Dig deeper into Vite's HMR problems

[sodic]

We had some Vite HMR problems and fixed them by introducing the incremental option to the TS compiler. Context:

• Fix Vite HMR #1829
• Updates SDK tsconfig to enable the incremental #1931

Here's a high-level overview of the relationship between Vite's HMR and our SDK (node_modules/wasp):

• We want Vite to watch node_modules/wasp. If it didn't, we'd have to rerun wasp start on every significant change.
• On the other hand, we don't want Vite to clear the web app's state and do a full site refresh unless necessary.

By default, TypeScript updates all output files regardless of whether they change or not. Also, Vite (again by default) decides whether to perform a refresh based on files' timestamps. Together, these two behaviors resulted in many redundant site refreshes.

Possible solutions:

1. The best solution would be making Vite smarter when detecting changes (for example, by comparing file hashes instead of their timestamps).
2. If that isn't possible, the second-best solution would be preventing TypeScript from updating unchaged output files, which can be done with the incremental compiler option.

Since redundant refreshes and output noise proved frustrating to our users, #1931 implemented the second option (incremental updates). This had a nice side effect of speeding up the SDK build.

We didn't have time to properly explore the first option (smart changes detection)

Therefore, we should

• Explore the possibility of making Vite smarter about deciding when to refresh.
• Figure out why this guy claims that it isn't possible to watch a locally linked package when it seems that it's not only possible but also unavoidable? Have we missed something?