Fix Options Source Gen Trimming Issues

[tarekgh]

Fixes #92327

This change addresses issues that arise when using the Options source generator in AOT builds. The trimming linker generates warnings due to the use of Validation attributes that rely on reflection. Additionally, the source generator emits code that uses ValidationContext, which has constructors annotated with the RequiredUnreferencedCode attribute, leading to linker warnings. It's important to note that the ValidationContext object created in this context is exclusively used within the Validator.TryValidateValue API call.

The solution consists of two parts:

• We generate code to create the ValidationContext object and initialize the display and member names within it. This ensures the object's safe use because the reflection code path is not executed during this time. Consequently, we suppress the trimming linker warnings associated with this part.
• For attributes such as MaxLengthAttribute, MinLengthAttribute, LengthAttribute, CompareAttribute, and RangeAttribute, which rely on reflection, we generate replacement attributes. These replacement attributes are strongly typed and entirely avoid the use of reflection.

These changes address the issues and improve the overall safety and performance of the code in AOT buildings.

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Issue Details

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#92327

This change addresses issues that arise when using the Options source generator in AOT builds. The trimming linker generates warnings due to the use of Validation attributes that rely on reflection. Additionally, the source generator emits code that uses ValidationContext, which has constructors annotated with the RequiredUnreferencedCode attribute, leading to linker warnings. It's important to note that the ValidationContext object created in this context is exclusively used within the Validator.TryValidateValue API call.

The solution consists of two parts:

• We generate code to create the ValidationContext object and initialize the display and member names within it. This ensures the object's safe use because the reflection code path is not executed during this time. Consequently, we suppress the trimming linker warnings associated with this part.
• For attributes such as MaxLengthAttribute, MinLengthAttribute, LengthAttribute, CompareAttribute, and RangeAttribute, which rely on reflection, we generate replacement attributes. These replacement attributes are strongly typed and entirely avoid the use of reflection.

These changes address the issues and improve the overall safety and performance of the code in AOT buildings.

Author:	tarekgh
Assignees:	tarekgh
Labels:	area-Extensions-Options
Milestone:	-

[jeffhandley]

It's kind of a bummer that we have to special-case the built-in validators to pull this off, but it makes sense for .NET 8. This will address the vast majority of instances where AOT would have been blocked for customers. If we hear feedback about ecosystem or customer attributes that need this same type of substitution treatment, we can explore approaches for a general-purpose substitution.

[eiriktsarpalis]

I'm guessing this will be backported to 8?

[tarekgh]

I'm guessing this will be backported to 8?

Yes.

[jeffhandley]

Looks good to me, save @eiriktsarpalis's question about the target framework handling.

[tarekgh]

/backport to release/8.0

[github-actions]

Started backporting to release/8.0: https://github.com/dotnet/runtime/actions/runs/6450606563