tests: Remove extraneous test.

* tests/derivations.scm ("build-expression->derivation for fixed-output
  derivation"): Remove test.  It is redundant with that in builders.scm,
  and doesn't work out of the box with the statically-linked
  %BOOTSTRAP-GUILE.

Move base32 code to (guix base32).

* guix/utils.scm (bytevector-quintet-ref, bytevector-quintet-ref-right,
  bytevector-quintet-length, bytevector-quintet-fold,
  bytevector-quintet-fold-right, make-bytevector->base32-string,
  %nix-base32-chars, %rfc4648-base32-chars, bytevector->base32-string,
  bytevector->nix-base32-string, bytevector-quintet-set!,
  bytevector-quintet-set-right!, base32-string-unfold,
  base32-string-unfold-right, make-base32-string->bytevector,
  base32-string->bytevector, nix-base32-string->bytevector): Move to...
* guix/base32.scm: ... here.  New file.

* tests/utils.scm (%nix-hash, "bytevector->base32-string",
  "base32-string->bytevector", "nix-base32-string->bytevector", "sha256
  & bytevector->base32-string"): Move to...
* tests/base32.scm: ... here.  New file

* guix-download.in, guix/derivations.scm, guix/packages.scm,
  guix/snix.scm, tests/builders.scm, tests/derivations.scm: Adjust
  accordingly.
* guix.scm (%public-modules): Add `base32'.

derivations: build-expression->derivation: Builder only refers to sources.

* guix/derivations.scm (build-expression->derivation)[source-path]: New
  procedure.
  [builder]: Pass only sources as references.  This fixes a bug whereby
  changing a fixed-output drv referred to by a builder would cause the
  builder's hash to change, thereby leading to a full rebuild.
* tests/derivations.scm ("build-expression->derivation with a
  fixed-output input"): New test.

derivations: Add tests relative to fixed-output derivations.

* tests/derivations.scm ("fixed-output derivation"): Add comment that
  the reference to BUILDER is optional.
  ("fixed-output derivation: output paths are equal",
  "derivation with a fixed-output input",
  "build-expression->derivation: same fixed-output path"): New tests.

distro: Move bootstrap packages to (distro packages bootstrap).

* distro/packages/base.scm (glibc-dynamic-linker, %bootstrap-guile,
  bootstrap-origin, package-from-tarball, %bootstrap-base-url,
  %bootstrap-coreutils&co, %bootstrap-binutils, %bootstrap-glibc,
  %bootstrap-gcc, %bootstrap-inputs, package-with-bootstrap-guile): Move
  to ...
* distro/packages/bootstrap.scm: ... here.  New file.
* Makefile.am (MODULES): Add it.
* tests/builders.scm: Use (distro packages bootstrap).
  (%bootstrap-guile): Remove.
* tests/packages.scm: Likewise.
* tests/union.scm: Likewise, and remove @@ to access %bootstrap-inputs.
* tests/derivations.scm: Use (distro packages bootstrap) and remove @@
  to access %bootstrap-coreutils&co.
* HACKING (When the platform is supported by Nixpkgs): Update
  accordingly.

tests: Run without substitutes.

* tests/builders.scm, tests/derivations.scm, tests/packages.scm: Set
  #:use-substitutes? #f for %STORE.

tests: Use our own bootstrap tools.

* tests/builders.scm (%bootstrap-inputs): Use %BOOT0-INPUTS from the distro.
* tests/packages.scm (%bootstrap-inputs): Likewise.
* tests/derivations.scm (%coreutils): Alias for %BOOTSTRAP-COREUTILS&CO.

derivations: Pass the derivation of guile-for-build to `imported-files' & co.

* guix/derivations.scm (%guile-for-build): Initialize to #f.
  (imported-files, imported-modules, compiled-modules): Add `guile'
  keyword parameter.  Pass it down to `build-expression->derivation'.
  (build-expression->derivation)[guile-drv]: New variable.  Pass it as
  the #:guile parameter for `imported-modules' and `compiled-modules'.

* tests/derivations.scm: Set %GUILE-FOR-BUILD to the derivation of
  %BOOTSTRAP-GUILE.

store: Add `query-path-hash'.

* guix/store.scm (write-arg, read-arg): Add `base16' literal and
  corresponding rule.
  (query-path-hash): New operation.

* tests/derivations.scm ("fixed-output derivation"): Check whether
  `query-path-hash' returns a bytevector.

derivations: Compile the #:modules passed to `build-expression->derivation'.

* guix/derivations.scm (imported-files)[parent-dirs]: Move to...
  (parent-directories): ... here.  New procedure.
  (compiled-modules): New procedure.
  (build-expression->derivation): Use it.

* tests/derivations.scm ("build-expression->derivation with modules"):
  New test.

derivation: Coalesce multiple occurrences of the same input.

* guix/derivations.scm (write-derivation)[coalesce-duplicate-inputs]:
  New procedure.
  Use it to process INPUTS.

* tests/derivations.scm ("user of multiple-output derivation"): New
  test.

Fix `derivation-hash' for outputs not sorted alphabetically.

* guix/derivations.scm (derivation-hash): Reorder OUTPUTS.
* tests/derivations.scm ("multiple-output derivation, non-alphabetic
  order"): New test.

Add `derivation-prerequisites' and `derivation-prerequisites-to-build'.

* guix/derivations.scm (derivation-prerequisites,
  derivation-prerequisites-to-build): New procedures.

* tests/derivations.scm ("build-expression->derivation and
  derivation-prerequisites", "build-expression->derivation and
  derivation-prerequisites-to-build"): New tests.

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.

build-expression->derivation: Have the build fail when EXP returns #f.

* guix/derivations.scm (build-expression->derivation)[builder]: Pass the
  result of EXP to `exit'.

* tests/derivations.scm ("build-expression->derivation with expression
  returning #f"): New test.

Change `build-expression->derivation' to support sub-derivation inputs.

* guix/derivations.scm (build-expression->derivation): Change to expect
  INPUTS to have the form (NAME DRV-PATH SUB-DRV) or (NAME DRV-PATH),
  instead of (NAME . DRV-PATH).  Update callers accordingly.

* guix/gnu-build-system.scm, tests/builders.scm, tests/derivations.scm:
  Update accordingly.

Fix `imported-files' for files with a common prefix.

* guix/derivations.scm (imported-files)[builder]: For TAIL, check
  whether it exists before (mkdir TAIL).

* tests/derivations.scm ("imported-files"): Add file with a common
  prefix.

Add `add-to-store' test for flat files.

* tests/derivations.scm ("add-to-store, flat"): New test.

Add `imported-files'.

* guix/derivations.scm (imported-files): New procedure.
  (build-expression->derivation): Correctly handle inputs that are
  sources and not derivation paths.

* tests/derivations.scm ("imported-files"): New test.

Fix the `build-expression->derivation' fixed-output test.

* tests/derivations.scm ("build-expression->derivation"): Fix the
  builder to actually pass a bytevector to `put-bytevector'.