Bring back behavior of -Xfatal-warnings

[odersky]

Compiler version

Since #19245, -Xfatal-warning became completely useless to me. I critically rely on -Xfatal-warnings in connection with -Xprompt to stop the compilation at the point where a warning was given. I need this every other day. But with the new behavior, -Xfatal-warnings has become useless for this task, since it waits until the very end of the compilation run before anything is reported.

I don't see what the point of these disruptive things to the toolchain is. This change causes me to lose lots of time, and probably will cause problems for others relying on the old behavior as well.

We can institute new behavior for -Werror. But please, let's leave -Xfatal-warnings alone!

[dwijnand]

I can understand how it impedes your -Xprompt workflow (interesting to learn!). I definitely don't think we should diverge on behaviour between -Werror and -Xfatal-warnings. Ideally we can make -Xprompt react eagerly on a warning, while under fatal warnings.

[lrytz]

Workaround until then is using -Wconf:any:e instead of -Xfatal-warning.

[szymon-rd]

I don't see what the point of these disruptive things to the toolchain is

We decided to go in that direction because we wanted to make the flags enabling all the default errors (upcoming -W) usable with -Xfatal-warnings. Otherwise, the user would need to reiterate over his codebase multiple times, fixing the warnings, instead of seeing them all at once. That would make it a frustrating experience and negatively impact the DX. However, we can add an additional flag that makes the -Xfata-warnings fail early (or add an optional param to -Xfatal-warnings?)

[nicolasstucki]

It might be simpler to make -Werror and -Xfatal-warinings behave differently. -Werror could emmit the single error on warning, while -Xfatal-warinings could make every warning an error.

[lrytz]

I think that's what -Wconf:any:e is for. -Xfatal-warinings is the deprecated alias for -Werror.

But a bit of magic to turn -Werror into -Wconf:any:e when -Xprompt is enabled also seems reasonable.