Don't use the tool cache on GitHub-hosted runners by default

This introduces performance problems due to deficiencies in the
filesystem layout of GitHub-hosted runners; see #34. The tool cache
isn't very useful on such runners anyway, but I've added an option to
override the default.

Also add some more logging (related: #45).

Resolves: #34

action.yml

@@ -20,6 +20,10 @@ inputs:
     description: 'The maximum permitted size of the global Zig cache directory, in MiB. When the cache directory exceeds this size, it is cleared. Default is 2048 (2 GiB). 0 means no limit.'
     required: true
     default: 2048
+  use-tool-cache:
+    description: 'Override whether to use the tool cache when caching Zig installations. Default is false for GitHub-hosted runners, true for other runners.'
+    required: false
+    default: ''
 runs:
   using: 'node20'
   main: 'main.js'

common.js

@@ -32,7 +32,7 @@ async function getVersion() {
         return _cached_version;
       }
 
-      // Else, look for `mach_zig_version` first
+      // Else, look for `minimum_zig_version`
       match = MINIMUM_ZIG_VERSION_REGEX.exec(zon);
       if (match !== null) {
         _cached_version = match[1];

main.js

@@ -91,16 +91,41 @@ async function main() {
     // * 'cache' only caches the unextracted archive, but it does so across runs. It's a little
     //   less efficient, but still much preferable to fetching Zig from a mirror. We have this
     //   dependency anyway for caching the global Zig cache.
+    //
+    // Unfortunately, tool-cache can lead to serious performance problems on GitHub-hosted Actions
+    // runners -- or their Windows ones at least, because the tool cache is stored on a slow drive.
+    // There are even hacky workarounds for this in official Actions:
+    //
+    // https://github.com/actions/setup-go/blob/d35c59abb061a4a6fb18e82ac0862c26744d6ab5/src/installer.ts#L174
+    //
+    // Since tool-cache is only really useful on self-hosted runners, let's just disable it by
+    // default on GitHub-hosted runners, and hence execute Zig straight out of its extracted dir.
+    let use_tool_cache = core.getInput('use-tool-cache');
+    if (use_tool_cache === 'true') {
+      use_tool_cache = true;
+    } else if (use_tool_cache === 'false') {
+      use_tool_cache = false;
+    } else if (use_tool_cache === '') {
+      use_tool_cache = process.env['RUNNER_ENVIRONMENT'] !== 'github-hosted';
+    } else {
+      throw new Error("Invalid 'use-tool-cache' value. Valid values: 'true', 'false'");
+    }
+    core.info(`Using tool-cache: ${use_tool_cache}`);
 
-    let zig_dir = tc.find('zig', await common.getVersion());
-    if (!zig_dir) {
+    let zig_dir;
+    if (use_tool_cache) {
+      zig_dir = tc.find('zig', await common.getVersion());
+    }
+    if (zig_dir) {
+      core.info('Using cached Zig installation from tool-cache');
+    } else {
       const tarball_name = await common.getTarballName();
       const tarball_ext = await common.getTarballExt();
 
       core.info(`Fetching ${tarball_name}${tarball_ext}`);
       const fetch_start = Date.now();
       const tarball_path = await retrieveTarball(tarball_name, tarball_ext);
-      core.info(`fetch took ${Date.now() - fetch_start} ms`);
+      core.info(`Fetch took ${Date.now() - fetch_start} ms`);
 
       core.info(`Extracting tarball ${tarball_name}${tarball_ext}`);
 
@@ -108,10 +133,15 @@ async function main() {
       const zig_parent_dir = tarball_ext === '.zip' ?
         await tc.extractZip(tarball_path) :
         await tc.extractTar(tarball_path, null, 'xJ'); // J for xz
-      core.info(`extract took ${Date.now() - extract_start} ms`);
+      core.info(`Extract took ${Date.now() - extract_start} ms`);
 
       const zig_inner_dir = path.join(zig_parent_dir, tarball_name);
-      zig_dir = await tc.cacheDir(zig_inner_dir, 'zig', await common.getVersion());
+      if (use_tool_cache) {
+        core.info('Copying Zig installation to tool-cache');
+        zig_dir = await tc.cacheDir(zig_inner_dir, 'zig', await common.getVersion());
+      } else {
+        zig_dir = zig_inner_dir;
+      }
     }
 
     core.addPath(zig_dir);
@@ -120,6 +150,7 @@ async function main() {
     core.exportVariable('ZIG_LOCAL_CACHE_DIR', await common.getZigCachePath());
 
     if (core.getBooleanInput('use-cache')) {
+      core.info('Attempting restore of Zig cache');
       await cache.restoreCache([await common.getZigCachePath()], await common.getCachePrefix());
     }
   } catch (err) {

post.js

@@ -18,6 +18,7 @@ async function main() {
       }
 
       if (accessible) {
+        core.info('Checking cache size');
         const size = await totalSize(cache_path);
         const size_limit = core.getInput('cache-size-limit') * 1024 * 1024; // MiB -> bytes
         if (size_limit !== 0 && size > size_limit) {
@@ -26,10 +27,13 @@ async function main() {
           // remove the old cache entries, so we instead want to save an empty cache directory.
           // To do this, delete all the contents of the cache directory before saving the cache.
           await rmDirContents(cache_path);
+        } else {
+          core.info(`Cache directory is ${size} bytes, below limit of ${size_limit} bytes; keeping intact`);
         }
 
         const prefix = await common.getCachePrefix();
         const name = prefix + github.context.runId;
+        core.info('Saving Zig cache');
         await cache.saveCache([cache_path], name);
       }
     }