Use a hardcoded toolcache path since we need to extract there to let Ruby work

Author: eregon

README.md

@@ -203,10 +203,10 @@ if the [virtual environment](https://github.com/actions/virtual-environments) is
 * Make sure to use the same operating system and version.
 * Make sure to use the same version of libssl.
 * Make sure that the operating system has `libyaml-0` installed
-* The environment variable `RUNNER_TOOL_CACHE` must be set to same value as on GitHub-hosted runners
-  (`/opt/hostedtoolcache` on Linux, `/Users/runner/hostedtoolcache` on macOS, `C:\hostedtoolcache\windows` on Windows).
-* That directory must be writable by the `runner` user.
-* The runner software is running as user `runner` with a home directory of `/home/runner`, or you have created a symlink for the home directory of whatever user that the runner is running as to `/home/runner`.
+* The default tool cache directory (`/opt/hostedtoolcache` on Linux, `/Users/runner/hostedtoolcache` on macOS,
+  `C:/hostedtoolcache/windows` on Windows) must be writable by the `runner` user.
+  This is necessary since the Ruby builds embed the install path when built and cannot be moved around.
+* `/home/runner` must be writable by the `runner` user.
 
 In other cases, please use a system Ruby or [install Ruby manually](https://github.com/postmodern/chruby/wiki#installing-rubies) instead.
 

common.js

@@ -63,11 +63,21 @@ export function shouldExtractInToolCache(engine, version) {
   return engine === 'ruby' && !isHeadVersion(version)
 }
 
-export function getToolCacheRubyPrefix(version) {
-  const toolCache = process.env['RUNNER_TOOL_CACHE']
-  if (!toolCache) {
-    throw new Error('$RUNNER_TOOL_CACHE must be set')
+function getPlatformToolCache(platform) {
+  // Hardcode paths rather than using $RUNNER_TOOL_CACHE because the prebuilt Rubies cannot be moved anyway
+  if (platform.startsWith('ubuntu-')) {
+    return '/opt/hostedtoolcache'
+  } else if (platform.startsWith('macos-')) {
+    return '/Users/runner/hostedtoolcache'
+  } else if (platform.startsWith('windows-')) {
+    return 'C:/hostedtoolcache/windows'
+  } else {
+    throw new Error('Unknown platform')
   }
+}
+
+export function getToolCacheRubyPrefix(platform, version) {
+  const toolCache = getPlatformToolCache(platform)
   return path.join(toolCache, 'Ruby', version, 'x64')
 }
 

dist/index.js

@@ -23,7 +23,7 @@ export async function install(platform, engine, version) {
 async function downloadAndExtract(platform, engine, version) {
   let rubyPrefix
   if (common.shouldExtractInToolCache(engine, version)) {
-    rubyPrefix = common.getToolCacheRubyPrefix(version)
+    rubyPrefix = common.getToolCacheRubyPrefix(platform, version)
   } else if (windows) {
     rubyPrefix = path.join(`${common.drive}:`, `${engine}-${version}`)
   } else {

ruby-builder.js

@@ -38,7 +38,7 @@ export async function install(platform, engine, version) {
 
   let rubyPrefix
   if (common.shouldExtractInToolCache(engine, version)) {
-    rubyPrefix = common.getToolCacheRubyPrefix(version)
+    rubyPrefix = common.getToolCacheRubyPrefix(platform, version)
   } else {
     rubyPrefix = `${drive}:\\${base}`
   }