Instantiating an exception with wrong payload compiles and fails at run-time

[hvester]

It is possible to instantiate a user defined exception by giving an interpolated string (without anything interpolated) as a constructor argument without compile-time error although the constructor expects something else.

Note that the problem does not reproduce (i.e. compile error is given as expected) if normal string is used instead of interpolated string or something is interpolated in the interpolated string.

Repro steps

1. Create new console application
2. Add the code below to Program.fs
3. Run dotnet run

type Foo = { Bar: int }

exception MyException of string * Foo

try
    raise (MyException($"BOOM"))
    // raise (MyException("BOOM")) // <- Compile-time error
    // raise (MyException($"BOOM {42}")) // <- Compile-time error
with
| MyException(msg, foo) ->
    printfn "%A" foo

Expected behavior

Code should not compile.

Actual behavior

Code compiles, but fails at run-time with following error:

Fatal error. System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
   at System.Runtime.CompilerServices.CastHelpers.ChkCastAny(Void*, System.Object)
   at Microsoft.FSharp.Core.LanguagePrimitives+IntrinsicFunctions.UnboxGeneric[[System.__Canon, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.Object)
   at Microsoft.FSharp.Core.PrintfImpl+GenericToString@969-3[[System.__Canon, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Invoke(System.Object)
   at Microsoft.FSharp.Core.PrintfImpl+OneStepWithArg@501-1[[System.__Canon, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.__Canon, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.__Canon, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.__Canon, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Invoke(System.__Canon)
   at <StartupCode$ExceptionErrorReproduction>.$Program.main@()

Related information

• Operating system: macOS 12.3.1
• .NET SDK version: 6.0.302

[vzarytovskii]

Yeah, we should fix it

[vzarytovskii]

This is even easier to repro underlying issue:

let foo:int = $"a"

will result in the following codegen for foo

IL_0000: ldstr ""
IL_0005: ret

however foo is int32

.method public specialname static int32 get_foo