guix build: '--with-source' overrides the 'replacement' of a package.

* guix/scripts/build.scm (package-with-source): Set 'replacement' to #f.
* tests/scripts-build.scm ("options->transformation, with-source,
replacement"): New test.

environment: Add '--root' option.

* guix/scripts/environment.scm (show-help, %options): Add --root.
(register-gc-root): New procedure.
(guix-environment): Call 'register-gc-root' when OPTS has a 'gc-root'
option.
* doc/guix.texi (Invoking guix environment): Document it.
* tests/guix-environment.sh: Add tests.

guix import: Print list of expressions.

* guix/scripts/import.scm (guix-import): Print list of expressions.

import cran: Add "recursive" option.

* guix/scripts/import/cran.scm: (%options): Add "recursive" option.
(guix-import-cran): Handle "recursive" option.
* doc/guix.texi (Invoking guix import): Document it.

profiles: Remove dependency on 'glibc-utf8-locales' for tests.

Commit 1af0860e8be81c01ad405c1226d6bc4516e62863 added a mandatory
dependency on 'glibc-utf8-locales', which entails long rebuilds for
tests.

* guix/profiles.scm (profile-derivation): Add #:locales? parameter.
Add 'set-utf8-locale' variable.  Use it when LOCALES? is true.
(link-to-empty-profile): Pass #:locales? #f.
* guix/scripts/environment.scm (inputs->profile-derivation): Pass
  #:locales?.
* guix/scripts/package.scm (build-and-use-profile): Likewise.
* tests/packages.scm ("--search-paths with pattern"): Pass #:locales? #f.
* tests/profiles.scm ("profile-derivation")
("profile-derivation, inputs", "profile-manifest, search-paths")
("etc/profile", "etc/profile when etc/ already exists"):
("etc/profile when etc/ is a symlink"): Likewise.

refresh: Make dependency on (guix import crates) weak.

Reported by Tobias Geerinckx-Rice <me@tobias.gr>.

* guix/scripts/refresh.scm: Do not explicitly import (guix import crates).

graph: Add "list-backend" and "backend" options.

* guix/graph.scm (%graph-backends): New variable.
* guix/scripts/graph.scm (lookup-backend, list-backends): New
procedures.
(%options): Add options for "backend" and "list-backends".
(show-help): Add help texts for "backend" and "list-backend" options.
(%default-options): Add "backend" default.
(guix-graph): Pass backend argument to "export-graph".
* doc/guix.texi (Invoking guix graph): Document the new options.

import: Add updater for rust crates.

* guix/import/crate.scm (crate-package?, latest-release,
  %crate-updater): New variables.
* guix/scripts/refresh.scm (%updaters): Add crate updater.
* doc/guix.texi: Add crate updater to table.

import: Add importer for rust crates.

* guix/import/crate.scm: New file.
* guix/scripts/import/crate.scm: New file.
* guix/scripts/import.scm (importers): Add crate importer.
* tests/crate.scm: New file.
* doc/guix.texi: Add crate importer to table.
* Makefile.am (MODULES, SCM_TESTS): Add files.

import: cpan: Add updater.

* guix/import/cpan.scm (module->dist-name): Fetch the field of interest.
(cpan-fetch): Accept release name rather than module name.
(fix-source-url): Rename to ...
(cpan-source-url): ... this.  Take metadata as parameter.
(package->upstream-name, cpan-version, cpan-package?, latest-release):
New procedures.
(cpan-module->sexp): Use cpan-version and cpan-source-url.
(%cpan-updater): New variable.
* guix/scripts/refresh.scm (%updaters): Add %CPAN-UPDATER.

Merge branch 'master' into staging

offload: Allow testing machines that match a regexp.

* guix/scripts/offload.scm (check-machine-availability): Add 'pred'
parameter and honor it.
(guix-offload): for the "test" sub-command, accept an extra 'regexp'
parameter.  Pass a second argument to 'check-machine-availability'.

offload: Test each machine only once.

* guix/scripts/offload.scm (check-machine-availability)[build-machine=?]:
New procedure.
Add call to 'delete-duplicates'.

offload: Do not read ~/.ssh/known_hosts.

* guix/scripts/offload.scm (open-ssh-session): Pass #:knownhosts to
'make-session'.

Merge remote-tracking branch 'origin/master' into staging

offload: Increase the connection timeout.

* guix/scripts/offload.scm (open-ssh-session): Set #:timeout to 10.

offload: Send the build log to the right file descriptor.

This fixes a regression introduced in
21531add3205e400707c8fbfd841845f9a71863a whereby the build log would no
longer be sent to FD 4, thereby leading the daemon to not see the build
log.

* guix/scripts/offload.scm (transfer-and-offload): Parameterize
CURRENT-BUILD-OUTPUT-PORT.

offload: Fix plural of some messages.

* guix/scripts/offload.scm (send-files): Use 'N_' for possibly plural
message.  Write "store item" instead of "store file".
(retrieve-files): Likewise.

offload: Make the compression methods configurable.

* guix/scripts/offload.scm (<build-machine>)[compression]
[compression-level]: New fields.
(open-ssh-session): Honor them.
* doc/guix.texi (Daemon Offload Setup): Document them.

guix system: If the new system generation already exists, overwrite it.

Fixes <http://bugs.gnu.org/25100>.

Before that, 'guix system reconfigure' would fail if the next generation
already existed.

* guix/scripts/system.scm (switch-to-system): Use 'switch-symlink'
instead of 'symlink'.
* doc/guix.texi (Using the Configuration System, Invoking guix system):
Document the behavior.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>