ILLink

[tranb3r]

ImageSharp is one of the biggest assemblies in my android app.
I've enabled dotnet trimmer (ILLink), but it only reduces the ImageSharp assembly size by ~30%.
I really have a basic usage (load an image, perform a simple computation on it), so I'm surprised the linker does not remove more code from ImageSharp.
Are you already aware of this issue?
Is there anything I can do to improve the efficency of the linker (for example, if I want to support only Png and drop all the other formats)?

[JimBobSquarePants]

Yes. Are you using the latest version? We recently did work that much reduced the binary size. #2514

[tranb3r]

Yes, I'm using the latest version.

I've tested several things but I can't figure out how to do it properly.

var img = Image.Load<Rgba32>(stream);
var img = Image.Load<Rgba32>(new DecoderOptions { Configuration = new() }, stream);
var img = Image.Load<Rgba32>(new DecoderOptions { Configuration = new Configuration(new PngConfigurationModule()) }, stream);
var img = PngDecoder.Instance.Decode<Rgba32>(new PngDecoderOptions { GeneralOptions = new DecoderOptions { Configuration = new() }}, stream);

Could you help me figuring out what is the proper implementation for loading a Png image from streamn (and being compliant with the trimmer)?

[tranb3r]

I've also tested a piece of code that I've seen here, but I don't get the same results: formats (bmp, gif, jpeg...) are not trimmed from the assembly.

[tranb3r]

I've spent a few more minutes on this and here is my conclusion.

The Configuration class contains this code that is not removed by the trimmer:

public static Configuration Default { get; } = Lazy.Value;

private static readonly Lazy<Configuration> Lazy = new Lazy<Configuration>(new Func<Configuration>(Configuration.CreateDefaultInstance));

internal static Configuration CreateDefaultInstance()
{
	return new Configuration(new IImageFormatConfigurationModule[]
	{
		new PngConfigurationModule(),
		new JpegConfigurationModule(),
		new GifConfigurationModule(),
		new BmpConfigurationModule(),
		new PbmConfigurationModule(),
		new TgaConfigurationModule(),
		new TiffConfigurationModule(),
		new WebpConfigurationModule(),
		new QoiConfigurationModule()
	});
}

[JimBobSquarePants]

I’ll re-check my output. Can’t remove the lazy evaluation without a major version though.

[JimBobSquarePants]

If you’re not getting the same results then you’re doing something different. I built that project and ran Sizoscope against it.

Could you share your results?

[JimBobSquarePants]

Thanks so much @MichalStrehovsky for your insight here and in the identification of the issue! You rock!

@tranb3r I am planning a major version this year but this is likely at least 6 months away as I’ve a huge amount of work to go through. It would, unfortunately, have to be a breaking change to workaround the issue pre .NET 9.

[tranb3r]

I understand.
I'll let you decide if you'd rather fix it in the future major version or wait for .net9.
Thanks to both of you for your help!

[MichalStrehovsky]

I think you can work around it with something along the lines of:

-private static readonly Lazy<Configuration> Lazy = new(CreateDefaultInstance);
+private static Lazy<Configuration> Lazy => LazyConfiguration.Lazy;
+
+static class LazyConfiguration
+{
+    internal static readonly Lazy<Configuration> Lazy = new(CreateDefaultInstance);
+}

I didn't actually try this but the issue is basically that right now, accessing an instance field brings in the static constructor on this class. Moving the expensive part into a separate class (with a separate static constructor) will work around because nobody is going to access the Lazy property on Configuration and the entire LazyConfiguration class should get trimmed.

[akoeplinger]

@tranb3r another workaround that you can try in your project is to use an ILLink substitution xml to replace the static constructor body with an empty stub:

Create a file called substitution.xml

<linker>
  <assembly fullname="SixLabors.ImageSharp">
    <type fullname="SixLabors.ImageSharp.Configuration">
      <method signature="System.Void .cctor()" body="stub" />
    </type>
  </assembly>
</linker>

And add the following to your .csproj:

<_ExtraTrimmerArgs>--substitutions substitution.xml</_ExtraTrimmerArgs>

[tranb3r]

Wow!! Thanks @akoeplinger, this is a great suggestion.
It totally works for me, without any change in ImageSharp or ILLink.

[MichalStrehovsky]

To be clear, this replaces the static constructor with an empty method. There will be no warning if at some point your use of ImageSharp needs this static constructor. Make sure you test your app well because your app would only be broken after trimming, not during F5 debugging.

[tranb3r]

Yes. Actually I'm already familiar with ILLink substitutions. Thanks.

[JimBobSquarePants]

@tranb3r if you fancy trying the code change suggested in a fork I can add it to the next bug fix release if successful.

[tranb3r]

@tranb3r if you fancy trying the code change suggested in a fork I can add it to the next bug fix release if successful.

The suggested code change does not work on my repro app.
I must be missing something...

[MichalStrehovsky]

If you have the ImageSharp library with the change, I can take a look.

[tranb3r]

You can review the change I've tested here: tranb3r@5f59edf
What looks wrong to me is that we still have this code in the Configuration class:
public static Configuration Default { get; } = Lazy.Value;