移除rails-observer后出现未初始化常量VideoObserver错误排查

Hey there, let’s break down why you’re seeing this intermittent NameError even after removing the rails-observer gem, deleting the VideoObserver model, and cleaning up related config. The error pointing to CoreExt::ActiveSupport.without_bootsnap_cache { super } gives us a big clue here—this is almost always tied to caching or leftover references that aren’t being consistently picked up by Rails’ loading system.

Common Causes #

• Bootsnap Caching Residue: Rails 5.2 uses Bootsnap by default to speed up constant loading. If VideoObserver was ever loaded into the cache, fragments of that constant might still linger in Bootsnap’s filesystem or memory cache. When Rails tries to resolve a reference (even an accidental one), it hits the stale cache, triggering the error. A refresh forces the cache to rebuild, which is why the error goes away temporarily.
• Uncleaned Implicit References: You might have leftover calls to VideoObserver hidden in less obvious places—like an initializer that sets up observer hooks, a model callback that references it indirectly, or even a comment that’s still being parsed by Rails’ autoloader. These references might only trigger under specific request conditions, causing the intermittent behavior.
• Rails Autoloader Quirks: Rails 5.2 uses the old classic autoloader (before Zeitwerk), which has edge cases around constant resolution. If there are leftover file fragments (like a partial VideoObserver.rb in a forgotten directory) or misconfigured autoload paths, the autoloader might occasionally try to load the constant even after you’ve deleted the model.

Fixes to Try #

• Purge Bootsnap and Rails Caches:
  • Run rails tmp:cache:clear to wipe Rails’ temporary cache.
  • Manually delete the tmp/cache/bootsnap directory to ensure Bootsnap’s specific cache is gone.
  • You can also run rm -rf tmp/* to clear all temporary files (pids, sockets, cache) entirely—this is safe and often fixes flaky caching issues.
• Search for Hidden References:
  • Run grep -r "VideoObserver" . from your project root to find every instance of the constant across all files (including initializers, models, views, and even config files). Delete any lines that reference it, even if they’re in comments or unused code.
• Verify Autoload Paths:
  • Check config/application.rb to make sure config.autoload_paths and config.eager_load_paths don’t include directories that once held VideoObserver (unless those directories are now empty).
• Restart Your Server:
  • Rails keeps loaded constants in memory while the server is running. A full restart will clear any lingering references to VideoObserver that are stuck in memory.

内容的提问来源于stack exchange，提问作者Runding Wang