gnu: neovim: Add support for guix neovim packages.

Enables the use of guix as a package manager for neovim, compatible with
the outputs of `vim-build-system`.

* gnu/packages/vim.scm (neovim)[arguments]: Added another phase to
install the system init file to the correct place.
* gnu/packages/aux-files/guix-nvim.vim: New file.
* Makefile.am (AUX_FILES): Register file.

Change-Id: I375e3e0d051da27d065dff5456cb298a01bc90b1
Signed-off-by: Efraim Flashner <efraim@flashner.co.il>

Makefile.am

@@ -448,6 +448,7 @@ AUX_FILES =						\
   gnu/packages/aux-files/emacs/guix-emacs.el		\
   gnu/packages/aux-files/findclass.php			\
   gnu/packages/aux-files/guix.vim			\
+  gnu/packages/aux-files/guix-nvim.vim			\
   gnu/packages/aux-files/linux-libre/6.16-arm64.conf	\
   gnu/packages/aux-files/linux-libre/6.16-riscv.conf	\
   gnu/packages/aux-files/linux-libre/6.16-x86_64.conf	\

gnu/packages/aux-files/guix-nvim.vim

@@ -0,0 +1,10 @@
+lua << EOF
+  -- This appends all applicable neovim paths to the runtimepath.
+  for _, directory in pairs({"/run/current-system/profile", "~/.guix-profile", "~/.guix-home/profile", vim.env.GUIX_PROFILE, vim.env.GUIX_ENVIRONMENT}) do
+    local rtp = vim.fs.abspath(directory .. "/share/nvim/site")
+    local stat = vim.uv.fs_stat(rtp)
+    if stat and stat.type == "directory" then
+      vim.opt.rtp:append(rtp)
+    end
+  end
+EOF

gnu/packages/vim.scm

@@ -862,7 +862,15 @@ is based on Vim's builtin plugin support.")
                    ;; doubles its size.  We remove the reference here.
                    (substitute* "cmake.config/versiondef.h.in"
                      (("\\$\\{CMAKE_C_COMPILER\\}") "/gnu/store/.../bin/gcc"))
-                   #t)))))
+                   #t))
+               (add-after 'install 'install-guix-nvim.vim
+                 (lambda* (#:key outputs #:allow-other-keys)
+                   (let ((nvimdir (string-append (assoc-ref outputs "out")
+                                                 "/share/nvim")))
+                     (mkdir-p nvimdir)
+                     (copy-file
+                       #$(local-file (search-auxiliary-file "guix-nvim.vim"))
+                       (string-append nvimdir "/sysinit.vim"))))))))
     (inputs (list libuv-for-luv
                   msgpack
                   libtermkey