bug#27284: [PATCH 6/8] union: Parametrize the symlink procedure .

["Ludovic Courtès" <ludo@gnu.org>]

* guix/gexp.scm (directory-union): Add #:hard-links and honor it.
* guix/build/union.scm (union-build): Add #:symlink parameter.
---
 guix/build/union.scm | 11 ++++++-----
 guix/gexp.scm        | 19 ++++++++++++++++---
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/guix/build/union.scm b/guix/build/union.scm
index 18167fa3e..256123c56 100644
--- a/guix/build/union.scm
+++ b/guix/build/union.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2016 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2014 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2017 Huang Ying <huang.ying.caritas@gmail.com>
 ;;;
@@ -78,11 +78,12 @@ identical, #f otherwise."
 
 (define* (union-build output inputs
                       #:key (log-port (current-error-port))
-                      (create-all-directories? #f))
+                      (create-all-directories? #f)
+                      (symlink symlink))
   "Build in the OUTPUT directory a symlink tree that is the union of all the
-INPUTS.  As a special case, if CREATE-ALL-DIRECTORIES?, creates the
-subdirectories in the output directory to make sure the caller can modify them
-later."
+INPUTS, using SYMLINK to create symlinks.  As a special case, if
+CREATE-ALL-DIRECTORIES?, creates the subdirectories in the output directory to
+make sure the caller can modify them later."
 
   (define (symlink* input output)
     (format log-port "`~a' ~~> `~a'~%" input output)
diff --git a/guix/gexp.scm b/guix/gexp.scm
index b9525603e..e8ac3dcdc 100644
--- a/guix/gexp.scm
+++ b/guix/gexp.scm
@@ -1204,13 +1204,24 @@ This yields an 'etc' directory containing these two files."
                                          (ungexp target))))))
                           files))))))
 
-(define (directory-union name things)
+(define* (directory-union name things
+                          #:key (copy? #f))
   "Return a directory that is the union of THINGS, where THINGS is a list of
 file-like objects denoting directories.  For example:
 
   (directory-union \"guile+emacs\" (list guile emacs))
 
-yields a directory that is the union of the 'guile' and 'emacs' packages."
+yields a directory that is the union of the 'guile' and 'emacs' packages.
+
+When COPY? is true, copy files instead of creating symlinks."
+  (define symlink
+    (if copy?
+        (gexp (lambda (old new)
+                (if (file-is-directory? old)
+                    (symlink old new)
+                    (copy-file old new))))
+        (gexp symlink)))
+
   (match things
     ((one)
      ;; Only one thing; return it.
@@ -1221,7 +1232,9 @@ yields a directory that is the union of the 'guile' and 'emacs' packages."
                       (gexp (begin
                               (use-modules (guix build union))
                               (union-build (ungexp output)
-                                           '(ungexp things)))))))))
+                                           '(ungexp things)
+
+                                           #:symlink (ungexp symlink)))))))))
 
 \f
 ;;;
-- 
2.14.2