3 files changed, 222 insertions, 1 deletions

diff --git a/Makefile.am b/Makefile.am
index 10f3b617021..75e479ddc49 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -34,6 +34,7 @@ MODULES =					\
   guix/build/ftp.scm                            \
   guix/build/http.scm                           \
   guix/build/utils.scm                          \
+  guix/build/union.scm                          \
   guix/packages.scm                             \
   guix.scm                                      \
   distro.scm                                    \
@@ -116,7 +117,8 @@ TESTS =						\
   tests/derivations.scm                         \
   tests/utils.scm                               \
   tests/build-utils.scm                         \
-  tests/packages.scm
+  tests/packages.scm                            \
+  tests/union.scm
 
 LOG_COMPILER =                                  \
   $(top_builddir)/pre-inst-env                  \
diff --git a/guix/build/union.scm b/guix/build/union.scm
new file mode 100644
index 00000000000..ffd367917ae
--- /dev/null
+++ b/guix/build/union.scm
@@ -0,0 +1,116 @@
+;;; Guix --- Nix package management from Guile.         -*- coding: utf-8 -*-
+;;; Copyright (C) 2012 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of Guix.
+;;;
+;;; Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build union)
+  #:use-module (ice-9 ftw)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:export (tree-union
+            union-build))
+
+;;; Commentary:
+;;;
+;;; Build a directory that is the union of a set of directories, using
+;;; symbolic links.
+;;;
+;;; Code:
+
+(define (tree-union trees)
+  "Return a tree that is the union of the trees listed in TREES.  Each
+tree has the form (PARENT LEAVES ...) or just LEAF, where each leaf is
+itself a tree. "
+  (let loop ((trees trees))
+    (match trees
+      (()                                         ; nothing left
+       '())
+      (_
+       (let ((dirs   (filter pair? trees))
+             (leaves (remove pair? trees)))
+         `(,@leaves
+           ,@(fold (lambda (dir result)
+                     (cons `(,dir
+                             ,@(loop
+                                (concatenate
+                                 (filter-map (match-lambda
+                                              ((head children ...)
+                                               (and (equal? head dir)
+                                                    children)))
+                                             dirs))))
+                           result))
+                   '()
+                   (delete-duplicates (map car dirs)))))))))
+
+(define* (union-build output directories)
+  "Build in the OUTPUT directory a symlink tree that is the union of all
+the DIRECTORIES."
+  (define (file-tree dir)
+    ;; Return the contents of DIR as a tree.
+    (match (file-system-fold (const #t)
+                             (lambda (file stat result) ; leaf
+                               (match result
+                                 (((siblings ...) rest ...)
+                                  `((,file ,@siblings) ,@rest))))
+                             (lambda (dir stat result)  ; down
+                               `(() ,@result))
+                             (lambda (dir stat result)  ; up
+                               (match result
+                                 (((leaves ...) (siblings ...) rest ...)
+                                  `(((,(basename dir) ,@leaves) ,@siblings)
+                                    ,@rest))))
+                             (const #f)                 ; skip
+                             (lambda (file stat errno result)
+                               (format (current-error-port) "union-build: ~a: ~a~%"
+                                       file (strerror errno)))
+                             '(())
+                             dir)
+      (((tree)) tree)
+      (()       #f)))
+
+  (define tree-leaves
+    ;; Return the leaves of the given tree.
+    (match-lambda
+     (((? string?) leaves ...)
+      leaves)))
+
+  (setvbuf (current-output-port) _IOLBF)
+  (setvbuf (current-error-port) _IOLBF)
+
+  (mkdir output)
+  (let loop ((tree (tree-union (append-map (compose tree-leaves file-tree)
+                                           directories)))
+             (dir  '()))
+    (match tree
+      ((? string?)
+       ;; A leaf: create a symlink.
+       (let* ((dir    (string-join dir "/"))
+              (target (string-append output "/" dir "/" (basename tree))))
+         (format (current-error-port) "`~a' ~~> `~a'~%"
+                 tree target)
+         (symlink tree target)))
+      (((? string? subdir) leaves ...)
+       ;; A sub-directory: create it in OUTPUT, and iterate over LEAVES.
+       (let ((dir (string-join dir "/")))
+         (mkdir (string-append output "/" dir "/" subdir)))
+       (for-each (cute loop <> `(,@dir ,subdir))
+                 leaves))
+      ((leaves ...)
+       ;; A series of leaves: iterate over them.
+       (for-each (cut loop <> dir) leaves)))))
+
+;;; union.scm ends here
diff --git a/tests/union.scm b/tests/union.scm
new file mode 100644
index 00000000000..f8a58d59527
--- /dev/null
+++ b/tests/union.scm
@@ -0,0 +1,103 @@
+;;; Guix --- Nix package management from Guile.         -*- coding: utf-8 -*-
+;;; Copyright (C) 2012 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of Guix.
+;;;
+;;; Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+
+(define-module (test-union)
+  #:use-module (guix store)
+  #:use-module (guix utils)
+  #:use-module (guix derivations)
+  #:use-module (guix packages)
+  #:use-module (guix build union)
+  #:use-module ((guix build utils)
+                #:select (with-directory-excursion directory-exists?))
+  #:use-module (srfi srfi-64)
+  #:use-module (ice-9 match))
+
+;; Exercise the (guix build union) module.
+
+(define %store
+  (false-if-exception (open-connection)))
+
+(define %bootstrap-guile
+  (@@ (distro packages base) %bootstrap-guile))
+
+(when %store
+  ;; By default, use %BOOTSTRAP-GUILE for the current system.
+  (let ((drv (package-derivation %store %bootstrap-guile)))
+    (%guile-for-build drv)))
+
+
+(test-begin "union")
+
+(test-equal "tree-union, empty"
+  '()
+  (tree-union '()))
+
+(test-equal "tree-union, leaves only"
+  '(a b c d)
+  (tree-union '(a b c d)))
+
+(test-equal "tree-union, simple"
+  '((bin ls touch make awk gawk))
+  (tree-union '((bin ls touch)
+                (bin make)
+                (bin awk gawk))))
+
+(test-equal "tree-union, several levels"
+  '((share (doc (make README) (coreutils README)))
+    (bin ls touch make))
+  (tree-union '((bin ls touch)
+                (share (doc (coreutils README)))
+                (bin make)
+                (share (doc (make README))))))
+
+(test-skip (if %store 0 1))
+
+(test-assert "union-build"
+  (let* ((inputs  (map (match-lambda
+                        ((name package)
+                         `(,name ,(package-derivation %store package))))
+                       (@@ (distro packages base) %bootstrap-inputs)))
+         (builder `(begin
+                     (use-modules (guix build union))
+                     (union-build (assoc-ref %outputs "out")
+                                  (map cdr %build-inputs))))
+         (drv
+          (build-expression->derivation %store "union-test"
+                                        (%current-system)
+                                        builder inputs
+                                        #:modules '((guix build union)))))
+    (and (build-derivations %store (list (pk 'drv drv)))
+         (with-directory-excursion (derivation-path->output-path drv)
+           (and (file-exists? "bin/touch")
+                (file-exists? "bin/gcc")
+                (file-exists? "bin/ld")
+                (file-exists? "lib/libc.so")
+                (directory-exists? "lib/gcc")
+                (file-exists? "include/unistd.h"))))))
+
+(test-end)
+
+
+(exit (= (test-runner-fail-count (test-runner-current)) 0))
+
+;;; Local Variables:
+;;; eval: (put 'test-assert 'scheme-indent-function 1)
+;;; eval: (put 'test-equal 'scheme-indent-function 1)
+;;; eval: (put 'call-with-input-string 'scheme-indent-function 1)
+;;; End: