Add the `valid-path?' RPC.

* guix/store.scm (valid-path?): New procedure.

* tests/builders.scm ("http-fetch", "gnu-build"): Use it.
* tests/derivations.scm ("add-to-store, flat", "add-to-store,
  recursive", "derivation with no inputs", "build derivation with 1
  source", "build derivation with coreutils",
  "build-expression->derivation with expression returning #f"):
  Likewise.

Add missing `set-build-options' parameters.

* guix/store.scm (set-build-options)[build-cores, use-substitutes?]: New
  keyword parameters.
  [send]: Change to expect a type, and use `write-arg'.
  Send settings for BUILD-CORES and USE-SUBSTITUTES? when the server
  supports it.

Add (distro) with a package searching facility.

* Makefile.am (MODULES): Add `distro.scm'.

* distro.scm: New file.
* po/POTFILES.in: Add it.

* tests/packages.scm ("find-packages-by-name", "find-packages-by-name
  with version"): New tests.

Add a libgcrypt-based implementation of `sha256'.

* guix/utils.scm (sha256): Add a libgcrypt-based implementation using
  the FFI.

Gettextize, with GNU Gettext 0.18.1.

* Makefile.am (EXTRA_DIST): Add `build-aux/config.rpath'.
  (SUBDIRS, ACLOCAL_AMFLAGS): New variables.

* configure.ac: Use `AM_GNU_GETTEXT'.  Emit `po/Makefile.in'.

* po/Makevars, po/POTFILES.in: New files.

distro: Add libsigsegv and GNU Awk.

* guix/packages.scm (<package>)[arguments]: Default to '().

* distro/base.scm (libsigsegv, gawk): New packages.
  (hello): Use GAWK instead of (nixpkgs-derivation "gawk").

derivation: Remove duplicate inputs.

* guix/derivations.scm (derivation): Remove duplicates from INPUT.

build-system/gnu: Add GNU Awk to the standard inputs.

* guix/build-system/gnu.scm (%standard-inputs): Add GNU Awk.

packages: Add a `home-page' field.

* guix/packages.scm (<package>)[home-page]: New field.

* distro/base.scm (hello)[home-page]: Initialize.

Track the source location of packages.

* guix/packages.scm (<location>): New record type.
  (location, source-properties->location): New procedures.
  (<package>)[location]: New field.

* tests/packages.scm ("GNU Hello"): Test `package-location'.

Add a sha256 fallback that uses Coreutils instead of libchop.

* guix/utils.scm (compile-time-value): Move to the top.
  (sha256): Add an implementation that uses Coreutils, for when libchop
  is unavailable.

Introduce `compile-time-value' and use it.

* guix/utils.scm (compile-time-value): New macro.
  (%nixpkgs-directory): Use it.

* guix/build-system/gnu.scm (%standard-inputs): Likewise.

Add a declarative packaging layer.

* Makefile.am (MODULES): Add `guix/packages.scm' and `distro/base.scm'.
  (TESTS): Add `tests/packages.scm'.
  (EXTRA_DIST): New variable.

* guix/packages.scm, distro/base.scm, tests/packages.scm: New files.

* guix/http.scm (http-fetch): Make `name' an optional argument, to match
  the expectations of `package-source-derivation'.

build-system/gnu: Have `configure-flags' and `make-flags' evaluated.

* guix/build-system/gnu.scm (gnu-build): Double-quote the default value
  of MAKE-FLAGS and CONFIGURE-FLAGS.  Don't quote them in BUILDER.

build: Define $NIXPKGS when compiling.

* Makefile.am (.scm.go): Define $NIXPKGS.

Abstract build systems.

* Makefile.am (MODULES): Add `guix/build-system.scm' and
  `guix/build-system/gnu.scm'.  Remove `guix/gnu-build-system.scm'.

* guix/build-system.scm: New file.
* guix/gnu-build-system.scm: Rename to...
* guix/build-system/gnu.scm: ... this.
  (gnu-build-system): New variable.

* tests/builders.scm: Adjust `use-module' clauses.
  ("gnu-build-system"): New test.

Add `define-record-type*'.

* guix/utils.scm (define-record-type*): New macro.

* tests/utils.scm ("define-record-type*"): New test.

build-expression->derivation: Move module forms at the top-level.

* guix/derivations.scm (build-expression->derivation)[module-form?]: New
  procedure.
  [prologue]: Add any form of EXP that matches MODULE-FORM?.
  [builder]: Remove any MODULE-FORM? from EXP.

gnu-build-system: Structure as a customizable sequence of phases.

* guix/build/gnu-build-system.scm (set-paths, build, check, install):
  New procedures.
  (unpack): Make `source' a keyword arg; add `#:allow-other-keys'.
  (configure): Likewise.
  (%standard-phases): New variable.
  (gnu-build): Make `source', `outputs', and `inputs' keyword arguments;
  add `phases' keyword argument; #:allow-other-keys; add rest arguments
  `args'.  Invoke each of PHASES in order within `every'.

* guix/gnu-build-system.scm (gnu-build): Add `make-flags' and `phases'
  keyword arguments.  Update builder's `gnu-build' call to match the new
  convention.

gnu-build-system: Add GNU Diffutils and GNU Path to the standard inputs.

* guix/gnu-build-system.scm (%standard-inputs): Add Diffutils and Patch.