Lack of DynamicallyAccessedMemberTypes for any default constructor forces keeping unused types

[marek-safar]

One example is

runtime/src/mono/System.Private.CoreLib/src/System/RuntimeType.Mono.cs

Line 1838 in 72f5766

internal static object CreateInstanceForAnotherGenericParameter([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor | DynamicallyAccessedMemberTypes.NonPublicConstructors)] Type genericType, RuntimeType genericArgument)

which has an annotation for any constructor even if only the default constructor is considered. This keeps unnecessary dependencies like System.Runtime.Serialization.StreamingContext via EnumComparer<T> private ctors. I far as I know there is no workaround for this.

/cc @eerhardt @vitek-karas

[ghost]

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Issue Details

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One example is

runtime/src/mono/System.Private.CoreLib/src/System/RuntimeType.Mono.cs

Line 1838 in 72f5766

internal static object CreateInstanceForAnotherGenericParameter([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor | DynamicallyAccessedMemberTypes.NonPublicConstructors)] Type genericType, RuntimeType genericArgument)

which has an annotation for any constructor even if only the default constructor is considered. This keeps unnecessary dependencies like System.Runtime.Serialization.StreamingContext via EnumComparer<T> private ctors. I far as I know there is no workaround for this.

/cc @eerhardt @vitek-karas

Author:	marek-safar
Assignees:	-
Labels:	size-reduction
Milestone:	-

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[eerhardt]

Looking through all the callsites of CreateInstanceForAnotherGenericParameter, it looks like either all the types passed into it already have a public parameterless constructor, or they are internal classes, so we can make the constructor public on them.

The only one that doesn't look this way is

runtime/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/EqualityComparer.cs

Lines 180 to 183 in 82ca681

	// Needs to be public to support binary serialization compatibility
	public sealed partial class EnumEqualityComparer<T> : EqualityComparer<T>, ISerializable where T : struct, Enum
	{
	internal EnumEqualityComparer() { }

But that class isn't public in a contract - just in the implementation, and the comment indicates it needs to be public due to binary serialization. Since this isn't in a public contract, we could make its parameterless constructor public.

Then we can change CreateInstanceForAnotherGenericParameter implementation to only look for public parameterless constructors.

[marek-safar]

Then we can change CreateInstanceForAnotherGenericParameter implementation to only look for public parameterless constructors.

I guess that could work.

[eerhardt]

I can put up a PR after #50232 is merged.