Request: Tweak the ILC error output to improve diagnosability

[jevansaks]

When turning on ILC's detailed error output (TrimmerSingleWarn=false), we get an output line per IL error which is great. But there's two tweaks I'd like to request:

1. Format the error output to align with MSBuild's error output.

Our build system filters output to errors of a particular format. It looks for almost all of the formats in https://learn.microsoft.com/en-us/visualstudio/msbuild/msbuild-diagnostic-format-for-tasks?view=vs-2022, but it expects the (line) or (line,col) for the origin. Thus, my request is that the IL errors be formatted not like:

ILC error IL1005: ...

But instead like:

ILC(0): error IL1005: ...

2. Provide the originating assembly for errors like IL1005

When we get IL1005 the message is only the originating namespace and method, but not the assembly. Especially in cases like C#/WinRT which generate source into your assembly in the same namespace, this leaves me hunting around for which assembly is having the problem. E.g.:

ILC error IL1005: WinRT.AuthoringMetadataTypeInitializer.GetMetadataTypeMapping(Type): Method will always throw because: Failed to load type 'X' from assembly 'Y'

If we could just add the originating assembly here, that would help a lot:

ILC error IL1005: AssemblyZZZ!WinRT.AuthoringMetadataTypeInitializer.GetMetadataTypeMapping(Type): Method will always throw because: Failed to load type 'X' from assembly 'Y'

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Tagging subscribers to this area: @agocke, @MichalStrehovsky, @jkotas
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[jkotas]

ILC(0)

(0) looks weird. There are many error messages produced by established tools for Windows that do not have the line numbers. For example, link test.obj produces LINK : fatal error LNK1181: cannot open input file 'test.obj'. Can we use formatting like that?

[jevansaks]

Yes, it looks like if there's a space after the tool name that will work, so could we do:

ILC : error IL1005: AssemblyZZZ!WinRT.AuthoringMetadataTypeInitializer.GetMetadataTypeMapping(Type): Method will always throw because: Failed to load type 'X' from assembly 'Y'