gexp: Remove special meaning of forms (PACKAGE OUTPUT) in ungexp.

* guix/gexp.scm (gexp-inputs)[add-reference-inputs]: Remove clause for
  inputs of the form (PACKAGE OUTPUT).
  (gexp->sexp)[reference->sexp]: Likewise.
* tests/gexp.scm ("input list splicing"): Change 'list' to 'gexp-input'
  for glibc:debug.
  ("text-file*"): Likewise for %bootstrap-guile:out.
  ("input list splicing + gexp-input + ungexp-native-splicing"): Remove,
  now redundant.

gexp: Export 'gexp-input' constructor.

* guix/gexp.scm (<gexp-input>)[gexp-input]: Rename to...
  [%gexp-input]: ... this.  Adjust callers accordingly.
  (gexp-input): New procedure.
  (gexp-inputs)[add-reference-inputs]: When the input is a list, check
  whether each item is already 'gexp-input?' and to not rewrap those.
  (gexp-outputs)[add-reference-output]: Likewise.
  (gexp->sexp): Likewise.
* tests/gexp.scm ("input list splicing + gexp-input +
  ungexp-native-splicing"): New test.

tests: Add an indirection for white-box testing.

* tests/gexp.scm (gexp-inputs, gexp-native-inputs, gexp-outputs,
  gexp->sexp): Make an indirection, to facilitate live testing with
  Geiser.

Merge branch 'core-updates'.

gexp: Make sure 'gexp-outputs' removes duplicate outputs.

Fixes a regression introduced in f9efe56.

* guix/gexp.scm (gexp-outputs): Add call to 'delete-duplicates'.
* tests/gexp.scm ("output list, combined gexps, duplicate output"): New
  test.

gexp: Aggregate outputs of compound gexps.

* guix/gexp.scm (gexp-outputs)[add-reference-output]: Recurse into
  lists.
* tests/gexp.scm ("output list + ungexp-splicing list, combined gexps"):
  New test.

gexp: Add tests for 'gexp-outputs'.

* tests/gexp.scm (gexp-outputs): New procedure.
  ("output list", "output list, combined gexps"): New tests.

Merge branch 'master' into core-updates

gexp: Add #:graft? parameter to 'gexp->derivation'.

* guix/gexp.scm (gexp->derivation): Add #:graft? parameter and honor it.
* tests/gexp.scm ("gexp->derivation vs. grafts"): New test.
* doc/guix.texi (G-Expressions): Update 'gexp->derivation'
  documentation.

gexp: Implement 'imported-modules' & co. using 'gexp->derivation'.

* guix/derivations.scm (imported-files): Keep private.
  (%imported-modules, %compiled-modules, build-expression->derivation):
  Mark as deprecated.
  (imported-modules, compiled-modules): Remove.
* guix/gexp.scm (%mkdir-p-definition): New variable.
  (imported-files, search-path*, imported-modules, compiled-modules):
  New procedures.
* tests/derivations.scm ("imported-files"): Remove.
* tests/gexp.scm ("imported-files", "gexp->derivation #:modules"): New
  tests.

Merge branch 'master' into core-updates

gexp: Add #:allowed-references parameter to 'gexp->derivation'.

* guix/gexp.scm (lower-references): New procedure.
  (gexp->derivation): Add #:allowed-references and honor it.
* tests/gexp.scm ("gexp->derivation #:allowed-references",
  "gexp->derivation #:allowed-references, disallowed"): New tests.
* doc/guix.texi (G-Expressions): Update 'gexp->derivation' doc.

Merge branch 'master' into core-updates

monads: Rewrite 'text-file*' using gexps.

* guix/monads.scm (text-file*): Move to...
* guix/gexp.scm (text-file*): ... here.  Rewrite using gexps.
* tests/monads.scm ("text-file*"): Move to...
* tests/gexp.scm ("text-file*"): ... here.

Merge branch 'master' into core-updates

gexp: Allow use of high-level objects in #:references-graphs.

* guix/gexp.scm (lower-reference-graphs): New procedure.
  (gexp->derivation)[graphs-file-names]: New procedure.
  Use 'lower-reference-graphs', and augment #:inputs argument as a
  function of #:references-graphs.
* doc/guix.texi (G-Expressions): Adjust 'gexp->derivation' documentation
  accordingly.
* tests/gexp.scm ("gexp->derivation, store copy"): Remove reference to
  TWO in BUILD-DRV.  Use TWO directly in #:references-graphs argument.
  ("gexp->derivation #:references-graphs"): New test.
* gnu/system/vm.scm (qemu-image): Remove variable 'graph'; use INPUTS as
  the #:references-graphs argument to
  'expression->derivation-in-linux-vm'.

vm: Move store copy handling to (guix build store-copy).

* gnu/build/vm.scm (read-reference-graph, populate-store): Move to...
* guix/build/store-copy.scm: ... here.  New file.
* Makefile.am (MODULES): Add it.
* gnu/system/vm.scm (expression->derivation-in-linux-vm): Adjust default
  #:modules values accordingly.
* tests/gexp.scm ("gexp->derivation, store copy"): New test.

Merge branch 'master' into core-updates

Factorize test suite support in (guix tests).

* guix/tests.scm: New file.
* Makefile.am (noinst_DATA): New variable.
  (GOBJECTS): Add guix/tests.go.
* tests/builders.scm (%store): Use 'open-connection-for-tests'
  from (guix tests).
* tests/derivations.scm: Likewise.
* tests/monads.scm: Likewise.
* tests/packages.scm: Likewise.
* tests/profiles.scm: Likewise.
* tests/union.scm: Likewise.
* tests/gexp.scm: Likewise.
  (guile-for-build): Remove.  Use (%guile-for-build) instead.
* tests/nar.scm (make-random-bytevector, %seed, random-text): Remove.
  (populate-file): Change 'make-random-bytevector' to 'random-bytevector'.
  Use (guix tests).
* tests/store.scm (%seed, random-text): Remove.
  Use (guix tests).

Merge branch 'master' into core-updates