09/10: build-system/haskell: Explain failure.

[guix-commits]

lbraun pushed a commit to branch wip-haskell
in repository guix.

commit c731961aa45a21c3720daf1be5494602665dd64b
Author: Lars-Dominik Braun <lars@6xq.net>
AuthorDate: Sun Sep 19 11:10:16 2021 +0200

    build-system/haskell: Explain failure.
    
    Provide human-readable failure message and explain how to fix it.
    
    * guix/build/haskell-build-system.scm (register): Raise error if source
    file does not exist.
---
 guix/build/haskell-build-system.scm | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/guix/build/haskell-build-system.scm 
b/guix/build/haskell-build-system.scm
index 4d0bf6f..ef6cb31 100644
--- a/guix/build/haskell-build-system.scm
+++ b/guix/build/haskell-build-system.scm
@@ -217,6 +217,8 @@ given Haskell package."
          (if (not (vhash-assoc id seen))
              (let ((dep-conf  (string-append src  "/" id ".conf"))
                    (dep-conf* (string-append dest "/" id ".conf")))
+               (when (not (file-exists? dep-conf))
+                   (error (format #f "File ~a does not exist. This usually 
means the dependency ~a is missing. Was checking conf-file ~a." dep-conf id 
conf-file)))
                (copy-file dep-conf dep-conf*) ;XXX: maybe symlink instead?
                (loop (vhash-cons id #t seen)
                      (append lst (conf-depends dep-conf))))