[BUG] AOT compile fails for iOS MAUI

[J-Swift]

Describe the bug

I'm unable to build an AOT release build for iOS MAUI with ReactiveUI v17.1.17. Building with verbose gives me this

Failed to load method 0x6000472 from '[...]/obj/iPhone/Release/net6.0-ios/ios-arm64/linked/ReactiveUI.dll' due to Could not resolve signature of method ReactiveUI.ReactiveCollectionViewSource`1[TSource]:NumberOfSections.
Mono Ahead of Time compiler - compiling assembly [...]/obj/iPhone/Release/net6.0-ios/ios-arm64/linked/ReactiveUI.dll
Run with MONO_LOG_LEVEL=debug for more information.
AOTID 765DC80D-F50C-E335-7D3F-74B08B59D889
AOT of image [...]/obj/iPhone/Release/net6.0-ios/ios-arm64/linked/ReactiveUI.dll failed.
Could not load signature of ReactiveUI.ReactiveCollectionViewSource`1[TSource]:NumberOfSections due to: Could not resolve type with token 010000b4 from typeref (expected class 'System.nint' in assembly 'Xamarin.iOS, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065') assembly:Xamarin.iOS, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065 type:System.nint member:(null)

Steps To Reproduce

Not sure on a repro just yet, but it fails for me when doing the following build:

dotnet build MyApp -t:Build -c:Release -f:net6.0-ios -p:Platform=iPhone -p:RuntimeIdentifier=ios-arm64 \
    -p:BuildIpa=True -p:OutputPath='bin/Simulator/' -p:TreatWarningsAsErrors=True

Expected behaviour

AOT compile works

Environment

• OS: macOS
• Version 12.2
• Device: intel-chip macbook pro
• ReactiveUI Version: 17.7.17

Additional context

dotnet version: 6.0.200 (installed via daily https://aka.ms/dotnet/6.0.2xx/daily/dotnet-sdk-osx-x64.pkg)
xcode version: 13.2.1
MAUI version: preview 12

I installed the MAUI workload like this

sudo dotnet workload install maui --from-rollback-file https://aka.ms/dotnet/maui/preview.12.json \
    --source https://aka.ms/dotnet6/nuget/index.json  --source https://api.nuget.org/v3/index.json

[glennawatson]

There's been some breaking changes in a recent version of Maui that we need to adapt to. Joys of supporting preview libraries.

We'll be doing another Maui release this week for our library to grab the latest changes.

Thanks for the issue.

[J-Swift]

No worries, I figured as much. I'm well aware of the joys of targeting a preview 😄. When I poked around it seemed to me you already were compliant w/ the nint change so I wasn't sure if this was a regression or not.

I appreciate the time you put into the library!

[glennawatson]

Try the latest sub-release. Haven't done much other than let it use the latest maui version to compile.

[J-Swift]

Just did a quick rebuild and it seems to still have the same issue. I'll give it a look tomorrow to see if theres any workarounds (or wait until preview 13 hits which I estimate should be soonish).

[J-Swift]

OK I lied, I did a quick extra test and tried to workaround any stripping that might be happening...

This code

var x = new ReactiveUI.ReactiveCollectionViewSource<int>(null);
var _ = x.NumberOfSections(null);

Gives

 error CS7069: Reference to type 'nint' claims it is defined in 'Xamarin.iOS', but it could not be found

now I'm stopping until tomorrow to look further : )

[J-Swift]

OK, so Monday update.

I saw you put out 17.1.50. Tried that out and unfortunately its the same issue as before.

I found a possible workaround though, so maybe it will guide what the issue might be. I was able to download and reference ReactiveUI directly and build that way. I had to do a couple things though to make the build work:

• Set my apps TargetFrameworks to net6.0;net6.0-ios (previously this was net6.0-android;net6.0-ios. The IL stripping failed if I didn't include net6.0.
• Set TargetFrameworks in ReactiveUI/ReactiveUI.csproj to net6.0;net6.0-ios, otherwise build will fail because it lists a bunch of unknown frameworks (e.g. tvOS)
• Remove ReactiveUI.Fody and ReactiveUI from my references, and handwrite the helpers. Not sure what the issue with Fody was here.

So, my csproj references changed from

  <ItemGroup>
    <PackageReference Include="ReactiveUI" Version="17.1.50" />
    <PackageReference Include="ReactiveUI.Fody" Version="17.1.50" />
    <PackageReference Include="ReactiveUI.Maui" Version="17.1.50" />
  </ItemGroup>

to

  <ItemGroup>
    <ProjectReference Include="..\ReactiveUI\src\ReactiveUI.Maui\ReactiveUI.Maui.csproj" />
  </ItemGroup> 

This lets me generate and install an ipa file to a device locally, though I haven't tested on Testflight yet. I also had a weird bug where this suddenly didn't work, and the app would crash at runtime without AOT errors reported. I still don't know what happened but it seems a rm -rf {bin,obj} and rebuild eventually fixed it.

[J-Swift]

Also note, I tried generating the DLLs locally and referencing them with HintPath, but it gives the same AOT errors.

[glennawatson]

Yeah I'm likely at this stage just going to tag some Microsoft people into this issue on the Maui team and see if they can help on this one.

[J-Swift]

For what its worth, I asked about it in the dotnet discord today but didn't get any input (https://discord.com/channels/732297728826277939/732297808148824115/942818712703107122). You probably know better than me who/where to ask though

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[PureWeen]

@rolfbjarne thoughts?

@J-Swift you might also try uninstalling the daily dotnet sdk. Just use the dotnet sdk that's installed with the Visual Studio 2022 Public Preview

[rolfbjarne]

This is due to the breaking changes we're doing; everything needs to be using the same version of MAUI and the underlying iOS workload for things to work.

Try the latest sub-release. Haven't done much other than let it use the latest maui version to compile.

Exactly which maui version was this?

[J-Swift]

you might also try uninstalling the daily dotnet sdk. Just use the dotnet sdk that's installed with the Visual Studio 2022 Public Preview

@PureWeen Im not sure that will work since this is on a mac right? Im trying to avoid bringing VS for mac into this because it seemed to have messed some other things up when I installed it.

everything needs to be using the same version of MAUI and the underlying iOS workload for things to work

@rolfbjarne should I be able to generate a DLL on my machine and reference it with HintPath in that case? I tried that during the investigation and it gave the same AOT errors, but maybe I wasn't passing the right command to create the DLL? I'm ignorant to that process so definitely possible I wasn't using the right flags, etc

[rolfbjarne]

everything needs to be using the same version of MAUI and the underlying iOS workload for things to work

@rolfbjarne should I be able to generate a DLL on my machine and reference it with HintPath in that case? I tried that during the investigation and it gave the same AOT errors, but maybe I wasn't passing the right command to create the DLL? I'm ignorant to that process so definitely possible I wasn't using the right flags, etc

You mean you want to build ReactiveUI locally, and then reference that using HintPath in your project file?

I don't see why it shouldn't be possible to make that work (although it never is as simple as you'd think)

[J-Swift]

Well I dont want to : D I'm just saying I tried to do that at one point and it gave AOT errors, same as if it got generated by glenn. So I wasn't sure it was due to mismatch of toolchains/workloads since I was on the same machine that generated the DLL and had the same issue.

In any case, I was able to get the minimal repro yesterday so I'll work on getting that pushed just so we are all on the same page of the circumstances.