bug#20163: substitute-binary fails when attempting to reconfigure

[Mark H Weaver <mhw@netris.org>]

Running "guix system reconfigure" with substitutes enabled now
consistently fails for me with the following backtrace:

--8<---------------cut here---------------start------------->8---
root:~# ~mhw/bin/guix system reconfigure ~mhw/jojen.scm
substitute-binary: Backtrace:
substitute-binary: In ice-9/boot-9.scm:
substitute-binary:  157: 17 [catch #t #<catch-closure 9a45950> ...]
substitute-binary: In unknown file:
substitute-binary:    ?: 16 [apply-smob/1 #<catch-closure 9a45950>]
substitute-binary: In ice-9/boot-9.scm:
substitute-binary:   63: 15 [call-with-prompt prompt0 ...]
substitute-binary: In ice-9/eval.scm:
substitute-binary:  432: 14 [eval # #]
substitute-binary: In ice-9/boot-9.scm:
substitute-binary: 2401: 13 [save-module-excursion #<procedure 9a56ca0 at ice-9/boot-9.scm:4045:3 ()>]
substitute-binary: 4050: 12 [#<procedure 9a56ca0 at ice-9/boot-9.scm:4045:3 ()>]
substitute-binary: 1724: 11 [%start-stack load-stack ...]
substitute-binary: 1729: 10 [#<procedure 9a5b708 ()>]
substitute-binary: In unknown file:
substitute-binary:    ?: 9 [primitive-load "/gnu/store/lhwsnbq2h05m604zpw9wvglkaif8y41h-guix-0.8.1.07157e8/bin/guix"]
substitute-binary: In guix/ui.scm:
substitute-binary:  838: 8 [run-guix-command substitute-binary "--query"]
substitute-binary: In ice-9/boot-9.scm:
substitute-binary:  157: 7 [catch misc-error #<procedure 9e141f0 at guix/ui.scm:839:6 ()> ...]
substitute-binary: 2864: 6 [resolve-interface (guix scripts substitute-binary) #:select ...]
substitute-binary: 2789: 5 [#<procedure 99da000 at ice-9/boot-9.scm:2777:4 (name #:optional autoload version #:key ensure)> # ...]
substitute-binary: 3065: 4 [try-module-autoload (guix scripts substitute-binary) #f]
substitute-binary: 2401: 3 [save-module-excursion #<procedure 9e17870 at ice-9/boot-9.scm:3066:17 ()>]
substitute-binary: 3085: 2 [#<procedure 9e17870 at ice-9/boot-9.scm:3066:17 ()>]
substitute-binary: In unknown file:
substitute-binary:    ?: 1 [primitive-load-path "guix/scripts/substitute-binary" ...]
substitute-binary: In guix/scripts/substitute-binary.scm:
substitute-binary:  634: 0 [#<procedure 9e74470 ()>]
substitute-binary: 
substitute-binary: guix/scripts/substitute-binary.scm:634:2: In procedure #<procedure 9e74470 ()>:
substitute-binary: guix/scripts/substitute-binary.scm:634:2: Throw to key `match-error' with args `("match" "no matching pattern" ())'.
guix system: error: build failed: unexpected end-of-file
root:~#
--8<---------------cut here---------------end--------------->8---

Running the same command with --no-substitutes works:

--8<---------------cut here---------------start------------->8---
root:~# ~mhw/bin/guix system reconfigure ~mhw/jojen.scm --no-substitutes
The following derivations will be built:
   /gnu/store/zshpy31rx9bisi6w64hljrrysd0jqrk9-grub-2.00.drv
   /gnu/store/hm02q0iy3jjr995cgyy6pq0fjxkywm7i-grub.cfg.drv
   /gnu/store/gzylnn8kq40s9day9h3xassqv2jnbkck-grub-2.00.tar.xz.drv
   /gnu/store/ld352ranb4xl1x882zkl2ax8w4581xcl-xorriso-1.3.8.drv
   /gnu/store/pp5ci0lnd8ib9n3wkrpxj788zyrw6fla-qemu-headless-1.3.1.drv
   /gnu/store/5lhhp3ypph0vvdsp7fbfk07arr77c4ms-gtkmm-2.24.2.drv
   /gnu/store/vzxd6l9qxslnslgy538kxq6v7akbi25x-inkscape-0.91.drv
   /gnu/store/sdfydjqpbp2vr7p87cz35zxxhn7g25df-grub-image.png.drv
   /gnu/store/1y0xirbizfvj7p7ps2awlcb3vs35jsii-grub-image.resized.png.drv
grub-2.00/
grub-2.00/po/
grub-2.00/po/LINGUAS
grub-2.00/po/stamp-po
grub-2.00/po/grub.pot
[...]
--8<---------------cut here---------------end--------------->8---

Running other commands including "guix system build" and "guix package"
with substitutes enabled works properly.

The 'guix' command being run here is using 'pre-inst-env' within a git
checkout that's on 9d297fa but with some local commits added including
'wip-http-pipelining'.  The 'guix-daemon' being run is from
guix-0.8.1.07157e8, which I suppose is using its own copy of 'guix
substitute' (right?).

      Mark