Add System.Runtime.CompilerServices.RuntimeFeature.PortablePdb

[tmat]

Currently there is no support for Portable PDBs in Desktop FX. We are finishing support in stack traces for portable and embedded PDBs for 4.7.1. Features that generate code at runtime (such as scripting) would benefit from being able to detect whether the runtime supports Portable PDBs or not, as they could emit Portable PDBs instead of Windows PDBs. Emitting Portable PDBs has perf benefits.

In order to make the feature detection consistent across all platforms we propose to add the following APIs to netstandard as well.

Proposed API

namespace System.Runtime.CompilerServices
{
    public static class RuntimeFeature
    {
        public const string PortablePdb = nameof(PortablePdb);

        // returns true for feature == "PortablePdb"
        public static bool IsSupported(string feature);
    }
}

// Usage

if (RuntimeFeature.IsSupported("PortablePdb")
{
      // Emit code with Portable debug info
}

[tmat]

@karelz What's the process for approving this API for Desktop FX 4.7.1?

[tmat]

/cc @noahfalk

[karelz]

@tmat email fxdc. @leecow might also help.

[tmat]

@marek-safar What's the process of adding APIs to Mono? If we added this API to 4.7.1 should it also be added to Mono at the same time or earlier? Do you have a release synchronized with Desktop FX?

[karelz]

BTW: Mono is trying to reuse CoreFX source libraries, so it will be likely in the same boat as .NET Core.

[weshaggard]

In order to make the feature detection consistent across all platforms we propose to add the following APIs to netstandard as well.

The RuntimeFeature API isn't slated for netstandard yet, at least not netstandard2.0. It would be good to get it into .NET Framework 4.7.1 however.

[marek-safar]

@tmat it's enough to cc me on the commit where the change is being worked on for CoreFX or CoreRT. We can add it earlier if the API is approved.

[terrajobst]

Looks good as proposed

[jcouv]

@tmat I see that the RuntimeFeatures "PortablePdb" flag was added. Are we using it in Roslyn at this point?
If we do, I'll use that as an example for a contributor who is working on another feature that needs a flag.

[tmat]

@jcouv We are not using it yet.