gnu: system: file-systems: Add shared flag.

* gnu/build/file-systems.scm (mount-flags->bit-mask, mount-file-system):
Handle shared flag.
* gnu/system/file-systems.scm (invalid-file-system-flags): Add shared to known
flags.
* guix/build/syscalls.scm (MS_SHARED): New variable.
* doc/guix.texi (File Systems): Document shared flag.

channels: Consider news files as UTF-8-encoded by default.

Partly fixes <https://issues.guix.gnu.org/57039>.
Reported by Pierre-Henry Fröhring <contact@phfrohring.com>.

Previously, news file would be read using the current locale encoding.
This could lead to a test failure in 'tests/channels.scm' (in a test
that expects some Unicode-capable encoding) in case tests were run in a
non-Unicode locale.

* guix/channels.scm (channel-news-for-commit): Make port for NEWS-FILE
UTF-8 by default.

tests: git: Write files as UTF-8.

* guix/tests/git.scm (populate-git-repository): Add call to
'set-port-encoding!' in 'add' case.

channels: Add 'repository->guix-channel'.

* guix/channels.scm (repository->guix-channel): New procedure.
* guix/scripts/describe.scm (display-checkout-info): Use it instead of
the (git) interface, and adjust accordingly.

build-system/channel: Accept a channel or instance as the source.

* guix/build-system/channel.scm (latest-channel-instances*): New
variable.
(build-channels): New procedure, with code formerly in
'channel-build-system', augmented with clauses for when SOURCE is a
channel instance or a channel.
* doc/guix.texi (Build Systems): Adjust accordingly.

build-system: Add 'channel-build-system'.

* gnu/ci.scm (channel-build-system, channel-source->package): Remove.
* gnu/packages/package-management.scm (channel-source->package): New
procedure, moved from (gnu ci).
* guix/build-system/channel.scm: New file, with code moved from (gnu ci).
* doc/guix.texi (Build Systems): Document it.

read-print: Add 'case' and 'cond' special forms.

* guix/read-print.scm (%special-forms): Add 'case' and 'cond'.
* tests/read-print.scm: Add tests.

read-print: Support printing multi-line comments.

* guix/read-print.scm (%not-newline): New variable.
(print-multi-line-comment): New procedure.
(pretty-print-with-comments): Use it.
* tests/read-print.scm ("pretty-print-with-comments, multi-line
comment"): New test.

style: Add '--whole-file' option.

* guix/scripts/style.scm (format-whole-file): New procedure.
(%options, show-help): Add '--whole-file'.
(guix-style): Honor it.
* tests/guix-style.sh: New file.
* Makefile.am (SH_TESTS): Add it.
* doc/guix.texi (Invoking guix style): Document it.

read-print: 'canonicalize-comment' leaves top-level comments unchanged.

This lets users use three leading semicolons, for instance, in top-level
comments.

* guix/read-print.scm (canonicalize-comment): Add INDENT parameter and
honor it.
(pretty-print-with-comments): Change default value of #:format-comment.
Call FORMAT-COMMENT with INDENT as the second argument.
* tests/read-print.scm: Adjust test accordingly.

read-print: Add code to read and write sequences of expressions/blanks.

* guix/read-print.scm (read-with-comments): Add #:blank-line? and honor it.
(read-with-comments/sequence, pretty-print-with-comments/splice): New
procedures.
* tests/read-print.scm (test-pretty-print/sequence): New macro.
Add tests using it.

read-print: Recognize page breaks.

* guix/read-print.scm (<page-break>, page-break?, page-break)
(char-set:whitespace-sans-page-break): New variables.
(space?): New procedure.
(read-vertical-space): Use it.
(read-until-end-of-line): New procedure.
(read-with-comments): Add #\page case.
(pretty-print-with-comments): Add 'page-break?' case.
* tests/read-print.scm ("read-with-comments: top-level page break"): New
test.
Add round-trip test with page break within an sexp.

read-print: Read and render vertical space.

* guix/read-print.scm (<vertical-space>, vertical-space?)
(vertical-space, vertical-space-height): New variables.
(combine-vertical-space, canonicalize-vertical-space)
(read-vertical-space): New procedures.
(read-with-comments): Use it in the #\newline case.
(pretty-print-with-comments): Add #:format-vertical-space and honor it.
Add case for 'vertical-space?'.
* guix/scripts/style.scm (format-package-definition): Pass
 #:format-vertical-space to 'object->string*'.
* tests/read-print.scm ("read-with-comments: list with blank line")
("read-with-comments: list with multiple blank lines")
("read-with-comments: top-level blank lines")
("pretty-print-with-comments, canonicalize-vertical-space"): New tests.
Add a couple of additional round-trip tests.

read-print: Introduce <blank> parent class of <comment>.

* guix/read-print.scm (<blank>, blank?): New record type.
(<comment>): Redefine using the record interface.
(read-with-comments, pretty-print-with-comments): Change some uses of
'comment?' to 'blank?'.
* guix/scripts/style.scm (simplify-inputs)[simplify-expressions]: Use
'blank?' instead of 'comment?'.

read-print: Expose comment constructor.

* guix/read-print.scm (<comment>): Rename constructor to
'string->comment'.
(comment): New procedure.
(read-with-comments, canonicalize-comment): Use 'string->comment'
instead of 'comment'.

read-print: Add System and Home special forms.

* guix/read-print.scm (%special-forms): Add System and Home forms.
(%newline-forms): Add 'services'.

style: Move reader and printer to (guix read-print).

* guix/scripts/style.scm (<comment>, read-with-comments)
(vhashq, %special-forms, %newline-forms, prefix?)
(special-form-lead, newline-form?, escaped-string)
(string-width, canonicalize-comment, pretty-print-with-comments)
(object->string*): Move to...
* guix/read-print.scm: ... here.  New file.
* guix/scripts/import.scm: Adjust accordingly.
* tests/style.scm: Move 'test-pretty-print' and tests to...
* tests/read-print.scm: ... here.  New file.
* Makefile.am (MODULES): Add 'guix/read-print.scm'.
(SCM_TESTS): Add 'tests/read-print.scm'.

lint: Add '-e'.

* guix/scripts/lint.scm (show-help, %options): Add '-e'.
(guix-lint): Call 'specification->package' while traversing OPTS.  Add
case for 'expression pair.  Adjust 'for-each' loop to expect packages.
* doc/guix.texi (Invoking guix lint): Document it.

build-system/perl: Support cross-compilation of some Perl packages.

* guix/build-system/perl.scm: Add info on cross-compilation.
(lower)[private-keywords]: Remove #:target when cross-compiling.
(lower)[target]: Set.
(host-inputs)[perl]: New entry.
(host-inputs)[(standard-packages)]: Move to ...
(build-inputs)[(standard-packages)]: ... here when cross-compiling.
(build-inputs)[standard-cross-packages]: Add when cross-compiling.
(target-inputs): New entry when cross-compiling.
(build): Use perl-cross-build when cross-compiling.
(perl-cross-build): New procedure.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

guix system: Remove unused 'read-operating-system' procedure.

* guix/scripts/system.scm (read-operating-system): Remove.
* gnu/ci.scm: Remove unused (guix scripts system) import.