scaladoc should pick up warning flags

[mkurz]

Is there a reason why the warning flags do not get used for Scaladoc?

scalaVersion := "3.3.0-RC3"
Compile / scalacOptions := Seq("-Werror", "-Wconf:any:error")

> Compile / doc
...
[info] Skipping unused scalacOptions: -Werror, -Wconf
...

In Scala 2.13 these flags do get used when compiling scaladoc (At least -Werror does)

If you don't want to support all of the warning flags for scaladoc, would it be at least possible to support at least -Werror/-Xfatal-warnings? That would be easy too by just moving the val XfatalWarnings... from line 161 from the WarningTrait into the CommonScalaSettings trait.

This PR is somehow similar #13233 / #13061

[mkurz]

Opened #17023 as well.

[mkurz]

Would highly appreciate feedback here or for #17023, thanks!

[dwijnand]

@som-snytt have you looked at the settings in Scala 3? Not sure how far they diverge from Scala 2. I think this PR looks ok to me.

[som-snytt]

CommonSettings predates me. I would be hard-pressed to explain why Scaladoc options are not a strict superset of the compiler options. I mean strict in the loose sense that accords with the mathematical. Some options may not do anything, but I'd hope the tool doesn't complain, except under -Vdebug or something. (And I know I can supply -Vdebug without it complaining for the same reason.)

Otherwise, I think the trait organization of the options is just a convenience, so mix'n'match at will.

[som-snytt]

Closing in favor of #17023, which is more narrow. Would lints or unused warnings apply to scaladoc? etc.