guix package: Specify inputs for each manifest entry.

* guix/scripts/package.scm (<manifest-entry>): Add 'inputs' field.
  (manifest=?, lower-input): New procedure.
  (profile-derivation)[builder]: Add #:log-port argument to
  'union-build'.
  [ensure-valid-input]: Remove.
  Add each entry's inputs to the input list.
  (options->installable): Return just the list of entries.
  [package->manifest-entry]: Set 'inputs' field.
  [canonicalize-deps]: Rename to...
  [deduplicate]: ... this.  Remove input fiddling.
  (guix-package)[process-actions]: Use 'manifest=?' to compare the new
  and old manifests.  Pass directly PROF-DRV to 'show-what-to-build'.
  Pass #:print-build-trace #f to 'set-build-options'.

guix package: Always use the term "profile", not "user environment".

* guix/scripts/package.scm (%user-environment-directory): Rename to...
  (%user-profile-directory): ... this.  Update users accordingly.
  (profile-derivation): Use the term "profile" instead of "user
  environment", and use "profile" as the derivation name.

guix package: Introduce <manifest> and <manifest-entry> types.

* guix/scripts/package.scm (<manifest>, <manifest-entry>): New record
  types.
  (make-manifest, read-manifest, manifest->sexp, sexp->manifest,
  read-manifest, write-manifest, remove-manifest-entry, manifest-remove,
  manifest-installed?): New procedures.
  (profile-derivation): Take a manifest as the second parameter.  Use
  'manifest->sexp'.  Expect <manifest-entry> objects instead of
  "tuples".  Adjust callers accordingly.
  (search-path-environment-variables): Changes 'packages' parameter to
  'entries'.  Rename 'package-in-manifest->package' to
  'manifest-entry->package'; expect <manifest-entry> objects.
  (display-search-paths): Rename 'packages' to 'entries'.
  (options->installable): Change 'installed' to 'manifest'.  Have
  'canonicalize-deps' return name/path tuples instead of raw packages.
  Rename 'package->tuple' to 'package->manifest-entry'.  Use
  <manifest-entry> objects instead of tuples.
  (guix-package)[process-actions]: Likewise.  Rename 'packages' to
  'entries'.
  [process-query]: Use 'manifest-entries' instead of
  'manifest-packages'.

guix package: Better separate option processing.

* guix/scripts/package.scm (find-package): Rename to...
  (specification->package+output): ... this.  Rename 'name' parmameter
  to 'spec'.  Return a package and output name instead of a tuple.
  (options->installable): New procedure
  (guix-package)[process-actions]: Use it, and remove corresponding
  code.

guix package: Declutter the entry point.

* guix/scripts/package.scm (newest-available-packages,
  find-best-packages-by-name, find-package, upgradeable?): New
  procedures, moved from...
  (guix-package): ... here.

guix package: '--search' matches against package names.

* guix/scripts/package.scm (find-packages-by-description): Return
  packages whose name matches RX.

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'.

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: Add 'link-to-empty-profile'.

* guix/scripts/package.scm (link-to-empty-profile): New function.
  (roll-back): Use it.

guix package: Exit with 0 when there is nothing to list.

* guix/scripts/package.scm (guix-package)[process-query]: Exit with 0
  when there are no generations containing packages or no profiles.

Merge branch 'master' into core-updates

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.

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.

Merge branch 'master' into core-updates

guix package: Show most recently installed packages last.

Suggested by Andreas Enge <andreas@enge.fr>.

* guix/scripts/package.scm (guix-package)[list-generations,
  list-installed]: Reverse the result of 'manifest-packages'.
* doc/guix.texi (Invoking guix package): Document the order of packages
  for '--list-generations' and '--list-installed'.

guix package: Sort the list of generation numbers in '--list-generations'.

* guix/scripts/package.scm (generation-numbers): Sort the result.

guix package: Internationalize "Generation" string.

* guix/scripts/package.scm (guix-package): Internationalize generation
  listing.

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.