dotnet-watch requires MtouchLink=None for iOS Simulator projects

[jonathanpeppers]

Description

dotnet watch does not work for iOS projects unless <MtouchLink>None</MtouchLink> is explicitly set in the .csproj file.

Without this setting, dotnet watch fails to work properly on iPhone Simulator builds.

Steps to Reproduce

1. Create a new .NET iOS project
2. Run dotnet watch targeting an iPhone Simulator
3. Observe that it does not work

Workaround

Add the following to your .csproj:

<PropertyGroup>
  <MtouchLink>None</MtouchLink>
</PropertyGroup>

Proposal

We should consider making MtouchLink=None the default for Debug iPhone Simulator builds, since linking is not typically needed in that configuration and it blocks dotnet watch from working.

This would improve the inner development loop experience without affecting Release or device builds.

[rolfbjarne]

Trimming is disabled for simulator builds only if the interpreter is enabled (otherwise the build takes forever), which IIRC is the default for MAUI builds (and Hot Reload doesn't work anyway unless the interpreter is enabled I believe),

macios/dotnet/targets/Xamarin.Shared.Sdk.Trimming.props

Line 68 in 3619b81

<_DefaultLinkMode Condition="'$(_DefaultLinkMode)' == '' And '$(_SdkIsSimulator)' == 'true' And (!$(RuntimeIdentifier.Contains('arm64')) Or '$(MtouchInterpreter)' != '')">None</_DefaultLinkMode>

Exactly which build configuration did you use? Was this just a 'dotnet new ios' or something else? Would you happen to have a binlog?

[dotnet-policy-service]

Hi @jonathanpeppers. We have added the "need-info" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[jonathanpeppers]

It was dotnet new ios, I can test again and get a .binlog.

[jonathanpeppers]

Sorry, it was a dotnet new maui project (.NET 11 Preview 4 builds), and if I don't set this property I get this exception in the startup hook:

Unhandled exception. System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
 ---> System.MissingMethodException: Method not found: 'System.String[] System.Environment.GetCommandLineArgs()'.
   at StartupHook.Initialize()
   at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)
   --- End of inner exception stack trace ---
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.StartupHookProvider.CallStartupHook(StartupHookNameOrPath startupHook)
   at System.StartupHookProvider.ProcessStartupHooks(String diagnosticStartupHooks)
   at System.StartupHookProvider.ManagedStartup(Char* pDiagnosticStartupHooks, Exception* pException)

Confusing, but related, I found these lines in dotnet/maui:

• https://github.com/dotnet/maui/blob/4c19ffb3935f15105df61e516f4eff546e9756d4/src/Controls/src/Build.Tasks/nuget/buildTransitive/netstandard2.0/Microsoft.Maui.Controls.Common.targets#L6-L11
• https://github.com/dotnet/maui/blob/4c19ffb3935f15105df61e516f4eff546e9756d4/src/Controls/src/Build.Tasks/nuget/buildTransitive/net6.0-ios10.0/Microsoft.Maui.Controls.iOS.targets#L4

[jonathanpeppers]

Oh, I forgot a .binlog:

Archive.zip

[rolfbjarne]

Oh, I forgot a .binlog:

Archive.zip

So MAUI does this:

<MtouchLink Condition="'$(MtouchLink)' == '' and '$(Configuration)' == 'Debug' and '$(UseMonoRuntime)' != 'true'">SdkOnly</MtouchLink>

It's turning on the trimmer when using CoreCLR.

This was implemented here: dotnet/maui#34107

[rolfbjarne]

I think this needs a change in MAUI as well.