packages: Sanitize %load-path used in %patch-path.

Having the Guix root trailed by a slash in the GUILE_LOAD_PATH would
previously cause %patch-path to not return an entry with the patches
sub-directory, leading to errors such as:

   While executing meta-command:
   ERROR:
     1. &formatted-message:
         format: "~a: patch not found\n"
         arguments: ("icecat-use-older-reveal-hidden-html.patch")

* gnu/packages.scm (strip-trailing-slash): New procedure.
(%patch-path): Use it to strip any trailing slash from the %load-path entries.

Fixes: <https://issues.guix.gnu.org/43818>.
Change-Id: I4e98860d3914c8731c8dc70d29441e794825ff76

1 files changed, 7 insertions, 1 deletions

diff --git a/gnu/packages.scm b/gnu/packages.scm
index d859feadf62..db6a6c21ae3 100644
--- a/gnu/packages.scm
+++ b/gnu/packages.scm
@@ -164,6 +164,12 @@ flags."
              %default-package-module-path
              channels-scm))))
 
+(define (strip-trailing-slash s)
+  ;; Strip the trailing slash of a string, if present.
+  (if (string-suffix? "/" s)
+      (string-drop-right s 1)
+      s))
+
 (define %patch-path
   ;; Define it after '%package-module-path' so that '%load-path' contains user
   ;; directories, allowing patches in $GUIX_PACKAGE_PATH to be found.
@@ -172,7 +178,7 @@ flags."
           (if (string=? directory %distro-root-directory)
               (string-append directory "/gnu/packages/patches")
               directory))
-        %load-path)))
+        (map strip-trailing-slash %load-path))))
 
 ;; This procedure is used by Emacs-Guix up to 0.5.1.1, so keep it for now.
 ;; See <https://github.com/alezost/guix.el/issues/30>.