guix: gexp: Define gexp->approximate-sexp.

It will be used in the 'optional-tests' linter.

* guix/gexp.scm (gexp->approximate-sexp): New procedure.
* tests/gexp.scm
  ("no references", "unquoted gexp", "unquoted gexp (native)")
  ("spliced gexp", "unspliced gexp, approximated")
  ("unquoted gexp, approximated"): Test it.
* doc/gexp.scm ("G-Expressions"): Document it.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index e0668b1f5f..e39e4eb7be 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -10046,6 +10046,16 @@ corresponding to @var{obj} for @var{system}, cross-compiling for
 has an associated gexp compiler, such as a @code{<package>}.
 @end deffn
 
+@deffn {Procedure} gexp->approximate-sexp @var{gexp}
+Sometimes, it may be useful to convert a G-exp into a S-exp.  For
+example, some linters (@pxref{Invoking guix lint}) peek into the build
+phases of a package to detect potential problems.  This conversion can
+be achieved with this procedure.  However, some information can be lost
+in the process.  More specifically, lowerable objects will be silently
+replaced with some arbitrary object -- currently the list
+@code{(*approximate*)}, but this may change.
+@end deffn
+
 @node Invoking guix repl
 @section Invoking @command{guix repl}