It looks like runtime verifies variance safety for static members in interfaces and throws System.TypeLoadException #39612
Description
Below is IL equivalent to the following C# code:
class Program
{
static void Main()
{
System.Console.WriteLine(I2<string, string>.M1("a"));
System.Console.WriteLine(I2<string, string>.M2("b"));
}
}
interface I2<out T1, in T2>
{
static T1 M1(T1 x) => x;
static T2 M2(T2 x) => x;
}The IL:
// Microsoft (R) .NET Framework IL Disassembler. Version 4.8.3928.0
// Copyright (c) Microsoft Corporation. All rights reserved.
// Metadata version: v4.0.30319
.assembly extern System.Runtime
{
.publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A ) // .?_....:
.ver 4:2:2:0
}
.assembly extern System.Console
{
.publickeytoken = (B0 3F 5F 7F 11 D5 0A 3A ) // .?_....:
.ver 4:1:2:0
}
.assembly ConsoleApp5
{
.custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilationRelaxationsAttribute::.ctor(int32) = ( 01 00 08 00 00 00 00 00 )
.custom instance void [System.Runtime]System.Runtime.CompilerServices.RuntimeCompatibilityAttribute::.ctor() = ( 01 00 01 00 54 02 16 57 72 61 70 4E 6F 6E 45 78 // ....T..WrapNonEx
63 65 70 74 69 6F 6E 54 68 72 6F 77 73 01 ) // ceptionThrows.
// --- The following custom attribute is added automatically, do not uncomment -------
// .custom instance void [System.Runtime]System.Diagnostics.DebuggableAttribute::.ctor(valuetype [System.Runtime]System.Diagnostics.DebuggableAttribute/DebuggingModes) = ( 01 00 07 01 00 00 00 00 )
.custom instance void [System.Runtime]System.Runtime.Versioning.TargetFrameworkAttribute::.ctor(string) = ( 01 00 18 2E 4E 45 54 43 6F 72 65 41 70 70 2C 56 // ....NETCoreApp,V
65 72 73 69 6F 6E 3D 76 33 2E 31 01 00 54 0E 14 // ersion=v3.1..T..
46 72 61 6D 65 77 6F 72 6B 44 69 73 70 6C 61 79 // FrameworkDisplay
4E 61 6D 65 00 ) // Name.
.custom instance void [System.Runtime]System.Reflection.AssemblyCompanyAttribute::.ctor(string) = ( 01 00 0B 43 6F 6E 73 6F 6C 65 41 70 70 35 00 00 ) // ...ConsoleApp5..
.custom instance void [System.Runtime]System.Reflection.AssemblyConfigurationAttribute::.ctor(string) = ( 01 00 05 44 65 62 75 67 00 00 ) // ...Debug..
.custom instance void [System.Runtime]System.Reflection.AssemblyFileVersionAttribute::.ctor(string) = ( 01 00 07 31 2E 30 2E 30 2E 30 00 00 ) // ...1.0.0.0..
.custom instance void [System.Runtime]System.Reflection.AssemblyInformationalVersionAttribute::.ctor(string) = ( 01 00 05 31 2E 30 2E 30 00 00 ) // ...1.0.0..
.custom instance void [System.Runtime]System.Reflection.AssemblyProductAttribute::.ctor(string) = ( 01 00 0B 43 6F 6E 73 6F 6C 65 41 70 70 35 00 00 ) // ...ConsoleApp5..
.custom instance void [System.Runtime]System.Reflection.AssemblyTitleAttribute::.ctor(string) = ( 01 00 0B 43 6F 6E 73 6F 6C 65 41 70 70 35 00 00 ) // ...ConsoleApp5..
.hash algorithm 0x00008004
.ver 1:0:0:0
}
.module ConsoleApp5.dll
// MVID: {580B623A-FB1A-403C-8F9C-8DB0E42D429C}
.imagebase 0x00400000
.file alignment 0x00000200
.stackreserve 0x00100000
.subsystem 0x0003 // WINDOWS_CUI
.corflags 0x00000001 // ILONLY
// Image base: 0x047E0000
// =============== CLASS MEMBERS DECLARATION ===================
.class private auto ansi beforefieldinit Program
extends [System.Runtime]System.Object
{
.method private hidebysig static void Main() cil managed
{
.entrypoint
// Code size 34 (0x22)
.maxstack 8
IL_0000: nop
IL_0001: ldstr "a"
IL_0006: call !0 class I2`2<string,string>::M1(!0)
IL_000b: call void [System.Console]System.Console::WriteLine(string)
IL_0010: nop
IL_0011: ldstr "b"
IL_0016: call !1 class I2`2<string,string>::M2(!1)
IL_001b: call void [System.Console]System.Console::WriteLine(string)
IL_0020: nop
IL_0021: ret
} // end of method Program::Main
.method public hidebysig specialname rtspecialname
instance void .ctor() cil managed
{
// Code size 8 (0x8)
.maxstack 8
IL_0000: ldarg.0
IL_0001: call instance void [System.Runtime]System.Object::.ctor()
IL_0006: nop
IL_0007: ret
} // end of method Program::.ctor
} // end of class Program
.class interface private abstract auto ansi I2`2<+ T1,- T2>
{
.method public hidebysig static !T1 M1(!T1 x) cil managed
{
// Code size 2 (0x2)
.maxstack 8
IL_0000: ldarg.0
IL_0001: ret
} // end of method I2`2::M1
.method public hidebysig static !T2 M2(!T2 x) cil managed
{
// Code size 2 (0x2)
.maxstack 8
IL_0000: ldarg.0
IL_0001: ret
} // end of method I2`2::M2
} // end of class I2`2
// =============================================================
// *********** DISASSEMBLY COMPLETE ***********************
An attempt to run it produces the following output:
Unhandled exception. System.TypeLoadException: Could not load type 'I2`2' from assembly 'ConsoleApp5, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'
because a covariant or contravariant type parameter was used illegally in the signature for an argument in method 'M1'.
at Program.Main()
Expected output:
a
b
This is blocking implementation of the following C# feature: https://github.com/dotnet/csharplang/blob/master/proposals/variance-safety-for-static-interface-members.md