Hi Guix,

I'm trying to define a fixed output derivation using gexp->derivation,
but I'm getting a hash mismatch, and I can't figure out why.  I've
attached a minimal script that illustrates the problem.  When I run it,
I see the following output:

--8<---------------cut here---------------start------------->8---
$ /tmp/test-fixed-output-derivation.scm 
;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
;;;       or pass the --no-auto-compile argument to disable.
;;; compiling /tmp/test-fixed-output-derivation.scm
;;; compiled /home/marusich/.cache/guile/ccache/2.2-LE-8-3.A/tmp/test-fixed-output-derivation.scm.go
The following derivation will be built:
   /gnu/store/fiiz8cxz90q7l0c6jfdrpzkanyyvhpv8-test.drv
building path(s) `/gnu/store/8s4m28x6qmpkqhqasy59lw3hih548kxv-test'
`/gnu/store/kfzwabhn37bg692ayb2czb853drlv2gp-test' -> `/gnu/store/8s4m28x6qmpkqhqasy59lw3hih548kxv-test'
sha256 hash mismatch for output path `/gnu/store/8s4m28x6qmpkqhqasy59lw3hih548kxv-test'
  expected: 0dids4n73p8w77pn9nffs7x0ww1a3f1jbic1p642hwd0jfl3zcg9
  actual:   1r3v22qkypccqifzbww5lrn6hf1chi23m6zzkyvb8bvg457nxslq
Backtrace:
           8 (apply-smob/1 #<catch-closure 2507640>)
In ice-9/boot-9.scm:
    705:2  7 (call-with-prompt _ _ #<procedure default-prompt-handle…>)
In ice-9/eval.scm:
    619:8  6 (_ #(#(#<directory (guile-user) 25be140>)))
In ice-9/boot-9.scm:
   2312:4  5 (save-module-excursion _)
  3822:12  4 (_)
In /tmp/test-fixed-output-derivation.scm:
     30:2  3 (_)
In guix/store.scm:
  1443:24  2 (run-with-store _ _ #:guile-for-build _ #:system _ # _)
  1362:38  1 (_ #<build-daemon 256.97 2bd1eb0>)
   936:15  0 (_ #<build-daemon 256.97 2bd1eb0> _ _)

guix/store.scm:936:15: Throw to key `srfi-34' with args `(#<condition &nix-protocol-error [message: "build of `/gnu/store/fiiz8cxz90q7l0c6jfdrpzkanyyvhpv8-test.drv' failed" status: 1] 33c9030>)'.
--8<---------------cut here---------------end--------------->8---

I don't understand why the Guix daemon thinks that the output
(/gnu/store/8s4m28x6qmpkqhqasy59lw3hih548kxv-test) hashes to
0dids4n73p8w77pn9nffs7x0ww1a3f1jbic1p642hwd0jfl3zcg9.  That doesn't even
match what "guix hash" says:

  $ guix hash /gnu/store/8s4m28x6qmpkqhqasy59lw3hih548kxv-test
  1r3v22qkypccqifzbww5lrn6hf1chi23m6zzkyvb8bvg457nxslq
  $ guix hash --recursive /gnu/store/8s4m28x6qmpkqhqasy59lw3hih548kxv-test
  1xmr8jicvzszfzpz46g37mlpvbzjl2wpwvl2b05psipssyp1sm8h

Note that the result of "guix hash" above DOES match the hash value for
/tmp/test:

  $ guix hash /tmp/test
  1r3v22qkypccqifzbww5lrn6hf1chi23m6zzkyvb8bvg457nxslq
  $ guix hash --recursive /tmp/test
  1xmr8jicvzszfzpz46g37mlpvbzjl2wpwvl2b05psipssyp1sm8h

What's going on here?  No matter what I try (e.g., change recursive? to
#t), I can't seem to escape this hash mismatch.  I think I'm missing
something obvious, but I can't see what.  I'd really appreciate a second
pair of eyes!

-- 
Chris