Mark error as build only

[CyrusNajmabadi]

Fixes #17259

[CyrusNajmabadi]

@dotnet/roslyn-compiler ptal.

[333fred]

I'd think I'd rather see us call GetEntryPointAndDiagnostics from GetDiagnostics, rather than marking this as a build-only error.

[333fred]

Also, please don't forget to test VB here, I assume something similar may exist.

[AlekseyTs]

I'd think I'd rather see us call GetEntryPointAndDiagnostics from GetDiagnostics, rather than marking this as a build-only error.

I will be fine if we start with making a simple change that reflects the current state of affairs with respect to when the error is reported. Changing at which compilation phase the error is reported could be done later if we have a strong case for that.

[333fred]

@AlekseyTs I'd argue that the original bug report is that case; @svick is confused why the error isn't showing up immediately. If that's not enough of a justification, then I don't know what would ever be enough of a justification.

[CyrusNajmabadi]

my concerns with GetEntryPointAndDiagnostics are:

1. is it expensive? i thought it would have to search the entire compilation
2. can it be called for the diagnostics for a particular file? i would think this was a question asked of the whole compilation.

[333fred]

1. Potentially, but since GetDiagnostics binds everything anyway, I don't really expect it to be that different.
2. I don't think so, no, it would only be whole project.

[AlekseyTs]

If that's not enough of a justification, then I don't know what would ever be enough of a justification.

Since the PR provided no explanation other than claiming that it fixed the issue, I assumed this change led to a desired IDE behavior. @CyrusNajmabadi could you please clarify?

[CyrusNajmabadi]

Since the PR provided no explanation other than claiming that it fixed the issue, I assumed this change led to a desired IDE behavior.

Yes. It addresses things where build errors are not filtered out when you go to 'build + intellisense' errors. Right now they are filtered out because we think this is a 'live' diagnostic, and thus we don't show the actual build diagnostic sincce we think it would cause duplicate errors.

[AlekseyTs]

Since the PR provided no explanation other than claiming that it fixed the issue, I assumed this change led to a desired IDE behavior.

Yes. It addresses things where build errors are not filtered out when you go to 'build + intellisense' errors. Right now they are filtered out because we think this is a 'live' diagnostic, and thus we don't show the actual build diagnostic sincce we think it would cause duplicate errors.

Sorry, it is still not clear to me. In your opinion, will the user remain confused after the change or not?

[CyrusNajmabadi]

I do not believe they will be confused.