Mark Assembly.CodeBase as obsolete

[terrajobst]

Assembly.Location and Assembly.CodeBase are very similar, but not the same thing. To reduce confusion, we should mark it as obsolete.

Reason

Having two things that are similar, but not identical always causes confusion. Here is an example.

As @jkotas said:

Assembly.Location is strictly better than Assembly.CodeBase.

Assembly.CodeBase is an obsolete property. The only reason why it was included in .NET Core was .NET Framework compatibility. The original purpose of Assembly.CodeBase was CAS (Code Access Security). It was meant to describe where the assembly was downloaded from for the Internet Zone security checks. It also explains some of its weird behaviors. For example, if the assembly is loaded as byte array, it returns the location of the caller of the Assembly.Load method.

Proposed API

namespace System.Reflection
{
    public partial class Assembly
    {
        [Obsolete("Use Location instead.")]
        public virtual string CodeBase { get; }
    }
}

[terrajobst]

Video

Looks good. We should also mark it as [EditorBrowsable(Never)].

namespace System.Reflection
{
    public partial class Assembly
    {
        [Obsolete("Use Location instead.")]
        public virtual string CodeBase { get; }
    }
}

[vitek-karas]

Should we also consider obsoleting AssemblyName.CodeBase? It's not exactly the same thing, but quite related - in fact that property has no functional effect (trying to load assembly via AssemblyName will ignore the CodeBase property anyway: https://github.com/dotnet/coreclr/blob/master/src/System.Private.CoreLib/src/System/Reflection/Assembly.CoreCLR.cs#L63

[jkotas]

Assembly.EscapedCodeBase should be marked as obsolete as well.

[bitbonk]

Just out of curiosity: Since those APIs are part of .NET Standard, what implications does marking APIs as obsolete have for .NET Standard?

Since in .NET Standard, APIs cannot be removed, only added, does that mean you will only obsolete those APs but never remove them? Or will .NET Standard itself become obsolete due to the unification in .NET 5.

[jkotas]

Right, we do not have plans to remove any netstandard APIs.