ILLink shoud keep all metadata for rooted members

[jeromelaban]

Background and motivation

In relation to 166ceb8, #73241 and #74141, one possible avenue to allow for System.Text.Json to work with the IL Linker is to allow for metadata to be kept. The linker is currently trimming all metadata, regardless of the presence of the type in the trimmer root configuration file.

Exposing the Linker task's KeepMetadata:

runtime/src/tools/illink/src/ILLink.Tasks/LinkTask.cs

Line 226 in 4570167

public ITaskItem[] KeepMetadata { get; set; }

would allow an easier migration path without resorting to generated serializers.

API Proposal

<TrimmerKeepMetadata>all</TrimmerKeepMetadata>

API Usage

<TrimmerKeepMetadata>all</TrimmerKeepMetadata>

or

<TrimmerKeepMetadata>parametername</TrimmerKeepMetadata>

Alternative Designs

No response

Risks

I can't think of any, since not specifying the keep metadata is introducing more issues than it solves (even if it reduces the size impact of the linker)

[ghost]

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

Issue Details

---

Background and motivation

In relation to 166ceb8, #73241 and #74141, one possible avenue to allow for System.Text.Json to work with the IL Linker is to allow for metadata to be kept. The linker is currently trimming all metadata, regardless of the presence of the type in the trimmer root configuration file.

Exposing the Linker task's KeepMetadata:

runtime/src/tools/illink/src/ILLink.Tasks/LinkTask.cs

Line 226 in 4570167

public ITaskItem[] KeepMetadata { get; set; }

would allow an easier migration path without resorting to generated serializers.

API Proposal

<TrimmerKeepMetadata>all</TrimmerKeepMetadata>

API Usage

<TrimmerKeepMetadata>all</TrimmerKeepMetadata>

or

<TrimmerKeepMetadata>parametername</TrimmerKeepMetadata>

Alternative Designs

No response

Risks

I can't think of any, since not specifying the keep metadata is introducing more issues than it solves (even if it reduces the size impact of the linker)

Author:	jeromelaban
Assignees:	-
Labels:	api-suggestion, area-System.Reflection.Metadata
Milestone:	-

[teo-tsirpanis]

easier migration path without resorting to generated serializers

The migration path is exactly the one of the JSON source generator. Why can't you use it, and why don't trimmer root descriptors solve your problem?

[ghost]

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

Issue Details

---

Background and motivation

In relation to 166ceb8, #73241 and #74141, one possible avenue to allow for System.Text.Json to work with the IL Linker is to allow for metadata to be kept. The linker is currently trimming all metadata, regardless of the presence of the type in the trimmer root configuration file.

Exposing the Linker task's KeepMetadata:

runtime/src/tools/illink/src/ILLink.Tasks/LinkTask.cs

Line 226 in 4570167

public ITaskItem[] KeepMetadata { get; set; }

would allow an easier migration path without resorting to generated serializers.

API Proposal

<TrimmerKeepMetadata>all</TrimmerKeepMetadata>

API Usage

<TrimmerKeepMetadata>all</TrimmerKeepMetadata>

or

<TrimmerKeepMetadata>parametername</TrimmerKeepMetadata>

Alternative Designs

No response

Risks

I can't think of any, since not specifying the keep metadata is introducing more issues than it solves (even if it reduces the size impact of the linker)

Author:	jeromelaban
Assignees:	-
Labels:	api-suggestion, area-System.Text.Json, untriaged
Milestone:	-

[jeromelaban]

The migration path is exactly the one of the JSON source generator. Why can't you use it

Backward source compatibility with previous versions of .NET which do not have support for generators is one. Migration to later versions of .NET without changing code is about removing friction for developers.

and why don't trimmer root descriptors solve your problem?

Descriptors only impact types visibility, not metadata like parameters. This ILLink option is exactly about the scenario mentioned above.

The use case raising this proposal is for mobile apps using iOS/Android/Catalyst which require the use of the linker to not be large size regression from AOT-enabled Xamarin-based builds.

[MichalStrehovsky]

The linker is currently trimming all metadata, regardless of the presence of the type in the trimmer root configuration file.

Can you expand on this? Type that is specified as a root should not have the parameter names trimmed on any of its method. If it does, that's a trimming bug.

The only methods that can have parameter names trimmed are those that are not visible targets of reflection. Methods that are not visible targets of reflection are fair game to optimize. Trimming can: inline such method and delete it, rename such method, strip parameter names, etc. Removing parameter names is only one of the optimizations trimmings does (or will do in the future).

[ghost]

Tagging subscribers to this area: @agocke, @sbomer, @vitek-karas
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and motivation

In relation to 166ceb8, #73241 and #74141, one possible avenue to allow for System.Text.Json to work with the IL Linker is to allow for metadata to be kept. The linker is currently trimming all metadata, regardless of the presence of the type in the trimmer root configuration file.

Exposing the Linker task's KeepMetadata:

runtime/src/tools/illink/src/ILLink.Tasks/LinkTask.cs

Line 226 in 4570167

public ITaskItem[] KeepMetadata { get; set; }

would allow an easier migration path without resorting to generated serializers.

API Proposal

<TrimmerKeepMetadata>all</TrimmerKeepMetadata>

API Usage

<TrimmerKeepMetadata>all</TrimmerKeepMetadata>

or

<TrimmerKeepMetadata>parametername</TrimmerKeepMetadata>

Alternative Designs

No response

Risks

I can't think of any, since not specifying the keep metadata is introducing more issues than it solves (even if it reduces the size impact of the linker)

Author:	jeromelaban
Assignees:	-
Labels:	api-suggestion, untriaged, area-Tools-ILLink
Milestone:	-

[ghost]

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

[jeromelaban]

Can you expand on this? Type that is specified as a root should not have the parameter names trimmed on any of its method. If it does, that's a trimming bug.

The scenario is as follows. A record type present in a separate assembly, for which that full assembly is explicitly excluded in a TrimmerRootDescriptor definition file, has its constructor parameter names removed unless --keep-metadata all or --keep-metadata parametername is set on the linker parameters.

The Linker is running during the build of an net7.0-android or net7.0-ios app, though it's very likely that this behavior is the same for other targets.

[agocke]

@sbomer Is this the expected behavior? Do we trim parameter names even for assemblies that are preserved using TrimmerRootAssembly?

[sbomer]

I've confirmed the behavior - using a root descriptor doesn't prevent parameter names from being stripped. I agree with @MichalStrehovsky's comment in the sense that I think we should treat members rooted by descriptor as reflection-visible (we currently don't).

[HenriquecerMatos]

I have the same problem