Scoped nowarn

[Martin521]

Description

Implements Scoped Nowarn according to draft RFC FS-1146.

This PR has taken a while. I had to deal with much more complexity than I imagined when I naively volunteered to tackle the feature request. Anyway, here we are.

I have split the PR into 7 commits that can be reviewed in sequence.
All of them compile, 1 and 4 - 7 also pass all tests locally.

1. Add the feature flag, baseline tests, and the core WarnScopes module. See src/Compiler/SyntaxTree/WarnScopes.fsi and the RFC for the functionality of the module.

2. Add the necessary changes to lexing and parsing. Note that the warn directives can no longer be collected during parsing (since they can now appear not only in top-level modules, but anywhere). So we collect them during lexing, similar to the processing of #if/#else/#endif directives.

3. Remove legacy #nowarn processing (but hold off AST changes)

4. Integrate the WarnScopes functionality and test it

5. Add warn directive trivia (but hold off AST changes)

6. Enable warn directive trivia (which means AST changes)

7. Remove defunct types and parameters related to former #nowarn processing (more AST changes)

There is also a separate commit for the IlVerify baseline updates (change in line numbers only)

Checklist

• Test cases added
• Performance benchmarks added in case of performance changes
• Release notes entry updated
• Create documentation update PRs (see RFC)

[github-actions]

❗ Release notes required

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✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/9.0.300.md
LanguageFeatures.fsi	docs/release-notes/.Language/preview.md

[psfinaki]

Hi @Martin521 - thanks for the contribution. It's a substantial effort and we appreciate it. The PR is on our radar - just keep in mind that it's big and specific, and it will take time to find capacity for it.

If anyone from the community gets to thoroughly review it, that would be valuable as well.

Thanks for your diligence and patience :)

[psfinaki]

Hi @Martin521 and sorry this has been taking forever! I know you're patient but we shouldn't exercise your patience too much :)

We've discussed this PR within the team. In generally, we're in favor of having this in - it's a valuable improvement. That said, since the PR touches a few important places, we should be very sure that we don't compromise the compiler design and VS functionality. It's not that both are perfect but you know - the boy scout rule.

I added a few notes in accord with this - let's iterate here a bit and refine the changes.

[psfinaki]

Hi @Martin521. We've discussed this PR with the team yesterday. We are still on our low capacities but we don't want the PR to get stale, so we're thinking how to move on here.

I resolved a few comments which were duplicates or were addressed. I kept a few where we still have some "uncanny feelings". You know, not very happy and confident but also without an immediate idea on how to make things better. Also, some comments mention that you've wanted to look at other options, so please comment on those.

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Let me ask you a few possibly annoying questions. Annoying because they might have popped up in some discussions already, but we want to summarize things a bit.

1. Do you consider any changes here breaking by any definition of breaking? (Fixing deep long-standing bugs might sometimes qualify...)

2. What parts of the compiler code are changes beyond propagation of the function parameters etc.? And how does the PR ensure that nothing breaks in that sense? Can you think of any testing there on top of what you've already added?

3. We respect the fact you don't have Visual Studio for testing the feature - that said, in principle, what do you think should be tested to be sure things work there and in other editors? I did some smoke testing yesterday in my VS (successfully) but I might have missed some scenarios. We might set up some sort of community session to try things out or brainstorm things a bit.

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Thanks for your patience.

[Martin521]

Let me ask you a few possibly annoying questions.

Nothing annoying here. I will tackle the questions and also the open comments one by one in the coming days.