[warn] Ignoring update of option -Xearly-tasty-output

[OlegYch]

Compiler version

3.8.0

Minimized example

set every usePipeling := true;Test/compile
in a multi-module sbt 1.12.0 build

Output Error/Warning message

[warn] Ignoring update of option -Xearly-tasty-output

Why this Error/Warning was not helpful

not sure what to do about it, pipelining seems to be working

[OlegYch]

apparently Test/scalacOptions sets -Ypickle-write twice in this case, not sure why it wasn't a problem in 3.7.4

[som-snytt]

It warns if it was set to a different value; usually last value wins, but for some settings, the previous value wins, so it will say "Ignoring".

It should be OK to set repeatedly to the same value. (I did not verify.)

[OlegYch]

it's apparently set once for compile and once for test:

Vector(
-Ypickle-java, -Ypickle-write, D:\api\target\scala-3.8.0\test-early\early.jar, 
-Ypickle-java, -Ypickle-write, D:\api\target\scala-3.8.0\early\early.jar
)

[som-snytt]

I see, -Ypickle-write aka -Xearly-tasty-output takes a file arg.

I suspect preferPrevious was added for this specific use case.

Edit: yes, support test scope by ignoring repeated pipelining flags.

Is it better not to warn? Edit: yes.

The purpose of the warning is to warn about misconfigured builds, since settings should be set once and correctly.

Maybe this use case could be fixed differently, or maybe settings should never warn but provide a diagnostic trace when requested. (It would be requested when a build breaks for a mysterious reason.)

Explained at https://github.com/scala/scala3/blob/main/sbt-test/pipelining/pipelining-test/test