Add Debian 12 and 13 support

README.md

@@ -50,9 +50,12 @@ The action works on these [GitHub-hosted runners](https://docs.github.com/en/act
 | Operating System | Supported |
 | ---------------- | --------- |
 | Ubuntu  | `ubuntu-22.04`, `ubuntu-24.04`, `ubuntu-26.04`, `ubuntu-22.04-arm`, `ubuntu-24.04-arm`, `ubuntu-26.04-arm` |
+| Debian  | `debian-12` (Ubuntu 22.04 builds), `debian-13` (Ubuntu 24.04 builds), x64 and arm64 |
 | macOS   | `macos-14` and newer versions |
 | Windows | `windows-2022`, `windows-2025`, `windows-11-arm` |
 
+Debian is included so this action can run on Forgejo `act_runner` job containers. There are no Debian-specific ruby-builder artifacts; the action downloads the Ubuntu builds listed above. That works because Debian 12/13 have a newer glibc than those Ubuntu images and still ship `libssl.so.3`. `/opt/hostedtoolcache` must be writable. Missing CRuby runtime packages (`libssl3`, `libyaml-0-2`, `libgmp10`, …) are installed with `apt-get` when the job is root.
+
 Not all combinations of runner images and versions are supported.
 The list of available Ruby versions can be seen in [ruby-builder-versions.json](ruby-builder-versions.json) for Ubuntu and macOS
 (although some combinations are not available, see [the full list](https://github.com/ruby/ruby-builder/releases/tag/toolcache))
@@ -273,7 +276,8 @@ This follows the [recommendations](https://github.com/actions/toolkit/blob/maste
 
 ## Using self-hosted runners
 
-This action might work with [self-hosted runners](https://docs.github.com/en/actions/hosting-your-own-runners/about-self-hosted-runners)
+Debian 12 and 13 runners (including Forgejo) are supported directly; see [Supported Platforms](#supported-platforms).
+For other self-hosted Linux, this action might work with [self-hosted runners](https://docs.github.com/en/actions/hosting-your-own-runners/about-self-hosted-runners)
 if the [Runner Image](https://github.com/actions/runner-images) is very similar to the ones used by GitHub runners. Notably:
 
 * Make sure to use the same operating system and version.

common.js

@@ -193,12 +193,41 @@ const GitHubHostedPlatforms = [
   'windows-11-arm64'
 ]
 
+// ruby-builder artifacts are Ubuntu-specific. Debian can run them when its glibc
+// is newer than the builder image and libssl is still SONAME 3.
+// Debian 12 (glibc 2.36) → Ubuntu 22.04 (glibc 2.35).
+// Debian 13 (glibc 2.41) → Ubuntu 24.04 (glibc 2.39).
+const DebianToUbuntuBuilder = {
+  '12': 'ubuntu-22.04',
+  '13': 'ubuntu-24.04',
+}
+
+function debianMajorVersion() {
+  return getOSVersion().split('.')[0]
+}
+
+// Platform string used in ruby-builder download URLs (ubuntu-XX.YY, not debian-N).
+export function getRubyBuilderPlatform() {
+  const name = getOSName()
+  if (name === 'debian') {
+    const mapped = DebianToUbuntuBuilder[debianMajorVersion()]
+    if (mapped) {
+      return mapped
+    }
+  }
+  return getOSNameVersion()
+}
+
 // Precisely: whether we have builds for that platform and there are GitHub-hosted runners to test it
 function isSupportedPlatform() {
   const platform = getOSName()
   switch (platform) {
     case 'ubuntu':
       return GitHubHostedPlatforms.includes(getOSNameVersionArch())
+    case 'debian': {
+      const mapped = DebianToUbuntuBuilder[debianMajorVersion()]
+      return mapped !== undefined && GitHubHostedPlatforms.includes(`${mapped}-${os.arch()}`)
+    }
     case 'macos':
       // See https://github.com/ruby/ruby-builder/blob/master/README.md#naming
       // 13 on arm64 because of old macos-arm-oss runners
@@ -318,6 +347,7 @@ function getDefaultToolCachePath() {
   const platform = getOSName()
   switch (platform) {
     case 'ubuntu':
+    case 'debian':
       return '/opt/hostedtoolcache'
     case 'macos':
       return '/Users/runner/hostedtoolcache'

ruby-builder.js

@@ -16,6 +16,15 @@ export function getAvailableVersions(platform, engine) {
 }
 
 export async function install(platform, engine, version) {
+  const builderPlatform = common.getRubyBuilderPlatform()
+  if (builderPlatform !== platform) {
+    console.log(`Detected ${common.getOSNameVersionArch()}; using ${builderPlatform} prebuilt Ruby binaries`)
+  }
+
+  if (platform.startsWith('debian-')) {
+    await ensureDebianRuntimeLibs()
+  }
+
   let rubyPrefix, inToolCache
   if (common.shouldUseToolCache(engine, version)) {
     inToolCache = common.toolCacheFind(engine, version)
@@ -106,8 +115,8 @@ function getDownloadURL(platform, engine, version) {
     builderPlatform = `windows-${os.arch()}`
   } else if (platform.startsWith('macos-')) {
     builderPlatform = `darwin-${os.arch()}`
-  } else if (platform.startsWith('ubuntu-')) {
-    builderPlatform = `${platform}-${os.arch()}`
+  } else if (platform.startsWith('ubuntu-') || platform.startsWith('debian-')) {
+    builderPlatform = `${common.getRubyBuilderPlatform()}-${os.arch()}`
   }
 
   if (builderPlatform === null || !['x64', 'arm64'].includes(os.arch())) {
@@ -121,6 +130,26 @@ function getDownloadURL(platform, engine, version) {
   }
 }
 
+const debianRuntimePackages = ['libssl3', 'libyaml-0-2', 'libgmp10', 'zlib1g', 'libcrypt1', 'libffi8']
+
+async function ensureDebianRuntimeLibs() {
+  const missing = []
+  for (const pkg of debianRuntimePackages) {
+    const status = await exec.exec('dpkg', ['-s', pkg], { ignoreReturnCode: true, silent: true })
+    if (status !== 0) {
+      missing.push(pkg)
+    }
+  }
+  if (missing.length === 0) {
+    return
+  }
+
+  await common.measure(`Installing Ruby runtime libraries (${missing.join(', ')})`, async () => {
+    await exec.exec('apt-get', ['update', '-qq'])
+    await exec.exec('apt-get', ['install', '-y', '-qq', ...missing])
+  })
+}
+
 function getLatestHeadBuildURL(platform, engine, version) {
   var repo = `${engine}-dev-builder`
   if (engine === 'truffleruby+graalvm') {