[Mono] trim hot reload

[pavelsavara]

Trim Mono.HotReload classes when MetadataUpdaterSupport is false or not specified.

Related discussion #111215 (comment)

[dotnet-policy-service]

Tagging subscribers to 'size-reduction': @eerhardt, @SamMonoRT, @marek-safar
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[pavelsavara]

cc @MichalStrehovsky - this is separated from the timezones PR

[eerhardt]

Can you test that hot reload still works when you dotnet run (or dotnet watch) a project that has PublishAot/PublishTrimmed=true in the .csproj?

I think setting this property is going to break hot reload at debug time.

[MichalStrehovsky]

I tried:

using System.Runtime.CompilerServices;

while (true)
{
    Do();
    await Task.Delay(500);
}

[MethodImpl(MethodImplOptions.NoInlining)]
static void Do() => Console.WriteLine("Hello, World!");

with

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
	  <MetadataUpdaterSupport>false</MetadataUpdaterSupport>
  </PropertyGroup>

</Project>

With dotnet watch and then tried editing the Hello World string. The metadata does get updated. Did I miss some step?

[eerhardt]

Try using something that uses MetadataUpdater.IsSupported:

https://source.dot.net/#System.Private.CoreLib/src/System/Reflection/Metadata/MetadataUpdater.cs,ed8a7ebb4c4b1bc6,references

Like Blazor WASM.

See also - #57143 (comment).

[MichalStrehovsky]

using System.Reflection.Metadata;

Console.WriteLine(MetadataUpdater.IsSupported);

This will print False with dotnet run (irrespective of MetadataUpdaterSupport value) and True with dotnet watch (again, irrespective of the property). This still matches my expectations.