search-paths: Allow specs with #f as their separator.

This adds support for single-entry search paths.
Fixes <http://bugs.gnu.org/25422>.
Reported by Leo Famulari <leo@famulari.name>.

* guix/search-paths.scm (<search-path-specification>)[separator]:
Document as string or #f.
(evaluate-search-paths): Add case for SEPARATOR as #f.
(environment-variable-definition): Handle SEPARATOR being #f.
* guix/build/utils.scm (list->search-path-as-string): Add case for
SEPARATOR as #f.
(search-path-as-string->list): Likewise.
* guix/build/profiles.scm (abstract-profile): Likewise.
* tests/search-paths.scm: New file.
* Makefile.am (SCM_TESTS): Add it.
* tests/packages.scm ("--search-paths with single-item search path"):
New test.
* gnu/packages/version-control.scm (git)[native-search-paths](separator):
New field.

3 files changed, 44 insertions, 21 deletions

diff --git a/guix/build/profiles.scm b/guix/build/profiles.scm
index 6e316d5d2c..42eabfaf19 100644
--- a/guix/build/profiles.scm
+++ b/guix/build/profiles.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2015 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2015, 2017 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -39,17 +39,21 @@
 'GUIX_PROFILE' environment variable.  This allows users to specify what the
 user-friendly name of the profile is, for instance ~/.guix-profile rather than
 /gnu/store/...-profile."
-  (let ((replacement (string-append "${GUIX_PROFILE:-" profile "}")))
+  (let ((replacement (string-append "${GUIX_PROFILE:-" profile "}"))
+        (crop        (cute string-drop <> (string-length profile))))
     (match-lambda
       ((search-path . value)
-       (let* ((separator (search-path-specification-separator search-path))
-              (items     (string-tokenize* value separator))
-              (crop      (cute string-drop <> (string-length profile))))
-         (cons search-path
-               (string-join (map (lambda (str)
-                                   (string-append replacement (crop str)))
-                                 items)
-                            separator)))))))
+       (match (search-path-specification-separator search-path)
+         (#f
+          (cons search-path
+                (string-append replacement (crop value))))
+         ((? string? separator)
+          (let ((items (string-tokenize* value separator)))
+            (cons search-path
+                  (string-join (map (lambda (str)
+                                      (string-append replacement (crop str)))
+                                    items)
+                               separator)))))))))
 
 (define (write-environment-variable-definition port)
   "Write the given environment variable definition to PORT."
diff --git a/guix/build/utils.scm b/guix/build/utils.scm
index bc6f114152..cf09326393 100644
--- a/guix/build/utils.scm
+++ b/guix/build/utils.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2013 Andreas Enge <andreas@enge.fr>
 ;;; Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
 ;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
@@ -400,10 +400,17 @@ for under the directories designated by FILES.  For example:
               (delete-duplicates input-dirs)))
 
 (define (list->search-path-as-string lst separator)
-  (string-join lst separator))
+  (if separator
+      (string-join lst separator)
+      (match lst
+        ((head rest ...) head)
+        (() ""))))
 
 (define* (search-path-as-string->list path #:optional (separator #\:))
-  (string-tokenize path (char-set-complement (char-set separator))))
+  (if separator
+      (string-tokenize path
+                       (char-set-complement (char-set separator)))
+      (list path)))
 
 (define* (set-path-environment-variable env-var files input-dirs
                                         #:key
diff --git a/guix/search-paths.scm b/guix/search-paths.scm
index 7a6fe67959..4bf0e44389 100644
--- a/guix/search-paths.scm
+++ b/guix/search-paths.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013, 2014, 2015, 2017 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -55,7 +55,7 @@
   search-path-specification?
   (variable     search-path-specification-variable) ;string
   (files        search-path-specification-files)    ;list of strings
-  (separator    search-path-specification-separator ;string
+  (separator    search-path-specification-separator ;string | #f
                 (default ":"))
   (file-type    search-path-specification-file-type ;symbol
                 (default 'directory))
@@ -131,11 +131,23 @@ like `string-tokenize', but SEPARATOR is a string."
 DIRECTORIES, a list of directory names, and return a list of
 specification/value pairs.  Use GETENV to determine the current settings and
 report only settings not already effective."
-  (define search-path-definition
-    (match-lambda
-      ((and spec
-            ($ <search-path-specification> variable files separator
-                                           type pattern))
+  (define (search-path-definition spec)
+    (match spec
+      (($ <search-path-specification> variable files #f type pattern)
+       ;; Separator is #f so return the first match.
+       (match (with-null-error-port
+               (search-path-as-list files directories
+                                    #:type type
+                                    #:pattern pattern))
+         (()
+          #f)
+         ((head . _)
+          (let ((value (getenv variable)))
+            (if (and value (string=? value head))
+                #f                         ;VARIABLE already set appropriately
+                (cons spec head))))))
+      (($ <search-path-specification> variable files separator
+                                      type pattern)
        (let* ((values (or (and=> (getenv variable)
                                  (cut string-tokenize* <> separator))
                           '()))
@@ -164,7 +176,7 @@ current value), or 'suffix (return the definition where VALUE is added as a
 suffix to VARIABLE's current value.)  In the case of 'prefix and 'suffix,
 SEPARATOR is used as the separator between VARIABLE's current value and its
 prefix/suffix."
-  (match kind
+  (match (if (not separator) 'exact kind)
     ('exact
      (format #f "export ~a=\"~a\"" variable value))
     ('prefix