fix missing node_modules directory issue

snowpack/src/util.ts

@@ -2,6 +2,7 @@ import cacache from 'cacache';
 import globalCacheDir from 'cachedir';
 import etag from 'etag';
 import execa from 'execa';
+import crypto from 'crypto';
 import projectCacheDir from 'find-cache-dir';
 import findUp from 'find-up';
 import fs from 'fs';
@@ -25,7 +26,13 @@ export const GLOBAL_CACHE_DIR = globalCacheDir('snowpack');
 export const RESOURCE_CACHE = path.join(GLOBAL_CACHE_DIR, 'pkg-cache-1.4');
 export const BUILD_CACHE = path.join(GLOBAL_CACHE_DIR, 'build-cache-2.7');
 
-export const PROJECT_CACHE_DIR = projectCacheDir({name: 'snowpack'});
+export const PROJECT_CACHE_DIR =
+  projectCacheDir({name: 'snowpack'}) ||
+  // If `projectCacheDir()` is null, no node_modules directory exists.
+  // Use the current path (hashed) to create a cache entry in the global cache instead.
+  // Because this is specifically for dependencies, this fallback should rarely be used.
+  path.join(GLOBAL_CACHE_DIR, crypto.createHash('md5').update(process.cwd()).digest('hex'));
+
 export const DEV_DEPENDENCIES_DIR = path.join(PROJECT_CACHE_DIR, 'dev');
 const LOCKFILE_HASH_FILE = '.hash';