Always check files recompilation by content

[mdesantis]

Fix #1439

[gauravtiwari]

Thanks @mdesantis 🍰

I am wondering if it would make sense to use mtime in development (in other words non-production environments) since here we can depend on mtime, which would be slightly faster.

[mdesantis]

@gauravtiwari I thought about that too but I'm worried about CI: it's unlikely that you run tests under production environment. What about doing CI env var check || env.production??

Also, an alternative fix could be just documenting the CI env var in the readme (and maybe renaming that; I don't think it's descriptive enough); developers might just be confused by the fact that this behaviour isn't written loud and clear

[latortuga]

As someone who is not super familiar with webpacker internals, forgive me if this is a dumb question. Is this codepath even used in development? My impression is that this feature is for when assets are precompiled, which doesn't happen in development mode.

[mdesantis]

@latortuga (not a Webpacker expert neither) but you can precompile assets even in development if for some reason you don't want to use webpack-dev-server, although it isn't very common I guess; and anyway you precompile them in test mode, if we are considering development as non-produciton

[swrobel]

I thought about that too but I'm worried about CI: it's unlikely that you run tests under production environment. What about doing CI env var check || env.production??

Please see @gauravtiwari's comment here for an example of what he means. Production & Test (or any env other than Development) would use the file hash method.

[jpickwell]

Is there a reason why the results of watched_files_digest isn't memoized? The function gets called once by stale? and again by record_compilation_digest (if stale? returns true) when calling compile.

[swrobel]

@jpickwell I raised this with my earlier PR and got the 👍 but didn't get around to implementing it.

[gauravtiwari]

Thanks everyone 🙏

Lets use mtime in development and file hash for other environments, where most likely we would be precompiling assets.

Why in development?

Mainly because, Webpacker ships with this "naive" on-demand compiler, which works well for simple cases and we don't want to slow it down, even if it's tiny by using file hash. If I am not missing anything, I think mtime should work fine there?

---

But as I wrote the above paragraph, I realised for simple cases using file hash wouldn't be slow either. So, perhaps just use file hash for everything to keep things simple?

[gauravtiwari]

Thanks @mdesantis :)

[gauravtiwari]

If you have sometime, could you also port this to 3-x-stable branch, please.

[kjleitz]

Any chance this will be put into 3.x? This fix would really help our deployment process out. Deployment went from 3-4 minutes to ~15 minutes for us. It's a big pain.

[latortuga]

@kjleitz looks like this got released on March 6, 2019: 8c25c09

🎉