[bug#71981] [PATCH] services: configuration: Produce doc even if package->symbol fails.

[Tomas Volf <~@wolfsden.cz>]

Due to #71979 it can happen that package->symbol can return #f even for
packages that are defined in modules on the load patch and which were
previously loaded and set as a default value.

In that case we can just return (package-name val), since for the purpose of
illustrating the default value in the documentation the name should suffice.
And having (possibly) slightly misleading documentation property is still
better then `guix pull' just failing due to passing #f to symbol->string.

* gnu/services/configuration.scm (generate-documentation)[package?]: Fall back
to package-name if package->symbol fails.

Change-Id: I9987caf40d3ff62a52cbd6e3325aa42c69a6c47a
---
 gnu/services/configuration.scm | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
index d2b1687496..a0e6fe206f 100644
--- a/gnu/services/configuration.scm
+++ b/gnu/services/configuration.scm
@@ -445,7 +445,14 @@ (define (generate-documentation documentation documentation-name)
                    (define (show-default val)
                      (cond
                       ((package? val)
-                       (symbol->string (package->symbol val)))
+                       (let ((sym (package->symbol val)))
+                         ;; Work around for #71979.  While in the alternate
+                         ;; the answer will not always match the symbol, it
+                         ;; should be good enough for illustrating the default
+                         ;; value in documentation.
+                         (if sym
+                             (symbol->string sym)
+                             (package-name val))))
                       (((list-of package?) val)
                        (format #f "(~{~a~^ ~})" (map package->symbol val)))
                       (else (str val))))
-- 
2.45.1