[Question] TextTransformation compiles but fails when running with a method not found exception?

[joaofpereira]

Hello all!

I tried to use Mono T4 to create some complex templates, but I found a problem.
I created a minimal example that reproduces the problem found, which I present now.

The .csproj is named Example.csproj:

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

  <PropertyGroup>
    <TargetFrameworks>net48;net7.0</TargetFrameworks>
    <PlatformTargets>x86;x64</PlatformTargets>
  </PropertyGroup>

</Project>

On my simple class I just created a property to get and set it:

namespace Example
{
    public class Helper
    {
        public System.Func<System.Uri, System.Xml.XmlReader> FuncProperty {get;set;}
    }
}

After this, I build the project to get the assembly.

dotnet build /p:Platform=anycpu

The template file I created uses the class from the referenced assembly:

<#
var helper = new Example.Helper
{
    FuncProperty = null
};
#>

When I try to run the template with the command:

t4 Example.tt --out=Example.Generated.cs -P=<absolute-path-prefix>\Example\bin\Debug\net7.0 -r=System.Xml.dll -r=Example.dll --debug --verbose

I got the error saying that my property does not exist.

ERROR: Error running transform: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
 ---> System.MissingMethodException: Method not found: 'Void Example.Helper.set_FuncProperty(System.Func`2<System.Uri,System.Xml.XmlReader>)'.
   at Microsoft.VisualStudio.TextTemplating2534841a.GeneratedTextTransformation.TransformText()
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   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.MethodBase.Invoke(Object obj, Object[] parameters)
   at Mono.TextTemplating.CompiledTemplate.TemplateProcessor.CreateAndProcess(ITextTemplatingEngineHost host, CompiledAssemblyData templateAssemblyData, String templateAssemblyFile, String fullName, CultureInfo culture, String[] referencedAssemblyFiles)

Can you explain why the T4 tool says the property is not found in the class?
It looks like the generated text transformation code compiles but does not run.