Annotate XslCompiledTransform as RequiresDynamicCode.

[eerhardt]

Related: #84389.

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[ghost]

Tagging subscribers to this area: @dotnet/area-system-xml
See info in area-owners.md if you want to be subscribed.

Issue Details

---

null

Author:	eerhardt
Assignees:	-
Labels:	area-System.Xml
Milestone:	-

[eerhardt]

@vitek-karas @agocke @jkotas @MichalStrehovsky -

This is a really unfortunate case that I'm not sure how to handle. It started with marking XslCompiledTransform as RequiresDynamicCode. That meant that System.Security.Cryptography.Xml needed to be marked as RequiresDynamicCode in the off-chance that XSLTs are used in the XML payload. Which then infected Microsoft.Extensions.Configuration.Xml in the off-chance that the XML files were using EncryptedXml. At each level up the chances that the caller is using XSLTs are smaller and smaller.

The good thing is that Microsoft.Extensions.Configuration.Xml isn't used in many mainline scenarios, but it still concerns me having to mark these APIs as unsafe, when 95+% of callers aren't going to have problems. It might make people numb to these warnings if they are for rarely used capabilities.

Do we have a strategy on when warnings can be suppressed in cases like this? Or is it a strict "it is guaranteed to work, or will warn" policy?

[jkotas]

The usual strategy we have developed for cases like this is to introduce a config switch and default it to false when PublishTrimmed / PublishAot is on. I think Microsoft.Extensions.Configuration.Xml would be the most meaningful place for such config switch.

[eerhardt]

Thanks. For this case I'll wait for customer feedback before adding a feature switch in this area. The same APIs are getting annotated with RequiresUnreferencedCode in #84468. The switch will have to disable using EncryptXml altogether. It may not be worth adding the switch if no one is using Xml Configuration in trimmed/AOT'd apps, or if they are satisfied with suppressing the warning. At least they will see up front that using encrypted XML isn't guaranteed to work.