Enable warnings as errors in CI pipeline

[MattKotsenas]

Would you be interested in turning on warnings as errors in the CI pipeline? When I build locally I see ~200 warnings, which makes ensuring I don't introduce new warnings difficult.

Some maintainers dislike the churn, so I wanted to ask before starting. If you agree, I'd follow an approach like this:

1. Enable warnings as errors in the AppVeyor pipeline, but not locally to avoid slowing down local dev when you're just trying to experiment
2. Fix all the warnings that can be easily / trivially fixed. I can break the fixes up by ID to make review easier
3. For issues that are difficult to fix, use inline suppressions to "baseline" and prevent future issues, and follow tracking bug(s) to address

[EdwardCooke]

That's interesting. When I build locally there's no errors or warnings. Same when the CI server builds, there's no warnings.

[MattKotsenas]

Interesting... I'll see if I can figure out what's causing the difference in behavior on my machine.

One thing that I notice is there's no global.json, so we're likely using different SDK versions. What SDK version do you / CI use?

[EdwardCooke]

I would assume the CI is using the latest. On mine I have 8.0.304. I ran the docker build, which is currently broken, just about to push up a PR for fixing that, and it shows a few.

[EdwardCooke]

K, the only warnings I could get to appear, which were some formatting and a file header, should be solved now. They also only showed up in Linux which I was able to get to them through the Docker image build.

[MattKotsenas]

OK, I'm running a 9.0-preview build. So I bet that coupled with opt-ing into "recommended" here:

YamlDotNet/YamlDotNet/YamlDotNet.csproj

Line 95 in aa9be23

<AnalysisLevel>latest-Recommended</AnalysisLevel>

means that the recommendations get stricter with the .NET 9 SDK.

I can just close this since this is just my problem. I also can make a quick PR with a global.json like this:

{
  "sdk": {
    "version": "8.0.300",
    "rollForward": "patch"
  }
}

(or similar). That would then signal to users what the acceptable SDK range is, pick the correct one if it's available, and give a (mostly) helpful error message if one isn't available.

Let me know what you prefer. Thanks!

[MattKotsenas]

OK, yeah verified with SquiggleCop that it's due to new warnings being recommended as part of .NET 9.

My personal preference is to use the global.json to set a version to help prevent people from getting into unsupported configurations, but I'm happy to do whatever you prefer :)

[EdwardCooke]

I think it would be beneficial to fix any warnings you’re getting with .net 9. We’ll eventually want to support it natively like we do with net6/net8. I think that would be my personal preference.

[lahma]

Created #971 to remove warnings on NET 9 SDK.

[EdwardCooke]

Thanks. I’ll hopefully get to the pr today or tomorrow.

[EdwardCooke]

Done. And errors are fixed. I enforced the code style checking on release builds (it added ~40 seconds) to the build and that's annoying so it'll do it during CI. Had to ignore a couple of IDE0055 Linux bugs and CRLF line endings but it's out now.

dotnet/roslyn#55526
dotnet/roslyn#73122