services: Service types can now specify a default value for instances.

* gnu/services.scm (&no-default-value): New variable.
(<service-type>)[default-value]: New field.
(<service>): Rename constructor from 'service' to 'make-service'.
(service): New macro.
(%service-with-default-value): New procedure.
(&missing-value-service-error): New error condition.
* tests/services.scm ("services, default value"): New test.
* doc/guix.texi (Service Types and Services): Document 'default-value'.
(Service Reference): Explain default values.

services: 'service-parameters' becomes 'service-value'.

* gnu/services.scm (<service>)[parameters]: Rename to...
[value]: ... this.
Change calls to 'service-parameters' to 'service-value'.
* gnu/system.scm, gnu/tests/base.scm,
guix/scripts/system.scm, tests/services.scm: Likewise.
* doc/guix.texi (Service Reference): Adjust accordingly.

size: Add test to multiple 'store-profile' arguments.

* tests/size.scm ("store-profile with multiple items"): New test.

packages: Add 'package-mapping' and base 'package-input-rewriting' on it.

* guix/packages.scm (package-mapping): New procedure.
(package-input-rewriting): Rewrite in terms of 'package-mapping'.
* tests/packages.scm ("package-mapping"): New test.
* doc/guix.texi (Defining Packages): Document it.

tests: Adjust search-paths test following the introduction of aarch64.

Fixes a regression introduced in
3b88f3767d9f3ad2cc64173525cd53d429bfe7e7.

* tests/search-paths.scm ("evaluate-search-paths, separator is #f"):
Change the expected result to "aarch64-linux".

packages: Catch invalid input errors for structs.

Reported by Thomas Sigurdsen <thomas.sigurdsen@gmail.com>
at <https://lists.gnu.org/archive/html/help-guix/2017-04/msg00007.html>.

* guix/packages.scm (expand-input): Add 'guard' form around call to
'package-source-derivation'.
* tests/packages.scm (dummy): New test.

gexp: 'lower-object' raises an exception when passed an invalid object.

* guix/gexp.scm (&gexp-error, &gexp-input-error): New error conditions.
(lower-object): Raise &gexp-input-error when 'lookup-compiler' returns #f.
* tests/gexp.scm ("lower-object & gexp-input-error?"): New test.
* guix/ui.scm (call-with-error-handling): Add case for 'gexp-input-error?'.

Merge branch 'core-updates'

Merge branch 'master' into core-updates

Most conflicts are from 6fd52309b8f52c9bb59fccffac53e029ce94b698.

derivations: Do not fetch narinfos for non-substitutable items.

This avoids connections to substitute servers for derivations that are
not substitutable anyway, such as profiles.

Reported by Andy Wingo.

* guix/derivations.scm (substitution-oracle): Skip derivations that do
not pass 'substitutable-derivation?'.
* tests/derivations.scm ("substitution-oracle and #:substitute? #f"):
New test.

Merge branch 'master' into core-updates

ui: Support Texinfo markup in package synopses.

* guix/ui.scm (package-field-string): New procedure.
(package-description-string): Use it.
(package-synopsis-string): New procedure.
(package->recutils): Use it.
* guix/scripts/lint.scm (check-synopsis-style)[check-texinfo-markup]:
New procedure.  Use it in checks.
* tests/lint.scm: Test it.
* gnu/packages/perl.scm (perl-try-tiny)[synopsis]: Adjust for the
Texinfo markup.

union: Add create-all-directories? parameter to 'union-build'.

* guix/build/union.scm (union-build): Add create-all-directories? keyword
parameter.
* tests/union.scm ("union-build #:create-all-directories? #t"): New test.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

Merge remote-tracking branch 'origin/master' into core-updates

tests: Skip 'guix pack' test when networking is unavailable.

* tests/pack.scm ("self-contained-tarball"): Skip unless (network-reachable?).

tests: Fix 'cond-expand' clause for 2.2/2.0.

Fixes a mistake in a9a0227c0127e1813190a7664f7ad858e791480d.

* tests/store.scm ("current-build-output-port, UTF-8 + garbage"):
Inverse the 'cond-expand' clauses since the 'guile-2.0' feature doesn't
exist.

publish: Make the nar URL prefix a parameter.

* guix/scripts/publish.scm (narinfo-string): Add #:nar-path and honor it.
(render-narinfo): Likewise.
(make-request-handler): Likewise.
(run-publish-server): Likewise.
* tests/publish.scm ("custom nar path"): New test.

publish: The public and private keys are now SRFI-39 parameters.

* guix/scripts/publish.scm (%default-options): Add 'public-key-file' and
'private-key-file'.
(lazy-read-file-sexp): Remove.
(%private-key, %public-key): Turn into SRFI-39 parameters.
(signed-string, render-narinfo): Adjust accordingly.
(guix-publish): Honor 'public-key-file' and 'private-key-file' from
OPTS.  Use 'parameterize'.
* guix/pk-crypto.scm (read-file-sexp): New procedure.
* tests/publish.scm: Initialize '%public-key' and '%private-key'.

Merge remote-tracking branch 'origin/master' into core-updates

file-systems: Do not use (gnu packages …).

Fixes a regression introduced in
7208995426714c9fc3ad59cadc3cc0f52df0f018 whereby (gnu system
file-systems) would pull in (gnu packages …) module, which in turn
breaks when importing things like (gnu build shepherd).

* gnu/system/file-systems.scm (file-system-type-predicate): Export.
(file-system-packages): Move to...
* gnu/system/linux-initrd.scm (file-system-packages): ... here.  Add
docstring.
* gnu/services/base.scm: Use it.
* tests/file-systems.scm ("does not pull (gnu packages …)"): New test.