Bug: EquatablePortableExecutableReference throws FileNotFoundException

[chsienki]

Description

EquatablePortableExecutableReference calls .GetMetadataId() to determine if two references are the same:

CsWinRT/src/Authoring/WinRT.SourceGenerator/RcwReflectionFallbackGenerator.cs

Line 334 in b1733e9

return other.Reference.GetMetadataId() == Reference.GetMetadataId();

However, in the IDE it's possible that a reference is a MissingMetadataReference. This will unconditionally throw a FileNotFoundException :

https://github.com/dotnet/roslyn/blob/23f8f05fd7ac83e79907096ac5fed533138f10b7/src/Workspaces/Core/Portable/Serialization/SerializerService_Reference.cs#L531

The generator should guard against this condition instead of crashing.

Steps To Reproduce

An example of this issue is captured here, including an internal only accessible memory dump of when the issue occurs https://developercommunity.visualstudio.com/t/Feature-X-is-currently-unavailable-due-t/10803095

Expected Behavior

The generator should not crash.

Version Info

Latest

Additional Context

No response

[manodasanW]

@chsienki Is there a trivial way to create a scenario where the reference is a MissingMetadataReference to confirm the fix works?