Scheme parameters names lost with Lilypond 2.23.8

[Stéphane SOPPERA]

Hi,

While trying to make sure my automatic documentation generation code 
works with Lilypond 2.23.8 (and especially Guile 2.2) I noticed a bug 
that may be due to how Lilypond is using Guile 2.2.

The current version of my code uses /(p//rocedure-source)/ 
<https://github.com/soppera/lilypond-harmony-rules/blob/master/generate-doc.scm#L45> 
to get the names of the parameters of my functions & methods and 
generate the documentation.
I noticed that with Guile 2.2 I always get /#f/ when I call 
/(//procedure-source)/. But we now have /(program-lambda-list)/ 
<https://www.gnu.org/software/guile/manual/html_node/Compiled-Procedures.html> 
that removes the need from parsing the source to get the parameter names.

Thus I tried to use /(program-lambda-list)/ to get the parameters names 
with Lilypond 2.23.8 (i.e. Guile 2.2) but this fails and instead I get 
anonymized parameters ("a", "b"... instead of the expected values).

To illustrate the issue let's first see what happens with Lilypond 2.22 
(and thus Guile 1.8), compiling:

\version "2.22.0"

#(begin
  (define (f lhs rhs) (+ lhs rhs))

  (display "\nUsing Guile ")
  (display (version))
  (newline)

  (display "source: ")
  (display (procedure-source f))
  (newline))

prints:

GNU LilyPond 2.22.2
Processing `test_2.22.ly'
Parsing...
Using Guile 1.8.7
source: (lambda (lhs rhs) (+ lhs rhs))

(we can't use /(program-lambda-list)/ here since it is not supported by 
Guile 1.8)

With Lilypond 2.23 (and thus Guile 2.2), compiling:

\version "2.23.8"

#(begin
  (use-modules (system vm program))
  (define (f lhs rhs) (+ lhs rhs))

  (display "Using Guile ")
  (display (version))
  (newline)

  (display "λ-list: ")
  (display (program-lambda-list f))
  (newline)

  (display "source: ")
  (display (procedure-source f))
  (newline))

prints:

GNU LilyPond 2.23.8 (running Guile 2.2)
Processing `test_2.23.ly'
Parsing...Using Guile 2.2.7
λ-list: *(a b)*
source: *#f*

We can see that:

1. We don't have access to the function source anymore (as when using
   Guile 2.2 directly).
2. /(program-lambda-list)/ returns "(a b)" instead of "(lhs rhs)",
   erasing the parameters' names.

To confirm if this is the default behavior of Guile 2.2, I tested this 
Guile script:

(use-modules (system vm program))
(define (f lhs rhs) (+ lhs rhs))

(display "Using Guile ")
(display (version))
(newline)

(display "λ-list: ")
(display (program-lambda-list f))
(newline)

(display "source: ")
(display (procedure-source f))
(newline)

Running Guile command line tool on this script with the default 
parameters result in:

Using Guile 2.2.7
λ-list: (lhs rhs)
source: #f

We can see that:

1. Guile 2.2 does not return the source either.
2. Guile 2.2 does return "(lhs rhs)" as expected,  and not "(a b)" as
   Lilypond 2.23.8 is doing.

I dig a bit further into this issue and I can make Guile 2.2 behave like 
Lilypond by using the flags:

 * --fresh-auto-compile
 * --no-auto-compile

*With those two flags *I indeed get the same output as with Lilypond 2.23.8:

Using Guile 2.2.7
λ-list: (a b)
source: #f

Note that using --fresh-auto-compile is _mandatory_ since without it 
Guile seems to use previous auto-compilation's output and indeed prints 
the correct list of parameters.


To summarize the issues:

 * Lilypond 2.23.8 is using Guile 2.2 which does not support
   /(//proceduce-source)/ anymore.
 * But Guile 2.2 offers /(program-lambda-list)/ which can replace the
   use of /(//proceduce-source)/ to get the parameters' names.
 * The issue is that the way Lilypond 2.23.8 uses Guile 2.2 erases the
   parameter names returned by /(program-lambda-list)/, making it
   impossible to use this method either.

Please let me know if you need more details.