Stencil dev server cacheDir stale cache invalidation strategy

Answer

Stencil’s dev server does not expose a built‑in flag or environment variable that automatically clears cacheDir when source files change; cached artifacts persist until the server restarts or the directory is manually deleted.

Confirmed facts

• No configuration option such as devServer.cacheDir or devServer.cacheInvalidate triggers automatic purging on file change.
• During stencil build --watch the server registers a chokidar watcher, rebuilds on each change, writes output to cacheDir (if caching is enabled), and does not remove existing entries.

Likely work‑arounds

• Setting devServer.cache: false (or assigning an empty string to cacheDir) disables the persistent cache, forcing each rebuild to write to a temporary location and effectively achieving immediate invalidation.
• The environment variable STENCIL_CACHE_DIR can override the cache directory; pointing it to a volatile OS‑temp folder that is cleared on each server start mimics invalidation, but the variable is read only at launch.
• A custom dev‑server plugin can listen to the fileChange event and call the internal cache‑clearing API (compiler.ctx.cache.clean()) to implement a user‑defined invalidation strategy.

Steps to enable automatic invalidation

1. Decide whether you can accept the rebuild‑latency cost of disabling the persistent cache.
2. If yes, add to your stencil.config.ts:

   export const config: Config = {
     devServer: {
       cache: false   // or cacheDir: ''
     }
   };
   

3. If you need to keep the cache for faster rebuilds, create a minimal plugin:

   export const cacheInvalidationPlugin = {
     name: 'cache-invalidation',
     devServer: {
       async fileChange(filePath, compilerCtx) {
         // internal API – may change in future Stencil releases
         if (compilerCtx?.cache?.clean) {
           await compilerCtx.cache.clean();
         }
       }
     }
   };
   

   and add it to the plugins array in stencil.config.ts.

Missing diagnostic detail

Are you able to tolerate the increased rebuild latency that results from disabling devServer.cache? Your answer determines whether the simple cache: false approach is suitable or whether a plugin‑based clean‑up is preferable.