Rewriting inputs and ’arguments’ after patch #43578

[zimoun]

Dear,

Let consider the package ’emacs-magit’.  It does not depend on
’emacs-minimal’ but instead the argument is replaced by ’emacs-no-x’,
see: 

--8<---------------cut here---------------start------------->8---
      (build-system emacs-build-system)
      (arguments
       `(#:emacs ,emacs-no-x            ;module support is required
         #:tests? #t
--8<---------------cut here---------------end--------------->8---

which is for example confirmed by “guix graph –path”:

--8<---------------cut here---------------start------------->8---
$ guix graph --path emacs-magit emacs-minimal
guix graph: error: no path from 'emacs-magit@2.90.1-6.7f486d4' to 
'emacs-minimal@27.1'

$ guix graph --path emacs-magit emacs-no-x
emacs-magit@2.90.1-6.7f486d4
emacs-libgit@20200515-1.0ef8b13
emacs-no-x@27.1
--8<---------------cut here---------------end--------------->8---


Therefore, it is not possible to rewrite this “inputs“ (using the patch
[1]), as the dry-run shows:

--8<---------------cut here---------------start------------->8---
$ guix build emacs-magit --with-input=emacs-no-x=emacs-next -n
substitute: updating substitutes from 'https://ci.guix.gnu.org'... 100.0%
The following derivations would be built:
   /gnu/store/c7g5f6xgljj63n69dilvxmkgsdarflj2-emacs-magit-2.90.1-6.7f486d4.drv
   
/gnu/store/aanmy6ma51yc3ivfmzp8iakirmg2hclb-emacs-libgit-20200515-1.0ef8b13.drv
43.2 MB would be downloaded:
   /gnu/store/bvhvqv99ylyam8gv77ipa9qrgr6659ly-emacs-no-x-27.1
   
/gnu/store/j5vhj85bn6adkmlnfc6w7rikss6753d3-emacs-libgit-20200515-1.0ef8b13.tar.xz
   /gnu/store/0w02d2pxhjwfa6674fwq5asv6w7xdkrp-jsoncpp-1.9.2
   /gnu/store/nlia3wcilwsdj8q883bgjmzirs6yl8z7-rhash-1.3.9
   /gnu/store/89rj5fqcg48afgk99639ds602pgf92k4-cmake-minimal-3.16.5
   /gnu/store/mhlxiw0fgv5mbqsml433f34349xdlmn3-module-import-compiled
   
/gnu/store/gk7gh5ik9f4ng35k22pz49r75vkhcbk8-emacs-magit-2.90.1-6.7f486d4-checkout
--8<---------------cut here---------------end--------------->8---


And it is expected because ’package-mapping’ only “rewrites” the
’inputs:

--8<---------------cut here---------------start------------->8---
              (inputs (map rewrite (package-inputs p)))
              (native-inputs (map rewrite (package-native-inputs p)))
              (propagated-inputs (map rewrite (package-propagated-inputs p)))
              (replacement (and=> (package-replacement p) replace))
--8<---------------cut here---------------end--------------->8---


Do I miss something?


All the best,
simon

[1] <http://issues.guix.gnu.org/issue/43578>