Use better trimming message in ValidationContext

[eerhardt]

Add more details about why ValidationContext requires unreferenced code.

Fix #84324

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Issue Details

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Add more details about why ValidationContext requires unreferenced code.

Author:	eerhardt
Assignees:	-
Labels:	area-System.ComponentModel.DataAnnotations
Milestone:	-

[eerhardt]

The build is failing with

CP0015: (NETCORE_ENGINEERING_TELEMETRY=Build) Cannot change arguments of attribute 'System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute' on 'System.ComponentModel.DataAnnotations.ValidationContext.ValidationContext(object)'.

@ViktorHofer - is it possible to put RequiresUnreferencedCodeAttribute in a list that says it is not a breaking change to change the message of the attribute?

[ericstj]

is it possible to put RequiresUnreferencedCodeAttribute in a list that says it is not a breaking change to change the message of the attribute?

You can do that here: https://github.com/dotnet/runtime/blob/1145e01c0165b92f97fe77e616aa0cf755079b1c/eng/ApiCompatExcludeAttributes.txt

If you also want to exclude from the generation of reference assemblies, that should go here: https://github.com/dotnet/runtime/blob/1145e01c0165b92f97fe77e616aa0cf755079b1c/eng/DefaultGenApiDocIds.txt

[eerhardt]

You can do that here

Will this exclude the message or the whole attribute from being analyzed? Once an assembly is annotated, adding RequiresUnreferencedCode is kind of a breaking change (since you will start getting warnings in trimmed apps). But for libraries that haven't been annotated yet, we don't want it to complain (or would just baseline the api compat warning).

If it isn't possible to just exclude the message from the compat check, maybe we can just exclude the whole attribute for now.

If you also want to exclude from the generation of reference assemblies

Good to know. But we definitely want these in the ref assemblies.

[eerhardt]

Failure is #83655.