UserFacing printer forgets minus sign for decimals in (-1, 0)

[Pierre GOUTAGNY]

While trying to print Runtime.decimals I think I've found a bug in the user-facing printer.

Here is a code example (in OCaml) demonstrating the behaviour :

open Catala_utils
open Shared_ast

let print_decimals () =
  let decimals = [1.; 0.5; 0.; -0.; -0.5; -1.] in
  let m = Untyped {pos = Pos.no_pos} in
  Message.emit_result "float\tQ\texpr\texpr db\tuserfacing";
  List.iter
    (fun f ->
      let q = Q.of_float f in
      let e = Expr.unbox (Expr.elit (LRat q) m) in
      Message.emit_result "%s\t%s\t%a\t%a\t%a"
      (string_of_float f)
      (Q.to_string q)
      (Print.expr ~debug:false ()) e
      (Print.expr ~debug:true ()) e
      (Print.UserFacing.value En) e
    )
    decimals;;

print_decimals ()

And the printed result:

[RESULT] float	Q	expr	expr db	userfacing
[RESULT] 1.	1	1.	1.	1.0
[RESULT] 0.5	1/2	0.5	0.5	0.5
[RESULT] 0.	0	0.	0.	0.0
[RESULT] -0.	0	0.	0.	0.0
[RESULT] -0.5	-1/2	-0.5	-0.5	0.5
[RESULT] -1.	-1	-1.	-1.	-1.0

As you can see, -0.5 is missing its leading minus sign when using the user-facing printer. I only saw this happen for decimals between -1 and 0, so it may have to do with the fact that those numbers have an integer part of "-0" which is printed as "0".