Hi,

As bug#60200 [1], the issue is one that many of us often hit: packages
with several versions and when the highest one is not the default.

Other said, build systems use some version for compiler and tools but
Guix can also offer more recent versions for these very same compilers
and tools.  It leads to the issue when selecting the name of a compiler
or tool (command line or manifest).  The user does not get the ones used
as default by build system.

In addition to [1], another example:

--8<---------------cut here---------------start------------->8---
$ guix shell ocaml ocaml-ppxlib -- ocaml --version
The OCaml toplevel, version 5.0.0
--8<---------------cut here---------------end--------------->8---

But the OCaml libraries are built using OCaml compiler v4.14, thus it
leads to error as:

--8<---------------cut here---------------start------------->8---
Error: /gnu/store/vglxlc8riynj1g937clvwv8yg40lln6z-profile/lib/ocaml/site-lib/ppxlib/ppxlib.cmi
       is not a compiled interface for this version of OCaml.
It seems to be for an older version of OCaml.
--8<---------------cut here---------------end--------------->8---

For other cases, such issue is avoided by appending the suffix -next to
package name; as with ghc-next, python-numpy-next, emacs-next, etc.

Personally, I find the -next trick useful because the package name
reflects that it is not the default.  However, it can be annoying to
update manifest files when this -next is becoming default.

Well, what do people think about this Lars’s patch?