Parameterless constructors removed on publish if Trim Unused Code is selected?

[amorenojr]

Trim Unused Code Bug

Description

When publishing in Visual Studio, the option to Trim Unused Code is available to select in the publishing profile settings. This feature is VERY useful when much of the code in the application is not used and it is why I usually have it checked by default. However, I recently came across an issue where I published an application to a folder where I used both the Produce a single file and Trim Unused Code options but when I ran the application an exception was thrown that said, "Namespace.Class cannot be serialized because it does not have a parameterless constructor." I am familiar with this exception because I have seen it before. It is the result of using the native .NET serializer and deserializer which require the parameterless constructor in the class.

After triple checking that the class in question had the parameterless constructor and republishing with newly created publishing profiles but I was still getting the same exception.

I went looking for other issues but remembered that all was working in .NET 6 and the purpose of this project was to upgrade the application from .NET 6 to .NET 8.

So out of a gut feeling, I unchecked the Trim Unused Code because I logically arrived at the idea that the parameterless constructor was "unused" in the application as it is written. I assume since I am not explicitly calling the parameterless constructor in application, the compiler sees it as "unused" and therefore trims it out?

Anyway, if my suspicision are correct, this SHOULD NOT HAPPEN! Please fix! Else, what can I do to use the Trim Unused Code option when publishing.

To Reproduce

See attached ExampleApp.zip file with VS solution.
Publish each profile
Use a terminal (I used Powershell) and run each published EXE to see the difference

Exception on the wTrimUnusedCode only.

ExampleNamespace.ExampleClass cannot be serialized because it does not have a parameterless constructor.   at System.Xml.Serialization.TypeDesc.CheckSupported()
   at System.Xml.Serialization.TypeScope.GetTypeDesc(Type, MemberInfo, Boolean, Boolean)
   at System.Xml.Serialization.TypeScope.GetTypeDesc(Type, MemberInfo, Boolean)
   at System.Xml.Serialization.ModelScope.GetTypeModel(Type, Boolean)
   at System.Xml.Serialization.ModelScope.GetTypeModel(Type)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(Type, XmlRootAttribute , String )
   at System.Xml.Serialization.XmlSerializer..ctor(Type type, String defaultNamespace)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type)
   at System.Xml.Serialization.XmlUtils.Deserialize[T](FileInfo) in %USERPROFILE%\source\repos\ExampleApp\ExampleApp\XmlUtils.cs:line 22

Further technical details

• Output of dotnet --info

  .NET SDK:
      Version:           9.0.101
      Commit:            eedb237549
      Workload version:  9.0.100-manifests.4a280210
      MSBuild version:   17.12.12+1cce77968
  
      Runtime Environment:
      OS Name:     Windows
      OS Version:  10.0.19045
      OS Platform: Windows
      RID:         win-x64
      Base Path:   C:\Program Files\dotnet\sdk\9.0.101\
  
      .NET workloads installed:
      [aspire]
      Installation Source: VS 17.12.35527.113
      Manifest Version:    8.2.2/8.0.100
      Manifest Path:       C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.aspire\8.2.2\WorkloadManifest.json
      Install Type:              Msi
  
      Configured to use loose manifests when installing new manifests.
  
      Host:
      Version:      9.0.0
      Architecture: x64
      Commit:       9d5a6a9aa4
  
      .NET SDKs installed:
      6.0.203 [C:\Program Files\dotnet\sdk]
      6.0.428 [C:\Program Files\dotnet\sdk]
      9.0.101 [C:\Program Files\dotnet\sdk]
  
      .NET runtimes installed:
      Microsoft.AspNetCore.App 6.0.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
      Microsoft.AspNetCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
      Microsoft.AspNetCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
      Microsoft.AspNetCore.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
      Microsoft.AspNetCore.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
      Microsoft.NETCore.App 6.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
      Microsoft.NETCore.App 6.0.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
      Microsoft.NETCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
      Microsoft.NETCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
      Microsoft.NETCore.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
      Microsoft.NETCore.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
      Microsoft.WindowsDesktop.App 6.0.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
      Microsoft.WindowsDesktop.App 6.0.15 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
      Microsoft.WindowsDesktop.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
      Microsoft.WindowsDesktop.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
      Microsoft.WindowsDesktop.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
      Microsoft.WindowsDesktop.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  
      Other architectures found:
      x86   [C:\Program Files (x86)\dotnet]
          registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]
  
      Environment variables:
      Not set
  
      global.json file:
      Not found
  
      Learn more:
      https://aka.ms/dotnet/info
  
      Download .NET:
      https://aka.ms/dotnet/download
  

• The IDE info

  Microsoft Visual Studio Professional 2022
  Version 17.12.3
  VisualStudio.17.Release/17.12.3+35527.113
  Microsoft .NET Framework
  Version 4.8.09037