guix package: '--delete-generations' deletes generations older than specified.

* guix/scripts/package.scm (matching-generations): Add
  'duration-relation' keyword parameter.
  (guix-package)[process-action](delete-generations): Pass
  #:duration-relation >.
* tests/guix-package.sh: Add test.
* doc/guix.texi (Invoking guix package): Clarify the meaning of
  durations for '--list-durations' and '--delete-durations'.

tests: Fix typo.

* tests/guix-package.sh: Add missing "-p" option.

build-system/trivial: Take the 'source' field into account.

* guix/build-system/trivial.scm (trivial-build): When SOURCE is true,
  add it to INPUTS.
  (trivial-cross-build): Likewise.
* tests/packages.scm ("trivial with source"): New test.

guix package: Add '--delete-generations'.

* guix/scripts/package.scm (switch-to-previous-generation): New function.
  (roll-back): Use the new function instead of 'switch-link'.
  (show-help): Add '--delete-generations'.
  (%options): Likewise.
  (guix-package)[process-actions]: Add 'current-generation-number',
  'display-and-delete', and 'delete-generation'.  Add support for
  '--delete-generations', and reindent the code.
* tests/guix-package.sh: Test '--delete-generations'.
* doc/guix.texi (Invoking guix-package): Document '--delete-generations'.

guix package: Show which generation is the current one.

* guix/scripts/package.scm (guix-package)[process-query]: Show that a
  generation is the current one if the profile points to it.
* tests/guix-package.sh: Test it.

tests: Use 'test -z' to check that a string equals zero.

guix package: Do not list the zeroth generation.

* guix/scripts/package.scm (guix-package)[process-query]: Change
  'list-generation' to not list the zeroth generation.
* tests/guix-package.sh: Test it.
* doc/guix.texi (Invoking guix package): Document it, and use the
  right term when talking about generations.

guix package: Exit with 1 when a generation cannot be listed.

* guix/scripts/package.scm (guix-package)[process-query]: Exit with 1
  when a generation does not exist or the profile points to the zeroth
  generation.
* tests/guix-package.sh: Test the former case.

guix-register: Expect closures to refer to the original store.

* nix/guix-register/guix-register.cc (prefix): New variable.
  (parse_opt): Use it.
  (register_validity): Change 'info.path' to the final store name.
  Hash the final under its real path.
* tests/guix-register.sh: Adjust the contents of $closure accordingly.
  Rename 'NIX_LOCALSTATE_DIR' to 'NIX_STATE_DIR'.  Don't try to call
  'valid-path?'.  Add test using 'sqlite3'.

Add 'guix-register'.

* nix/guix-register/guix-register.cc, tests/guix-register.sh: New
  files.
* Makefile.am (SH_TESTS)[BUILD_DAEMON]: Add tests/guix-register.sh.
* daemon.am (sbin_PROGRAMS, guix_register_SOURCES,
  guix_register_CPPFLAGS, guix_register_LDADD): New variables.
* test-env.in: Export 'storedir', 'prefix', 'datarootdir', 'datadir',
  and 'localstatedir'.

guix package: Add '--list-generations'.

* guix/scripts/package.scm: Import (srfi srfi-19).
  (generation-time, matching-generations): New functions.
  (show-help): Add '--list-generations'.
  (%options): Likewise.
  (guix-package)[process-query]: Add support for '--list-generations'.
* guix/ui.scm: Import (srfi srfi-19) and (ice-9 regex).
  (string->generations, string->duration): New functions.
* tests/guix-package.sh: Test '--list-generations'.
* tests/ui.scm: Import (srfi srfi-19).
  Test 'string->generations' and 'string->duration'.
* doc/guix.texi (Invoking guix-package): Document '--list-generations'.

derivations: 'derivation' and related procedures return a single value.

* guix/derivations.scm (derivation->output-path,
  derivation->output-paths): New procedures.
  (derivation-path->output-path): Use 'derivation->output-path'.
  (derivation-path->output-paths): Use 'derivation->output-paths'.
  (derivation): Accept 'derivation?' objects as inputs.  Return a single
  value.
  (build-derivations): New procedure.
  (compiled-modules): Use 'derivation->output-paths'.
  (build-expression->derivation)[source-path]: Add case for when the
  input matches 'derivation?'.
  [prologue]: Accept 'derivation?' objects in INPUTS.
  [mod-dir, go-dir]: Use 'derivation->output-path'.
* guix/download.scm (url-fetch): Adjust to the single-value return.
* guix/packages.scm (package-output): Use 'derivation->output-path'.
* guix/scripts/build.scm (guix-build): When the argument is
  'derivation-path?', pass it through 'read-derivation'.
  Use 'derivation-file-name' to print out the .drv file names, and to
  register them.  Use 'derivation->output-path' instead of
  'derivation-path->output-path'.
* guix/scripts/package.scm (roll-back): Adjust to the single-value
  return.
  (guix-package): Use 'derivation->output-path'.
* guix/ui.scm (show-what-to-build): Adjust to deal with 'derivation?'
  objects instead of .drv file names.
* gnu/system/grub.scm (grub-configuration-file): Use
  'derivation->output-path' instead of 'derivation-path->output-path'.
* gnu/system/vm.scm (qemu-image, system-qemu-image): Likewise.
* tests/builders.scm, tests/derivations.scm, tests/packages.scm,
  tests/store.scm, tests/union.scm: Adjust to the new calling
  convention.
* doc/guix.texi (Defining Packages, The Store, Derivations): Adjust
  accordingly.

tests: Clarify filtering of the "debug" output.

* tests/guix-package.sh: Clearly filter out the "debug" output of
  'gnu-make-boot0'.

derivations: Keep the .drv file name in <derivation> objects.

* guix/derivations.scm (<derivation>): Add 'file-name' field.
  (%read-derivation): Use (port-filename DRV-PORT) as the file name for
  the result.
  (derivation): Set the 'file-name' field in the result.
* tests/derivations.scm ("build derivation with 1 source"): Assert that
  'derivation-file-name' returns the right thing.

store: The 'references' parameter of 'add-text-to-store' is now optional.

* guix/store.scm (add-text-to-store): Make 'references' optional.
* tests/store.scm ("dead-paths", "references"): Use 'add-text-to-store'
  with no optional argument.
* doc/guix.texi (The Store): Adjust accordingly.

union: Don't traverse sub-directories only found in one element of the union.

This significantly reduces I/O when building profiles, especially with
lots of package-specific sub-directories (such as 'share/emacs/24.3',
'texmf', etc.)

* guix/build/union.scm (union-build)[file-tree](others-have-it?): New
  procedure.  Use it in the 'enter?' parameter of 'file-system-fold';
  change 'skip' parameter accordingly.
* tests/union.scm ("union-build"): Ensure that 'include' is a symlink
  and 'bin' is a directory.

derivations: Rename #:dependency-graphs to #:references-graphs.

* guix/derivations.scm (derivation, build-expression->derivation):
  Rename #:dependency-graphs to #:references-graphs, for consistency in
  the terminology.
* tests/derivations.scm: Adjust accordingly.

derivations: Add #:dependency-graphs to `build-expression->derivation'.

* guix/derivations.scm (build-expression->derivation): Add
  #:dependency-graphs keyword argument.  Pass it to `derivation'.
* tests/derivations.scm ("build-expression->derivation with
  #:dependency-graphs"): New test.
* doc/guix.texi (Derivations): Update `build-expression->derivation'
  description.

derivations: Add #:dependency-graphs `derivation' parameter.

* guix/derivations.scm (derivation): Add `dependency-graphs' keyword
  parameter; honor it.
* tests/derivations.scm (bootstrap-binary): New procedure.
  (%bash): Use it.
  (%mkdir): New variable.
  (directory-contents): Add `slurp' optional parameter.
  ("derivation with #:dependency-graphs"): New test.
* doc/guix.texi (Derivations): Update accordingly.

derivations: Move 3 positional parameters into keyword parameters.

* guix/derivations.scm (derivation): Turn `system', `env-vars', and
  `inputs' into keyword parameters.
  (build-expression->derivation): Adjust accordingly.
* gnu/packages/bootstrap.scm (%bootstrap-guile): Likewise.
* tests/derivations.scm, tests/store.scm: Likewise.
* doc/guix.texi (Derivations): Likewise.