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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU 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.
;;;
;;; GNU 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 GNU 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 (ice-9 format)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-26)
#:export (tree-union
delete-duplicate-leaves
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* (delete-duplicate-leaves tree
#:optional
(leaf=? equal?)
(delete-duplicates (match-lambda
((head _ ...) head))))
"Delete duplicate leaves from TREE. Two leaves are considered equal
when LEAF=? applied to them returns #t. Each collision (list of leaves
that are LEAF=?) is passed to DELETE-DUPLICATES, which must return a
single leaf."
(let loop ((tree tree))
(match tree
((dir children ...)
(let ((dirs (filter pair? children))
(leaves (remove pair? children)))
(define collisions
(fold (lambda (leaf result)
(define same?
(cut leaf=? leaf <>))
(if (any (cut find same? <>) result)
result
(match (filter same? leaves)
((_)
result)
((collision ...)
(cons collision result)))))
'()
leaves))
(define non-collisions
(filter (lambda (leaf)
(match (filter (cut leaf=? leaf <>) leaves)
((_) #t)
((_ _ ..1) #f)))
leaves))
`(,dir
,@non-collisions
,@(map delete-duplicates collisions)
,@(map loop dirs))))
(leaf leaf))))
(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)))
(define (leaf=? a b)
(equal? (basename a) (basename b)))
(define (resolve-collision leaves)
;; LEAVES all have the same basename, so choose one of them.
(match (delete-duplicates leaves string=?)
((one-and-the-same)
;; LEAVES all actually point to the same file, so nothing to worry
;; about.
one-and-the-same)
((and lst (head _ ...))
;; A real collision.
(format (current-error-port) "warning: collision encountered: ~{~a ~}~%"
lst)
;; TODO: Implement smarter strategies.
(format (current-error-port) "warning: arbitrarily choosing ~a~%"
head)
head)))
(setvbuf (current-output-port) _IOLBF)
(setvbuf (current-error-port) _IOLBF)
(mkdir output)
(let loop ((tree (delete-duplicate-leaves
(cons "."
(tree-union (append-map (compose tree-leaves file-tree)
directories)))
leaf=?
resolve-collision))
(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.
(unless (string=? subdir ".")
(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
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