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-rw-r--r--guix/build/union.scm116
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+;;; 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