From dedb512f8f2282f7de3d5b56e7551e486e37840c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Mon, 16 Oct 2017 09:57:44 +0200
Subject: gexp: Add 'file-union'.

* gnu/services.scm (file-union): Move to...
* guix/gexp.scm (file-union): ... here.  New procedure.
* doc/guix.texi (G-Expressions): Document it.
---
 guix/gexp.scm | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

(limited to 'guix/gexp.scm')

diff --git a/guix/gexp.scm b/guix/gexp.scm
index 2622c5cb62..9835599bb8 100644
--- a/guix/gexp.scm
+++ b/guix/gexp.scm
@@ -78,6 +78,7 @@
             gexp->script
             text-file*
             mixed-text-file
+            file-union
             imported-files
             imported-modules
             compiled-modules
@@ -1171,6 +1172,37 @@ This is the declarative counterpart of 'text-file*'."
 
   (computed-file name build))
 
+(define (file-union name files)
+  "Return a <computed-file> that builds a directory containing all of FILES.
+Each item in FILES must be a two-element list where the first element is the
+file name to use in the new directory, and the second element is a gexp
+denoting the target file.  Here's an example:
+
+  (file-union \"etc\"
+              `((\"hosts\" ,(plain-file \"hosts\"
+                                        \"127.0.0.1 localhost\"))
+                (\"bashrc\" ,(plain-file \"bashrc\"
+                                         \"alias ls='ls --color'\"))))
+
+This yields an 'etc' directory containing these two files."
+  (computed-file name
+                 (gexp
+                  (begin
+                    (mkdir (ungexp output))
+                    (chdir (ungexp output))
+                    (ungexp-splicing
+                     (map (match-lambda
+                            ((target source)
+                             (gexp
+                              (begin
+                                ;; Stat the source to abort early if it does
+                                ;; not exist.
+                                (stat (ungexp source))
+
+                                (symlink (ungexp source)
+                                         (ungexp target))))))
+                          files))))))
+
 
 ;;;
 ;;; Syntactic sugar.
-- 
cgit v1.2.3