Changing F# literals is not propagated properly to dependent projects in incremental builds

[luithefirst]

I have a F# class library with a literal in it and a C# console application that uses it. When the literal is changed, the F# library is rebuilt, but not the C# project, resulting in printing the wrong value. Also, if the C# project is changed and "rebuilt" (incremental), the old literal is used. Only if you make a clean rebuild, the proper literal value is used.

The F# library:

namespace ClassLibrary

module Literals = 
    [<Literal>]
    let Number = 2048

C# app:

Console.WriteLine($"The number is {ClassLibrary.Literals.Number}");

1. The output of a clean rebuild is 2048.
2. When the literal is changed to something else, the output is still 2048.
3. When the C# project is changed to e.g. print ClassLibrary.Literals.Number + 1, it will print 2049 as if the literal still was 2048.

You need to manually trigger a rebuild (RMB -> Rebuild in VS) or clean the solution to resolve the inconsistency.

I'm using VS 17.14.8 with the .NET 8.0.411 SDK.

You can also clone this repository to reproduce the issue:
https://github.com/luithefirst/FSharpLiteral

[T-Gro]

The reason likely is:

C# spec, section 14.6.1 ("Constant declarations"):

"The value of a constant is obtained at compile-time and not at run-time. If a constant is imported from another assembly, its value is copied into the referencing assembly at compile-time."

I will check how best the F# compiler can communicate this change which is relevant for source-code invalidation (even though the F# lib was binary usable the same way)

[luithefirst]

Thanks!