set Zig cache directories to the workspace-local .zig-cache

This accomplishes two things:

* It prevents unbounded growth in disk space usage on self-hosted runners.
* It prevents races with other jobs when clearing the cache.

README.md

@@ -55,7 +55,7 @@ be https://ziglang.org/download to avoid the official website being hit with lar
 If you've experienced issues with a default mirror, please [open an issue][report-bad-mirror] on the Zig
 website repository, which is where the list of mirrors is maintained.
 
-If necessary, the caching of the global Zig cache directory can be disabled by setting the option
+If necessary, the caching of the global and local Zig cache directories can be disabled by setting the option
 `use-cache: false`. Don't do this without reason: preserving the Zig cache will typically speed things up
 and decrease the load on your Actions runners.
 

action.yml

@@ -9,7 +9,7 @@ inputs:
     required: false
     default: ''
   use-cache:
-    description: 'Whether to cache the global Zig cache directory.'
+    description: 'Whether to cache the global and local Zig cache directories.'
     required: true
     default: true
   cache-key:

common.js

@@ -16,9 +16,6 @@ const CACHE_PREFIX = "setup-zig-global-cache-";
 // See: https://github.com/marler8997/anyzig?tab=readme-ov-file#mach-versions-and-download-mirror
 const MACH_ZIG_VERSION_REGEX = /\.\s*mach_zig_version\s*=\s*"(.*?)"/;
 const MINIMUM_ZIG_VERSION_REGEX = /\.\s*minimum_zig_version\s*=\s*"(.*?)"/;
-// This is tied quite precisely to the output of `zig env`. It's just a temporary workaround until
-// I get around to implementing a ZON parser here.
-const ZIG_ENV_CACHE_DIR_REGEX = /^\s*\.global_cache_dir = "(.*)",$/m;
 
 let _cached_version = null;
 async function getVersion() {
@@ -203,50 +200,11 @@ async function getCachePrefix() {
   const job_name = github.context.job.replaceAll(/[^\w]/g, "_");
   const user_key = core.getInput('cache-key');
 
-  return `setup-zig-cache-${job_name}-${tarball_name}-${user_key}-`;
+  return `setup-zig-cache-v2-${job_name}-${tarball_name}-${user_key}-`;
 }
 
-async function getZigCachePath() {
-  const env_zon = (await exec.getExecOutput('zig', ['env'])).stdout;
-  if (env_zon[0] !== '.') {
-    // JSON (legacy)
-    return JSON.parse(env_zon)['global_cache_dir'];
-  }
-  const match = ZIG_ENV_CACHE_DIR_REGEX.exec(env_zon);
-  if (!match) throw new Error("Failed to parse cache directory from 'zig env' output");
-  return parseZigString(match[1]);
-}
-function parseZigString(raw) {
-  // This function is neither complete (Unicode codepoint literals), nor correct (byte-escapes
-  // aren't really compatible with JS "strings"). It's just a temporary best-effort implementation
-  // which can hopefully handle any real-world directory path we encounter.
-  let result = "";
-  let i = 0;
-  while (i < raw.length) {
-    if (raw[i] != '\\') {
-      result += raw[i];
-      i += 1;
-      continue;
-    }
-    i += 2;
-    switch (raw[i - 1]) {
-      case 'n': result += '\n'; break;
-      case 'r': result += '\r'; break;
-      case '\\': result += '\\'; break;
-      case 't': result += '\t'; break;
-      case '\'': result += '\''; break;
-      case '"': result += '"'; break;
-      case 'x': {
-        const byte_val = parseInt(raw.slice(i, i + 2), 16);
-        result += String.fromCharCode(byte_val);
-        i += 2;
-        break;
-      }
-      case 'u': throw new Error("unsupported Unicode codepoint literal in string");
-      default: throw new Error("invalid escape code in string");
-    }
-  }
-  return result;
+function getZigCachePath() {
+  return path.join(process.env['GITHUB_WORKSPACE'] ?? process.cwd(), '.zig-cache');
 }
 
 module.exports = {

main.js

@@ -162,12 +162,13 @@ async function main() {
 
     core.addPath(zig_dir);
 
-    // Direct Zig to use the global cache as every local cache, so that we get maximum benefit from the caching below.
-    core.exportVariable('ZIG_LOCAL_CACHE_DIR', await common.getZigCachePath());
+    const cache_path = common.getZigCachePath();
+    core.exportVariable('ZIG_GLOBAL_CACHE_DIR', cache_path);
+    core.exportVariable('ZIG_LOCAL_CACHE_DIR', cache_path);
 
     if (core.getBooleanInput('use-cache')) {
       core.info('Attempting restore of Zig cache');
-      await cache.restoreCache([await common.getZigCachePath()], await common.getCachePrefix());
+      await cache.restoreCache([cache_path], await common.getCachePrefix());
     }
   } catch (err) {
     core.setFailed(err.message);