Re: [PATCH] gnu: libffi: Add unreleased patch to fix float128 on powerpc64le.

[Mark H Weaver <mhw@netris.org>]

Earlier, I wrote:
> When invoking 'patch' in Guix, you should *always* use "--force" instead
> of "--batch".

(See <https://bugs.gnu.org/45252#19> for my earlier message).

Since writing the message above, I've found another problem in the same
commit (7eaa2f24ea77cddbb4bbc2d6a6905673a36f8f99): it searches for the
'patch' program in 'inputs'.  This is a mistake, because when
cross-compiling, 'inputs' will contain software compiled to run on the
target system instead of the build system.

If 'native-inputs' is not #f, we should search for the 'patch' program
in 'native-inputs' instead of 'inputs'.  Unless there's now a better way
that I don't know, I suggest adding 'native-inputs' to the list of
keyword arguments accepted by the 'lambda*', and changing 'inputs' to
"(or native-inputs inputs)" in the call to 'assoc-ref'.  Something like
this (untested):

_ ,@(if (string-prefix? "powerpc64le-" (or (%current-target-system)
__________________________________________ (%current-system)))
_______ '(#:phases (modify-phases %standard-phases
____________________ (add-after 'unpack 'apply-patch2
______________________ (lambda* (#:key inputs native-inputs
________________________________ #:allow-other-keys)
________________________ (let ((patch (assoc-ref (or native-inputs inputs)
________________________________________________ "powerpc64le-patch")))
__________________________ (invoke "patch" "--force" "-p1"
__________________________________ "-i" patch))))))
_______ '())

I see now that both of these mistakes were already present in the
"powerpc-*" case immediately above the recently-added "powerpc64le-*"
case.  The "powerpc-*" case was added earlier this year in the following
commit:

  https://git.sv.gnu.org/cgit/guix.git/commit/?id=02f5ee01c96589fc13f1e21b85b0b48100aec4e8

I'm CC'ing 'guix-devel' to raise awareness about these common mistakes,
in the hopes that reviewers will be more likely to notice them in the
future.

      Thanks,
        Mark