VS 15.5 Preview: VerificationException in otherwise valid function

[yaakov-h]

Version Used:
Microsoft Visual Studio Enterprise 2017 Preview
Version 15.5.0 Preview 1.0

Steps to Reproduce:

1. Create a .NET Framework Console Application
2. Replace the contents of Program.cs with the code below.
3. Run the program.

Expected Behavior:

The program prints "Comparison: 0"

Actual Behavior:

The program crashes with a VerificationException in StructyMcStructFace.CompareTo.

Code:

using System;
using System.Security;

[assembly: AllowPartiallyTrustedCallers()]

namespace RoslynRepro155
{
	class Program
	{
		static void Main(string[] args)
		{
			var color1 = new StructyMcStructFace(TColorType.Automatic);
			var color2 = new StructyMcStructFace(TColorType.Automatic);

			var result = color1.CompareTo(color2);
			Console.WriteLine("Comparison: {0}", result);
			Console.ReadKey();
		}
	}

	public enum TAutomaticColor
	{
	}

	public enum TColorType
	{
		Automatic,
		RGB,
		Theme,
		Indexed
	}

	public struct StructyMcStructFace
	{
		public StructyMcStructFace(TColorType type)
		{
			ColorType = type;
			automaticType = default(TAutomaticColor);

		}

		readonly TAutomaticColor automaticType;

		public TColorType ColorType { get; }

		public int CompareTo(StructyMcStructFace other)
		{
			switch (ColorType)
			{
				case TColorType.Automatic:
					return automaticType.CompareTo(other.automaticType);
			}

			return 0;
		}
	}
}

IL of CompareTo with Visual Studio 2017 v15.4.0:

.method public hidebysig 
	instance int32 CompareTo (
		valuetype RoslynRepro155.StructyMcStructFace other
	) cil managed 
{
	// Method begins at RVA 0x20b0
	// Code size 53 (0x35)
	.maxstack 2
	.locals init (
		[0] valuetype RoslynRepro155.TColorType,
		[1] valuetype RoslynRepro155.TAutomaticColor,
		[2] int32
	)

	IL_0000: nop
	IL_0001: ldarg.0
	IL_0002: call instance valuetype RoslynRepro155.TColorType RoslynRepro155.StructyMcStructFace::get_ColorType()
	IL_0007: stloc.0
	IL_0008: ldloc.0
	IL_0009: brfalse.s IL_000d

	IL_000b: br.s IL_002f

	IL_000d: ldarg.0
	IL_000e: ldfld valuetype RoslynRepro155.TAutomaticColor RoslynRepro155.StructyMcStructFace::automaticType
	IL_0013: stloc.1
	IL_0014: ldloca.s 1
	IL_0016: ldarg.1
	IL_0017: ldfld valuetype RoslynRepro155.TAutomaticColor RoslynRepro155.StructyMcStructFace::automaticType
	IL_001c: box RoslynRepro155.TAutomaticColor
	IL_0021: constrained. RoslynRepro155.TAutomaticColor
	IL_0027: callvirt instance int32 [mscorlib]System.Enum::CompareTo(object)
	IL_002c: stloc.2
	IL_002d: br.s IL_0033

	IL_002f: ldc.i4.0
	IL_0030: stloc.2
	IL_0031: br.s IL_0033

	IL_0033: ldloc.2
	IL_0034: ret
} // end of method StructyMcStructFace::CompareTo

IL of CompareTo with Visual Studio 2017 v15.5.0 Preview:

.method public hidebysig 
	instance int32 CompareTo (
		valuetype RoslynRepro155.StructyMcStructFace other
	) cil managed 
{
	// Method begins at RVA 0x20b0
	// Code size 50 (0x32)
	.maxstack 2
	.locals init (
		[0] valuetype RoslynRepro155.TColorType,
		[1] int32
	)

	IL_0000: nop
	IL_0001: ldarg.0
	IL_0002: call instance valuetype RoslynRepro155.TColorType RoslynRepro155.StructyMcStructFace::get_ColorType()
	IL_0007: stloc.0
	IL_0008: ldloc.0
	IL_0009: brfalse.s IL_000d

	IL_000b: br.s IL_002c

	IL_000d: ldarg.0
	IL_000e: ldflda valuetype RoslynRepro155.TAutomaticColor RoslynRepro155.StructyMcStructFace::automaticType
	IL_0013: ldarg.1
	IL_0014: ldfld valuetype RoslynRepro155.TAutomaticColor RoslynRepro155.StructyMcStructFace::automaticType
	IL_0019: box RoslynRepro155.TAutomaticColor
	IL_001e: constrained. RoslynRepro155.TAutomaticColor
	IL_0024: callvirt instance int32 [mscorlib]System.Enum::CompareTo(object)
	IL_0029: stloc.1
	IL_002a: br.s IL_0030

	IL_002c: ldc.i4.0
	IL_002d: stloc.1
	IL_002e: br.s IL_0030

	IL_0030: ldloc.1
	IL_0031: ret
} // end of method StructyMcStructFace::CompareTo

[jcouv]

Tagging @gafter @TyOverby

[svick]

This seems to be similar to #22485, except here it's not just PEVerify complaining, it's also the runtime, due to the presence of AllowPartiallyTrustedCallers. And the workaround mentioned there does work: adding <Features>peverify-compat</Features> to csproj makes the code work for me in VS 15.5 Preview 1.

[jcouv]

Tagging @VSadov. We should probably update the breaking changes doc and give a one-liner there (relates to #21269).

[VSadov]

We could also check for things like AllowPartiallyTrustedCallers or security transparent and disable the optimizations that go beyond verification rules on desktop.

[VSadov]

logged #22712

At least for APTCA, it seems possible and reasonable to sniff for the attribute and enable compat mode automatically. Same might be true for SecurityTransparent

[jcouv]

@VSadov Good to close?

[VSadov]

Yes. we have short term a solution that we believe is the right balance between desire to use new features and produce code compatible with old verification rules: #22772

We are also working on extending verification rules:
dotnet/designs#17
dotnet/designs#21