@nowarn annotation does not suppress any warnings (200USD Bounty)

[soufianexmx]

Using Scala 2.13, after upgrading to version 3.0.1, for a code like:

private def string[A: P]: P[String]   = P(CharIn("a-zA-Z0-9").rep(1).!)

we get compilation error:

@nowarn annotation does not suppress any warnings

Haoyi: To incentivize contribution, I'm putting a 200USD bounty on resolving this ticket. This is payable via bank transfer, and at my discretion in case of ambiguity. The acceptance criteria is a PR fixing this issue and updates to our test infrastructure to validate the fix

[limansky]

Same here. Reproduces both with Scala 2.13.10 and 3.2.2

[SethTisue]

presumably this started with https://github.com/com-lihaoyi/fastparse/pull/281

[SethTisue]

we get compilation error

well, presumably just a warning, that you have yourself promoted to an error with -Werror?

if someone is looking for a workaround, I think "@nowarn annotation does not suppress any warning" is itself a warning that can be suppressed with @nowarn?

[fanf]

I tried to add @nowarn("msg=@nowarn annotation does not suppress any warnings") (or generic @nowarn) at the class and method using macro level, and it does not suppress the warning (and add a new @nowarn annotation does not suppress any warnings)

[fanf]

I wasn't able to find an other way than disabling useless nowarn warning with -Wconf:cat=unused-nowarn:s (see https://www.scala-lang.org/api/current/scala/annotation/nowarn.html). I would prefer that scalac don't report nowarn inside macro, because as the user of the macro, I can't do anything about them.

[fanf]

So, one can selectively silent the problematic warning on specific file but keep them for other files with combined filter. For ex: -Wconf:cat=unused-nowarn&src=com/normation/utils/Version.scala:s,cat=unused-nowarn&src=com/normation/rudder/services/policies/InterpolatedValueCompiler.scala:s

Will silent the @nowarn annotation does not suppress any warnings warnings in com/normation/utils/Version.scala and com/normation/rudder/services/policies/InterpolatedValueCompiler.scala, but keep them in other files. More info with scala -Wconf:help

This is good enought for the time being for me.

[lihaoyi]

Somehow I'm not able to reproduce this inside my test suite. Would appreciate any help if someone wants to look into this inside the Fastparse repo and come up with a repro

[kitbellew]

@lihaoyi I don't know if this is related, but here's the error I got for 2.13.1 (and only that version): https://github.com/scalameta/scalameta/actions/runs/5503580335/jobs/10028930479?pr=3246

[lihaoyi]

Maybe it's specific to particular Scala versions? @soufianexmx @limansky @fanf what Scala versions are you guys seeing this in?

[Bathtor]

2.13.10 for me I think.

[fanf]

We first saw it in 2.13.10, and I checked it's still the case in 2.13.11

[limansky]

@lihaoyi I've tried with both 2.13.10 and 2.13.11. It looks like you have to have -Xlint in your scalacOptions.

[lihaoyi]

Ah I think it must be the -Xlint flag that I've been missing

[limansky]

@lihaoyi Hi, I've checked 3.0.2 and the issue is still there. Please let me know if you need minimal example to demonstrate the problem.

[He-Pin]

I'm using Fastparse too in a Java project, I would like to give this a try, this weekend.

[lihaoyi]

@He-Pin please go ahead!

[lihaoyi]

Should be fixed by https://github.com/com-lihaoyi/fastparse/pull/310

[SethTisue]

👏