guix package: Add '--export-channels'.

* guix/channels.scm (sexp->channel): Export.
* guix/describe.scm: Use (guix channels).
(manifest-entry-provenance): New procedure.
* guix/scripts/package.scm (channel=?, export-channels): New
procedures.
(show-help, %options): Add '--export-channels'.
(process-query): Honor it.
* build-aux/build-self.scm (build-program)[select?]: Exclude (guix
channels) to account for the (guix describe) change above.
* doc/guix.texi (Invoking guix package): Document it.

1 files changed, 3 insertions, 0 deletions

diff --git a/build-aux/build-self.scm b/build-aux/build-self.scm
index 4b6e2bfae52..d5bc5fb46e4 100644
--- a/build-aux/build-self.scm
+++ b/build-aux/build-self.scm
@@ -245,8 +245,11 @@ interface (FFI) of Guile.")
   "Return a program that computes the derivation to build Guix from SOURCE."
   (define select?
     ;; Select every module but (guix config) and non-Guix modules.
+    ;; Also exclude (guix channels): it is autoloaded by (guix describe), but
+    ;; only for peripheral functionality.
     (match-lambda
       (('guix 'config) #f)
+      (('guix 'channels) #f)
       (('guix _ ...)   #t)
       (('gnu _ ...)    #t)
       (_               #f)))