Fallbacks to /tmp if the preferred cache folder isn't writable

Author: Maël Nison

src/config.js

@@ -276,9 +276,27 @@ export default class Config {
       networkConcurrency: this.networkConcurrency,
       networkTimeout: this.networkTimeout,
     });
-    this._cacheRootFolder = String(
-      opts.cacheFolder || this.getOption('cache-folder', true) || constants.MODULE_CACHE_DIRECTORY,
-    );
+
+    let cacheRootFolder = opts.cacheFolder || this.getOption('cache-folder', true);
+
+    for (let t = 0; t < constants.PREFERRED_MODULE_CACHE_DIRECTORIES.length && !cacheRootFolder; ++t) {
+      const tentativeCacheFolder = constants.PREFERRED_MODULE_CACHE_DIRECTORIES[t];
+
+      try {
+        await fs.mkdirp(tentativeCacheFolder);
+        await fs.writeFile(path.join(tentativeCacheFolder, constants.WTEST_FILENAME), `testing write access`);
+        cacheRootFolder = tentativeCacheFolder;
+      } catch (error) {
+        this.reporter.warn(this.reporter.lang('cacheFolderSkipped', tentativeCacheFolder));
+      }
+    }
+
+    if (!cacheRootFolder) {
+      throw new MessageError(this.reporter.lang('cacheFolderMissing'));
+    } else {
+      this._cacheRootFolder = String(cacheRootFolder);
+    }
+
     this.workspacesEnabled = Boolean(this.getOption('workspaces-experimental'));
 
     this.pruneOfflineMirror = Boolean(this.getOption('yarn-offline-mirror-pruning'));

src/constants.js

@@ -46,15 +46,21 @@ function getDirectory(category: string): string {
   return path.join(userHome, `.${category}`, 'yarn');
 }
 
-function getCacheDirectory(): string {
+function getPreferredCacheDirectories(): Array<string> {
+  const preferredCacheDirectories = [getDirectory('cache')];
+
+  if (process.platform !== 'win32') {
+    preferredCacheDirectories.unshift('/tmp/.yarn-cache');
+  }
+
   if (process.platform === 'darwin') {
-    return path.join(userHome, 'Library', 'Caches', 'Yarn');
+    preferredCacheDirectories.unshift(path.join(userHome, 'Library', 'Caches', 'Yarn'));
   }
 
-  return getDirectory('cache');
+  return preferredCacheDirectories;
 }
 
-export const MODULE_CACHE_DIRECTORY = getCacheDirectory();
+export const PREFERRED_MODULE_CACHE_DIRECTORIES = getPreferredCacheDirectories();
 export const CONFIG_DIRECTORY = getDirectory('config');
 export const LINK_REGISTRY_DIRECTORY = path.join(CONFIG_DIRECTORY, 'link');
 export const GLOBAL_MODULE_DIRECTORY = path.join(CONFIG_DIRECTORY, 'global');
@@ -68,6 +74,7 @@ export const LOCKFILE_FILENAME = 'yarn.lock';
 export const METADATA_FILENAME = '.yarn-metadata.json';
 export const TARBALL_FILENAME = '.yarn-tarball.tgz';
 export const CLEAN_FILENAME = '.yarnclean';
+export const WTEST_FILENAME = 'yarn-wtest';
 
 export const DEFAULT_INDENT = '  ';
 export const SINGLE_INSTANCE_PORT = 31997;

src/reporters/lang/en.js

@@ -174,6 +174,9 @@ const messages = {
   workspaceNameMandatory: 'Missing name in workspace at $0, ignoring.',
   workspaceNameDuplicate: 'There are more than one workspace with name $0',
 
+  cacheFolderSkipped: 'Skipping preferred cache folder $0 because it is not writable.',
+  cacheFolderMissing: "Yarn hasn't been able to find a cache folder. Please use an explicit --cache-folder option to tell it what location to use, or make one of the preferred locations writable.",
+
   execMissingCommand: 'Missing command name.',
 
   commandNotSpecified: 'No command specified.',