   let engine, version