bug#19364: search-patch fails to consult GUIX_PACKAGE_PATH

[Ludovic Courtès]

Mark H Weaver <address@hidden> skribis:

> Tomáš Čech <address@hidden> reported on IRC that 'search-patch'
> failed to find a patch he had put into DIR/gnu/packages/patches/, where
> DIR was in $GUIX_PACKAGE_PATH.  Adding DIR to GUILE_LOAD_PATH fixed the
> problem.

Fixed in ee06af5.

> Also, it would be good to improve the error message when 'search-patch'
> fails.  This is what he reported seeing:
>
> guix/packages.scm:374:17: In procedure #<procedure 47c70c0 at 
> guix/packages.scm:372:9 (number patch)>:
> guix/packages.scm:374:17: Throw to key `match-error' with args `("match" "no 
> matching pattern" #f)'.

I came up with this patch:

diff --git a/gnu/packages.scm b/gnu/packages.scm
index 7f0b58b..57a3e21 100644
--- a/gnu/packages.scm
+++ b/gnu/packages.scm
@@ -30,6 +30,8 @@
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-11)
   #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-34)
+  #:use-module (srfi srfi-35)
   #:use-module (srfi srfi-39)
   #:export (search-patch
             search-bootstrap-binary
@@ -70,13 +72,23 @@
         %load-path)))
 
 (define (search-patch file-name)
-  "Search the patch FILE-NAME."
-  (search-path (%patch-path) file-name))
+  "Search the patch FILE-NAME.  Raise an error if not found."
+  (or (search-path (%patch-path) file-name)
+      (raise (condition
+              (&message (message (format #f (_ "~a: patch not found")
+                                         file-name)))))))
 
 (define (search-bootstrap-binary file-name system)
-  "Search the bootstrap binary FILE-NAME for SYSTEM."
-  (search-path (%bootstrap-binaries-path)
-               (string-append system "/" file-name)))
+  "Search the bootstrap binary FILE-NAME for SYSTEM.  Raise an error if not
+found."
+  (or (search-path (%bootstrap-binaries-path)
+                   (string-append system "/" file-name))
+      (raise (condition
+              (&message
+               (message
+                (format #f (_ "could not find bootstrap binary '~a' \
+for system '~a'")
+                        file-name system)))))))
 
 (define %distro-root-directory
   ;; Absolute file name of the module hierarchy.

However, since ‘search-patch’ errors happen at load time, the actual
exception is hidden, and one just gets a “package not found” error.

To fix that, we’d need to make ‘patches’ a thunked field, which sounds
reasonable to me.  WDYT?

Thanks,
Ludo’.