emacs: devel: Add indentation rules.

Suggested by Ludovic Courtès <ludo@gnu.org>.

* emacs/guix-devel.el: Add indentation rules for Guix macros/procedures.
  (guix-devel-scheme-indent): New macro.
  (guix-devel-indent-package): New function.

emacs/guix-devel.el

@@ -24,6 +24,7 @@
 
 ;;; Code:
 
+(require 'lisp-mode)
 (require 'guix-guile)
 (require 'guix-geiser)
 (require 'guix-utils)
@@ -188,6 +189,69 @@ to find 'modify-phases' keywords."
       (0 'guix-devel-modify-phases-keyword nil t))))
   "A list of `font-lock-keywords' for `guix-devel-mode'.")
 
+
+;;; Indentation
+
+(defmacro guix-devel-scheme-indent (&rest rules)
+  "Set `scheme-indent-function' according to RULES.
+Each rule should have a form (SYMBOL VALUE).  See `put' for details."
+  (declare (indent 0))
+  `(progn
+     ,@(mapcar (lambda (rule)
+                 `(put ',(car rule) 'scheme-indent-function ,(cadr rule)))
+               rules)))
+
+(defun guix-devel-indent-package (state indent-point normal-indent)
+  "Indentation rule for 'package' form."
+  (let* ((package-eol (line-end-position))
+         (count (if (and (ignore-errors (down-list) t)
+                         (< (point) package-eol)
+                         (looking-at "inherit\\>"))
+                    1
+                  0)))
+    (lisp-indent-specform count state indent-point normal-indent)))
+
+(guix-devel-scheme-indent
+  (bag 0)
+  (build-system 0)
+  (call-with-compressed-output-port 2)
+  (call-with-container 1)
+  (call-with-decompressed-port 2)
+  (call-with-error-handling 0)
+  (container-excursion 1)
+  (emacs-batch-edit-file 1)
+  (emacs-batch-eval 0)
+  (emacs-substitute-sexps 1)
+  (emacs-substitute-variables 1)
+  (file-system 0)
+  (graft 0)
+  (manifest-entry 0)
+  (manifest-pattern 0)
+  (mbegin 1)
+  (mlet 2)
+  (mlet* 2)
+  (modify-phases 1)
+  (munless 1)
+  (mwhen 1)
+  (operating-system 0)
+  (origin 0)
+  (package 'guix-devel-indent-package)
+  (run-with-state 1)
+  (run-with-store 1)
+  (signature-case 1)
+  (substitute* 1)
+  (substitute-keyword-arguments 1)
+  (test-assertm 1)
+  (with-atomic-file-output 1)
+  (with-derivation-narinfo 1)
+  (with-derivation-substitute 2)
+  (with-directory-excursion 1)
+  (with-error-handling 0)
+  (with-monad 1)
+  (with-mutex 1)
+  (with-store 1)
+  (wrap-program 1))
+
 
 (defvar guix-devel-keys-map
   (let ((map (make-sparse-keymap)))