Following #17519, we should see if it is possible for the F# compiler to emit a call to the System.Diagnostics.Debug.Assert overload that takes a message defaulting to CallerArgumentExpression for all usages of the assert keyword.

I.e., an expression like this

assert not true

would be translated to

System.Diagnostics.Debug.Assert (not true, "not true")

Likewise:

assert (x = 3)

→

System.Diagnostics.Debug.Assert ((x = 3), "(x = 3)")

etc.

The C# compiler now does this for System.Diagnostics.Debug.Assert(booleanExpr) by means of the OverloadResolutionPriorityAttribute, which F# does not currently support: #16967 (comment)

dotnet/csharplang#7906: developers can add weight to which methods are better in overload resolution. This seems unlikely to impact F# as much.

Want to point out one place this will intersect with F#. Consider that very likely Debug will end up looking like the following:

public static class Debug
{
  [OverloadResolutionPriority(-1)]
  public static void Assert(bool condition) { ... } 

  public static void Assert(bool condition, [CallerArgumentExpression] string? message = "") { ... }
}

Nothing will break for F# here when this happens, code will still compile as it used to. The experience for C# though will improve from a lot of Debug.Assert failed messages to the actual expression that passed into the assert. This is one part I thought might be interesting to F# .

See the BCL source:

[Conditional("DEBUG")]
[OverloadResolutionPriority(-1)] // lower priority than (bool, string) overload so that the compiler prefers using CallerArgumentExpression
public static void Assert([DoesNotReturnIf(false)] bool condition) =>
    Assert(condition, string.Empty, string.Empty);


[Conditional("DEBUG")]
public static void Assert([DoesNotReturnIf(false)] bool condition, [CallerArgumentExpression(nameof(condition))] string? message = null) =>
    Assert(condition, message, string.Empty);

SharpLab F#
SharpLab C#

We could in theory do this in the F# compiler specifically for the assert keyword, without needing to support OverloadResolutionPriorityAttribute in general, by emitting a call to the new overload when it is available here: