CS0649 not suppressed despite SuppressMessageAttribute

[Happypig375]

Version Used: VS16.5.1

Steps to Reproduce:

1. Clone https://github.com/verybadcat/CSharpMath with submodules
2. Open CSharpMath.sln
3. Open _Core folder -> CSharpMath.Rendering project -> _IgnoreTypographyWarnings.cs file
4. Build solution

Expected Behavior: CS0649 is suppressed like other warnings

Actual Behavior: SuppressMessageAttribute works for other warnings but not CS0649

[jcouv]

Looking at the compiler source code, I see:
// SuppressMessage attributes do not apply to compiler diagnostics.

I'm not sure where that is documented. I'm adding a note to docs (PR dotnet/dotnet-api-docs#4055) and closing this issue as by-design. Thanks