Default IsDynamicCodeSupported feature switch to true for CoreCLR

[eerhardt]

With #80246, we added a feature switch for RuntimeFeature.IsDynamicCodeSupported. Previously when you published a trimmed CoreCLR app, RuntimeFeature.IsDynamicCodeSupported was hard-coded to true, so any logic switching on that property was eligible to be trimmed. For example:

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs

Lines 599 to 601 in b900a09

	RuntimeFeature.IsDynamicCodeSupported ?
	new ReflectionEmitCachingMemberAccessor() :
	new ReflectionMemberAccessor();

When you publish a CoreCLR trimmed app, the ReflectionMemberAccessor class could be trimmed. Now that we have a feature switch, the property is no longer a constant.

We could enable this by setting featuredefault=true in the ILLink.Substitutions.xml file, but that runs into the issue described in #96539.

This issue is to track enabling this for trimmed CoreCLR applications. It is blocked by #96539.

[ghost]

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Issue Details

---

With #80246, we added a feature switch for RuntimeFeature.IsDynamicCodeSupported. Previously when you published a trimmed CoreCLR app, RuntimeFeature.IsDynamicCodeSupported was hard-coded to true, so any logic switching on that property was eligible to be trimmed. For example:

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs

Lines 599 to 601 in b900a09

	RuntimeFeature.IsDynamicCodeSupported ?
	new ReflectionEmitCachingMemberAccessor() :
	new ReflectionMemberAccessor();

When you publish a CoreCLR trimmed app, the ReflectionMemberAccessor class could be trimmed. Now that we have a feature switch, the property is no longer a constant.

We could enable this by setting featuredefault=true in the ILLink.Substitutions.xml file, but that runs into the issue described in #96539.

This issue is to track enabling this for trimmed CoreCLR applications. It is blocked by #96539.

Author:	eerhardt
Assignees:	-
Labels:	area-System.Reflection.Emit, size-reduction
Milestone:	-

[steveharter]

@eerhardt is this still relevant for 8.0?

[ghost]

This issue has been marked needs-author-action and may be missing some important information.

[eerhardt]

@eerhardt is this still relevant for 8.0?

It is still relevant, but It is blocked by #96539.

[steveharter]

Moving to v9; assuming #96539 won't be done in v8.