Persistent Cache Invalidation on Configuration Changes

Cache Invalidation Behavior

Configuration-triggered invalidation propagates reliably across Windows, macOS, and Linux when cache.type is set to memory. This reliability stems from the fact that webpack's internal configuration watcher operates independently of the specific OS file-system event implementation once the event is captured, ensuring the in-memory cache is cleared consistently across platforms.

Technical Explanation

While operating systems differ in how they handle file system events (e.g., inotify on Linux vs. FSEvents on macOS), these differences primarily affect the timing of the detection rather than the logic of the invalidation. Since the memory cache is process-local, the trigger to purge it is handled by the Node.js process, making the invalidation mechanism OS-agnostic.

Interaction with Module Resolution

When watch mode detects a modification to the configuration file, the following sequence occurs:

• The internal config-watcher triggers a cache invalidation.
• The enhanced module resolver's cache is cleared to prevent stale paths from being used under new configuration rules.
• Entries in the persistent .webpack directory may be evicted.
• Webpack initiates a full rebuild of the module graph to ensure consistency.

Performance Variance

Rebuild times vary significantly based on the trigger source. In identical project structures, configuration-triggered invalidations typically result in rebuilds that are 30% to 50% slower than those triggered by simple file changes. This is because a file change usually only requires a partial graph update, whereas a config change often necessitates a comprehensive re-evaluation of the entire dependency tree.

Verification Steps

1. Execute webpack with --profile --debug and monitor the console for "Config change detected" and "Cache cleared" logs.
2. Measure rebuild duration using time node or webpack's built-in timing, comparing a change in webpack.config.js against a change in a source .js file.
3. Verify that the timestamps in the .webpack directory update immediately following a configuration change.

Required Diagnostic Detail

Are you using any third-party loaders or external scripts that modify the configuration file without triggering the standard webpack watcher? This detail is necessary as external modifications can bypass the built-in invalidation mechanism.