Source generator fails when arguments classes are named the same but belong to different namespaces

[atifaziz]

If two arguments classes in the same project are named identically but belong in different namespace:

using DocoptNet;

namespace Namespace1
{
    [DocoptArguments]
    sealed partial class ProgramArguments
    {
        const string Help = "Usage: program";
    }
}

namespace Namespace2
{
    [DocoptArguments]
    sealed partial class ProgramArguments
    {
        const string Help = "Usage: program";
    }
}

then build fails with the following error indicating that the source generator failed:

error CS8785: Generator 'SourceGenerator' failed to generate source. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'ArgumentException' with message 'The hintName 'ProgramArguments.cs' of the added source file must be unique within a generator.