* 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.
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.
* guix/build/union.scm (union-build): Prepend "." to the result of
`union-tree', to match the expectations of `delete-duplicate-leaves'.
Don't do mkdir when SUBDIR is ".".
* tests/union.scm ("union-build"): Keep duplicates in %BOOTSTRAP-INPUTS.
* guix/build/union.scm (delete-duplicate-leaves): New procedure.
(union-build)[leaf=?, resolve-collision]: New procedures.
Use `delete-duplicate-leaves' on the result of `tree-union'.
* tests/union.scm ("delete-duplicate-leaves, default",
"delete-duplicate-leaves, file names"): New tests.
* tests/derivations.scm (%bash): New variable.
Replace occurrences of "/bin/sh" by %BASH.
* tests/union.scm ("union-build"): Delete duplicates from
%BOOTSTRAP-INPUTS.
* tests/builders.scm (network-reachable?): New variable.
("url-fetch", "gnu-build"): Skip unless NETWORK-REACHABLE?.
* tests/derivations.scm (%coreutils): Check for network access.
("build-expression->derivation with one input"): Skip when %COREUTILS
is #f.
* tests/guix-package.sh: Skip installation of GNU Make when the network
is unreachable.
* tests/packages.scm ("GNU Make, bootstrap"): Likewise.
* tests/union.scm ("union-build"): Likewise.
