I have a .NET 8 app which uses a custom conditional compilation symbol as follows:

#if MY_SYMBOL
    public MyConstructor() : base(ArgumentOne) { }
#else
    public MyConstructor() : base(ArgumentTwo) 
    {
        throw new Exception("A compilation-time tier symbol must be set");
    }
#endif

I am finding that if I pass my symbol to the dotnet run command as the DefineConstants property like this – dotnet run -p:DefineConstants=MY_SYMBOL – then it works fine (code is compiled with the first constructor).

However, if I do this in my csproj file like this…

  <PropertyGroup>
    <DefineConstants>$(DefineConstants);MY_SYMBOL</DefineConstants>
  </PropertyGroup>

…then run the app in debug mode using a launch profile, the symbol isn’t set so the code is compiled with the second constructor above.

What is the reason for this? I’m trying to achieve a scenario where I have a default symbol in my local dev environment, then pass a custom symbol via dotnet run in my Dockerfile for deploy environments. Is there a better, more reliable approach?