Provide updated cache when an error is thrown

[lukastaegert]

• Rollup Version: 1.31.0
• Operating System (or Browser): MacOS 10.13
• Node Version (if applicable): 12
• Link to reproduction (IMPORTANT, read below): https://gist.github.com/lukastaegert/ee3c064abf7e8aad862431ea69fb49a9

Expected Behavior

1. Run npm install; npm start.
   Rollup starts in watch mode and compiles successfully

2. Change app.ts to

   export function example(): number {
     return 42;
   }

   A type error is shown

3. Change app.ts back to its original state
   Rollup recompiles and the build is working again.

Actual Behavior

3. Change app.ts back to its original state
   Rollup recompiles but reuses a cached version of app.ts and displays the type error again.

This has been taken from rollup/plugins#186

The issue lies likely in how caching is handled in watch mode. The cache is only updated when a build completes successfully. When a module errors however, it should be evicted from the cache so that subsequent builds run it again. To solve this, maybe rollup can attach the cache to errors (similar to how watchFiles are added at the moment). Other options could be explored as well.

I do not think it is prudent to evict the entire cache on errors as this will mean a rebuild after an error will be unnecessarily slow while the user might be interested in a quick fix.

Instead of evicting erroring modules, we could also provide plugins with the option to manually evict modules from the cache. Still, the updated cache would need to be passed down to the caller of rollup.watch somehow.