Add JetBrains Annotations (useless from C# 8)

[YoshiRulz]

Includes NotNullAttribute/CanBeNullAttribute for design-time null checks by Rider, plus some other stuff. This is effectively a backport of nullable reference types from C# 8.

The package description claims "All usages of ReSharper Annotations attributes are erased from metadata by default, which means no actual binary reference to 'JetBrains.Annotations.dll' assembly is produced."

edit: consensus is that the benefits are too few, but I'm leaving this open as an extra nag to move to Framework 4.8.

[zeromus]

HOW would those annotations get erased from metadata? Does the nuget package add msbuild logic? Sounds rickety...

[vadosnaprimer]

I'm only fine with this if it can be disabled by default (or at least just locally). These links look relevant?
https://www.jetbrains.com/help/resharper/Reference_Options_Tools_Build_NuGet.html
https://stackoverflow.com/a/45445515/2792852

To explain my take, see the SO question for how much time it takes when nuget is heavily involved. And if we start one day, in a few years it will take just as much time (or more). So being able to avoid the overhead is valuable.

[YoshiRulz]

Checkout branch jb_annot_emuhawk to see what kind of effect this has on the build duration (it's based on e60896c).

[vadosnaprimer]

It took a few seconds to update the packages, but then everything kept building at normal speed, without nuget notifications. And it explicitly said fetching them upon build can be disabled. So until newer packages slow us down too much, it's fine.

[adelikat]

Not a fan of this. It is SO intrusive, for a not-free IDE that few people are using

[Scepheo]

HOW would those annotations get erased from metadata? Does the nuget package add msbuild logic? Sounds rickety...

To answer this: https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.conditionalattribute?view=netframework-4.8

[YoshiRulz]

First-party nullability is opt-in enabled in BizHawk.Common from 8de0355, and after #1801 will extend to more projects.
https://github.com/TASVideos/BizHawk/blob/4ed402fc59c5ebac072ce8888f62b09b50e0f085/BizHawk.Common/IImportResolver.cs#L11-L17