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-rw-r--r--guix/build/union.scm41
-rw-r--r--tests/union.scm18
-rw-r--r--tests/utils.scm2
3 files changed, 59 insertions, 2 deletions
diff --git a/guix/build/union.scm b/guix/build/union.scm
index 1179f1234b..82d6199d9e 100644
--- a/guix/build/union.scm
+++ b/guix/build/union.scm
@@ -27,7 +27,9 @@
#:use-module (rnrs io ports)
#:export (union-build
- warn-about-collision))
+ warn-about-collision
+
+ relative-file-name))
;;; Commentary:
;;;
@@ -174,4 +176,41 @@ returns #f, skip the faulty file altogether."
(union-of-directories output (delete-duplicates inputs)))
+
+;;;
+;;; Relative symlinks.
+;;;
+
+(define %not-slash
+ (char-set-complement (char-set #\/)))
+
+(define (relative-file-name reference file)
+ "Given REFERENCE and FILE, both of which are absolute file names, return the
+file name of FILE relative to REFERENCE.
+
+ (relative-file-name \"/gnu/store/foo\" \"/gnu/store/bin/bar\")
+ => \"../bin/bar\"
+
+Note that this is from a purely lexical standpoint; conversely, \"..\" is
+*not* resolved lexically on POSIX in the presence of symlinks."
+ (if (and (string-prefix? "/" file) (string-prefix? "/" reference))
+ (let loop ((reference (string-tokenize reference %not-slash))
+ (file (string-tokenize file %not-slash)))
+ (define (finish)
+ (string-join (append (make-list (length reference) "..") file)
+ "/"))
+
+ (match reference
+ (()
+ (finish))
+ ((head . tail)
+ (match file
+ (()
+ (finish))
+ ((head* . tail*)
+ (if (string=? head head*)
+ (loop tail tail*)
+ (finish)))))))
+ file))
+
;;; union.scm ends here
diff --git a/tests/union.scm b/tests/union.scm
index aa95cae001..5a6a4033fc 100644
--- a/tests/union.scm
+++ b/tests/union.scm
@@ -184,4 +184,22 @@
(file-is-directory? "bin")
(eq? 'symlink (stat:type (lstat "bin/guile"))))))))
+(letrec-syntax ((test-relative-file-name
+ (syntax-rules (=>)
+ ((_ (reference file => expected) rest ...)
+ (begin
+ (test-equal (string-append "relative-file-name "
+ reference " " file)
+ expected
+ (relative-file-name reference file))
+ (test-relative-file-name rest ...)))
+ ((_)
+ #t))))
+ (test-relative-file-name
+ ("/a/b" "/a/c/d" => "../c/d")
+ ("/a/b" "/a/b" => "")
+ ("/a/b" "/a" => "..")
+ ("/a/b" "/a/b/c/d" => "c/d")
+ ("/a/b/c" "/a/d/e/f" => "../../d/e/f")))
+
(test-end)
diff --git a/tests/utils.scm b/tests/utils.scm
index 035886dd16..197182acf7 100644
--- a/tests/utils.scm
+++ b/tests/utils.scm
@@ -1,5 +1,5 @@
;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2014 Eric Bavier <bavier@member.fsf.org>
;;; Copyright © 2016 Mathieu Lirzin <mthl@gnu.org>
;;;