This new backend allows gnus to handle arbitrary sets of messages
spanning multiple groups, even when these groups are from different
backends and different servers. All gnus glue is removed from
nnir (leaving only the backend search functions) and gnus
search-related processing is done through nnselect. In appropriate
places 'nnir' has been replaced by 'nnselect' or 'search'.

* etc/NEWS: Document the change.
* doc/misc/gnus.texi: New  documentation for nnselect and update
searching and thread-referral  sections.
* lisp/gnus/nnselect.el: New file.
* lisp/gnus/nnir.el: Remove all gnus glue, leaving only searching
capability. Improve documentation strings.
* lisp/gnus/gnus-group.el (gnus-group-read-ephemeral-search-group,
gnus-group-make-search-group): New functions.
* lisp/gnus/gnus-msg.el (gnus-setup-message, gnus-group-news,
gnus-summary-news-other-window): Update to work for nnselect. Fix
gnus-newsgroup-name wrangling.
*lisp/gnus/gnus-registry.el
(gnus-registry-action,gnus-registry-ignore-group-p): Make work from nnselect.
* lisp/gnus/nnheader.el (nnheader-parse-head, nnheader-parse-nov):
Rework and consolidate header parsing.
* lisp/gnus/gnus-agent.el (gnus-agent-regenerate-group):
* lisp/gnus/gnus-cache.el (gnus-possibly-enter-article):
* lisp/gnus/gnus-cloud.el (gnus-cloud-available-chunks):
* lisp/gnus/gnus-msg.el (gnus-inews-yank-articles):
* lisp/gnus/gnus-sum. (gnus-get-newsgroup-headers):
* lisp/gnus/nndiary.el (nndiary-parse-head):
* lisp/gnus/nnfolder.el (nnfolder-parse-head):
* lisp/gnus/nnmaildir.el (nnmaildir--update-nov):
* lisp/gnus/nnml.el (nnml-parse-head):
* lisp/gnus/nnspool.el (nnspool-insert-nov-head):
Use new header parsing.
* lisp/gnus/gnus-start.el (gnus-read-active-for-groups): Rescan on
activation by default.
* lisp/gnus/gnus-sum.el (gnus-summary-line-format-alist): New specs
for virtual groups.
(gnus-article-sort-by-rsv, gnus-thread-sort-by-rsv):  New functions to
allow sorting by search RSV.

nnmail-cache-close did not work when ~/.nnmail-cache was a symlink
to some other directory.  Reported by Michael Albinus (Bug#39793).
* lisp/gnus/nnbabyl.el (nnbabyl-create-mbox):
* lisp/gnus/nndiary.el (nndiary-generate-nov-file):
* lisp/gnus/nnfolder.el (nnfolder-possibly-change-group):
* lisp/gnus/nnmbox.el (nnmbox-create-mbox):
* lisp/gnus/nnml.el (nnml-generate-nov-file):
Pass ‘excl’ to nnmail-write-region when creating a file, for safety.
* lisp/gnus/nnmail.el (nnmail-write-region):
Add optional MUSTBENEW arg, to stay consistent with write-region.
Past ‘nofollow’ to set-file-modes only when MUSTBENEW is ‘excl’.

* lisp/gnus/gnus-agent.el (gnus-agent-synchronize-flags-server):
Use `gnus-get-buffer-create' instead of `get-buffer-create'
* lisp/gnus/gnus-bookmark.el (gnus-bookmark-write-file): Likewise.
(gnus-bookmark-bmenu-list): Likewise.
(gnus-bookmark-show-details): Likewise.
* lisp/gnus/gnus-draft.el (gnus-draft-setup): Likewise.
* lisp/gnus/gnus-icalendar.el (gnus-icalendar-reply): Likewise.
* lisp/gnus/gnus-int.el (gnus-backend-trace): Likewise.
* lisp/gnus/gnus-srvr.el (gnus-enter-server-buffer): Likewise.
* lisp/gnus/gnus-sum.el (gnus-summary-pipe-output): Likewise.
* lisp/gnus/gnus-util.el (gnus-output-to-rmail): Likewise.
(gnus-output-to-mail): Likewise.
(gnus-multiple-choice): Likewise.
* lisp/gnus/mail-source.el (mail-source-call-script): Likewise.
* lisp/gnus/message.el (message-cancel-news): Likewise.
(message-resend): Likewise.
* lisp/gnus/mm-archive.el (mm-dissect-archive): Likewise.
* lisp/gnus/mml1991.el (mml1991-mailcrypt-sign): Likewise.
(mml1991-mailcrypt-encrypt): Likewise.
* lisp/gnus/mml2015.el (mml2015-mailcrypt-verify): Likewise.
(mml2015-mailcrypt-clear-verify): Likewise.
* lisp/gnus/nnbabyl.el (nnbabyl-request-move-article): Likewise.
* lisp/gnus/nndiary.el (nndiary-request-move-article): Likewise.
(nndiary-find-group-number): Likewise.
(nndiary-open-nov): Likewise.
(nndiary-generate-nov-file): Likewise.
* lisp/gnus/nndoc.el (nndoc-possibly-change-buffer): Likewise.
* lisp/gnus/nndraft.el (nndraft-request-move-article): Likewise.
(nndraft-auto-save-file-name): Likewise.
* lisp/gnus/nneething.el (nneething-get-head): Likewise.
* lisp/gnus/nnfolder.el (nnfolder-request-move-article): Likewise.
(nnfolder-open-nov): Likewise.
* lisp/gnus/nnheader.el (nnheader-init-server-buffer): Likewise.
(nnheader-set-temp-buffer): Likewise.
* lisp/gnus/nnimap.el (nnimap-log-buffer): Likewise.
* lisp/gnus/nnir.el (nnir-run-swish++): Likewise.
(nnir-run-swish-e): Likewise.
(nnir-run-hyrex): Likewise.
(nnir-run-namazu): Likewise.
(nnir-run-notmuch): Likewise.
(nnir-run-find-grep): Likewise.
* lisp/gnus/nnmail.el (nnmail-split-incoming): Likewise.
(nnmail-cache-open): Likewise.
(nnmail-log-split): Likewise.
* lisp/gnus/nnmaildir.el (nnmaildir--with-work-buffer): Likewise.
(nnmaildir--with-nov-buffer): Likewise.
(nnmaildir--with-move-buffer): Likewise.
* lisp/gnus/nnmairix.el (nnmairix-call-mairix-binary): Likewise.
(nnmairix-call-mairix-binary-raw): Likewise.
(nnmairix-replace-group-and-numbers): Likewise.
* lisp/gnus/nnmbox.el (nnmbox-request-move-article): Likewise.
* lisp/gnus/nnmh.el (nnmh-request-move-article): Likewise.
* lisp/gnus/nnml.el (nnml-request-move-article): Likewise.
(nnml-find-group-number): Likewise.
(nnml-get-nov-buffer): Likewise.
(nnml-generate-nov-file): Likewise.
* lisp/gnus/nnrss.el (nnrss-opml-export): Likewise.
* lisp/gnus/nntp.el (nntp-record-command): Likewise.
* lisp/gnus/nnvirtual.el (nnvirtual-retrieve-headers): Likewise.
* lisp/gnus/smime.el (smime-new-details-buffer): Likewise.
(smime-certificate-info): Likewise.
(smime): Likewise.
* lisp/gnus/spam-stat.el (spam-stat-store-current-buffer): Likewise.

Run "TZ=UTC0 admin/update-copyright $(git ls-files)".

* lisp/gnus/gnus-agent.el (gnus-agent-synchronize-group-flags):
Fix indentation.
* lisp/gnus/gnus-util.el (gnus-buffer-exists-p): Define as obsolete
alias of gnus-buffer-live-p.
(gnus-buffer-live-p): If the given argument is or names a live
buffer, return the corresponding buffer object instead of a boolean.
* lisp/gnus/gnus-win.el (gnus-delete-windows-in-gnusey-frames)
(gnus-remove-some-windows): Simplify.
* lisp/gnus/gnus.el (gnus-prune-buffers): Redefine as alias of
gnus-buffers.
(gnus-kill-buffer, gnus-buffers, gnus-group-find-parameter):
* lisp/gnus/gnus-art.el (gnus-kill-sticky-article-buffers)
(gnus-request-article-this-buffer):
* lisp/gnus/gnus-bcklg.el (gnus-backlog-shutdown):
* lisp/gnus/gnus-cus.el (gnus-group-customize)
(gnus-agent-customize-category):
* lisp/gnus/gnus-draft.el (gnus-draft-edit-message):
* lisp/gnus/gnus-group.el (gnus-group-set-mode-line)
(gnus--abort-on-unsaved-message-buffers, gnus-group-compact-group):
* lisp/gnus/gnus-msg.el (gnus-inews-add-send-actions)
(gnus-summary-supersede-article, gnus-copy-article-buffer):
* lisp/gnus/gnus-score.el (gnus-score-edit-current-scores)
(gnus-score-edit-file):
* lisp/gnus/gnus-spec.el (gnus-update-format-specifications):
* lisp/gnus/gnus-srvr.el (gnus-server-compact-server):
* lisp/gnus/gnus-start.el (gnus-clear-system, gnus-dribble-enter)
(gnus-dribble-save, gnus-dribble-clear, gnus-save-newsrc-file):
* lisp/gnus/gnus-sum.el (gnus-summary-setup-buffer)
(gnus-update-summary-mark-positions, gnus-summary-exit)
(gnus-deaden-summary, gnus-kill-or-deaden-summary)
(gnus-summary-next-group):
* lisp/gnus/gnus-win.el (gnus-configure-frame):
* lisp/gnus/mail-source.el (mail-source-movemail):
* lisp/gnus/message.el (message-with-reply-buffer)
(message-with-reply, message-send-and-exit)
(message-send-mail-with-sendmail, message-pop-to-buffer)
(message-do-send-housekeeping, message-forward-make-body-plain)
(message-forward-make-body-mml):
* lisp/gnus/mm-decode.el (mm-display-external, mm-remove-part):
* lisp/gnus/nnbabyl.el (nnbabyl-server-opened)
(nnbabyl-possibly-change-newsgroup, nnbabyl-read-mbox)
(nnbabyl-check-mbox):
* lisp/gnus/nndiary.el (nndiary-save-nov):
* lisp/gnus/nndoc.el (nndoc-close-group)
(nndoc-possibly-change-buffer):
* lisp/gnus/nnfolder.el (nnfolder-close-group, nnfolder-save-nov):
* lisp/gnus/nnimap.el (nnimap-make-process-buffer, nnimap-keepalive)
(nnimap-find-connection):
* lisp/gnus/nnmail.el (nnmail-cache-open, nnmail-cache-close):
* lisp/gnus/nnmbox.el (nnmbox-close-server, nnmbox-server-opened)
(nnmbox-possibly-change-newsgroup, nnmbox-read-mbox):
* lisp/gnus/nnml.el (nnml-save-incremental-nov, nnml-open-nov)
(nnml-save-nov):
* lisp/gnus/nnoo.el (nnoo-server-opened):
* lisp/gnus/nntp.el (nntp-kill-buffer, nntp-make-process-buffer)
(nntp-open-connection, nntp-async-trigger):
* lisp/net/mairix.el (mairix-gnus-fetch-field): Simplify buffer
liveness checking and killing, replacing buffer-name with
buffer-live-p and gnus-buffer-exists-p with gnus-buffer-live-p or
equivalent where applicable.

This also has the side effect that the accessors are now defined as proper
functions rather than as macros, so they can be passed to `mapcar` etc..

* lisp/gnus/nnheader.el (mail-header-number, mail-header-subject)
(mail-header-from, mail-header-date, mail-header-id)
(mail-header-references, mail-header-chars, mail-header-lines)
(mail-header-xref, mail-header-extra): Define via cl-defstruct.
(mail-header-set-number, mail-header-set-subject)
(mail-header-set-from, mail-header-set-date, mail-header-set-id)
(mail-header-set-message-id, mail-header-set-references)
(mail-header-set-chars, mail-header-set-lines, mail-header-set-xref)
(mail-header-set-extra): Remove, use `setf` instead.  All callers adjusted.

* lisp/gnus/gnus-sum.el (gnus-select-newsgroup)
(gnus-summary-pop-limit, gnus-summary-limit-mark-excluded-as-read)
(gnus-summary-find-matching, gnus-find-matching-articles):
* lisp/gnus/gnus-kill.el (gnus-apply-kill-file-internal, gnus-execute):
* lisp/gnus/gnus-score.el (gnus-score-adaptive):
Eta-reduce, now that mail-header-FIELD are functions.

2fcf2df Fix copyright years by hand
26bed8b Update copyright year to 2019
2814292 Fix value of default frame height.  (Bug#33921)

Run 'TZ=UTC0 admin/update-copyright $(git ls-files)'.

Mostly, this replaces magic-number calls like (nth 4 A) with
more-informative calls like (file-attribute-access-time A).
It also fixes some documentation and minor timestamp coding
issues that I noticed while looking into this.
* doc/lispref/files.texi (File Attributes):
* lisp/files.el (file-attribute-size)
(file-attribute-inode-number, file-attribute-device-number):
* src/dired.c (Fdirectory_files_and_attributes)
(Ffile_attributes):
Mention which attributes must be integers, or nonnegative integers,
as opposed to merely being numbers.  Remove no-longer-correct
talk about representing large integers as conses of integers.
* doc/lispref/files.texi (Magic File Names):
* doc/misc/gnus.texi (Low-level interface to the spam-stat dictionary):
* lisp/autorevert.el (auto-revert-find-file-function)
(auto-revert-tail-mode, auto-revert-handler):
* lisp/auth-source.el (auth-source-netrc-parse):
* lisp/cedet/ede/files.el (ede--inode-for-dir):
* lisp/cedet/semantic/db-file.el (object-write):
* lisp/cedet/semantic/db-mode.el (semanticdb-kill-hook):
* lisp/cedet/semantic/db.el (semanticdb-needs-refresh-p)
(semanticdb-synchronize):
* lisp/cedet/srecode/table.el (srecode-mode-table-new):
* lisp/desktop.el (desktop-save, desktop-read):
* lisp/dired-aux.el (dired-file-set-difference)
(dired-do-chxxx, dired-do-chmod, dired-copy-file-recursive)
(dired-create-files):
* lisp/dired.el (dired-directory-changed-p, dired-readin):
* lisp/dos-w32.el (w32-direct-print-region-helper):
* lisp/emacs-lisp/autoload.el (autoload-generate-file-autoloads)
(autoload-find-destination, update-directory-autoloads):
* lisp/emacs-lisp/shadow.el (load-path-shadows-same-file-or-nonexistent):
* lisp/epg.el (epg--start, epg-wait-for-completion):
* lisp/eshell/em-ls.el (eshell-ls-filetype-p)
(eshell-ls-applicable, eshell-ls-size-string)
(eshell-ls-file, eshell-ls-dir, eshell-ls-files)
(eshell-ls-entries):
* lisp/eshell/em-pred.el (eshell-predicate-alist)
(eshell-pred-file-type, eshell-pred-file-links)
(eshell-pred-file-size):
* lisp/eshell/em-unix.el (eshell-shuffle-files, eshell/cat)
(eshell-du-sum-directory, eshell/du):
* lisp/eshell/esh-util.el (eshell-read-passwd)
(eshell-read-hosts):
* lisp/files.el (remote-file-name-inhibit-cache)
(find-file-noselect, insert-file-1, dir-locals-find-file)
(dir-locals-read-from-dir, backup-buffer)
(file-ownership-preserved-p, copy-directory)
(read-file-modes):
* lisp/find-lisp.el (find-lisp-format):
* lisp/gnus/gnus-agent.el (gnus-agent-unfetch-articles)
(gnus-agent-read-agentview, gnus-agent-expire-group-1)
(gnus-agent-request-article, gnus-agent-regenerate-group)
(gnus-agent-update-files-total-fetched-for)
(gnus-agent-update-view-total-fetched-for):
* lisp/gnus/gnus-cache.el (gnus-cache-read-active)
(gnus-cache-update-file-total-fetched-for)
(gnus-cache-update-overview-total-fetched-for):
* lisp/gnus/gnus-cloud.el (gnus-cloud-file-new-p):
* lisp/gnus/gnus-score.el (gnus-score-score-files):
* lisp/gnus/gnus-start.el (gnus-save-newsrc-file)
(gnus-master-read-slave-newsrc):
* lisp/gnus/gnus-sum.el (gnus-summary-import-article):
* lisp/gnus/gnus-util.el (gnus-file-newer-than)
(gnus-cache-file-contents):
* lisp/gnus/mail-source.el (mail-source-delete-old-incoming)
(mail-source-callback, mail-source-movemail):
* lisp/gnus/nneething.el (nneething-create-mapping)
(nneething-make-head):
* lisp/gnus/nnfolder.el (nnfolder-read-folder):
* lisp/gnus/nnheader.el (nnheader-file-size)
(nnheader-insert-nov-file):
* lisp/gnus/nnmail.el (nnmail-activate):
* lisp/gnus/nnmaildir.el (nnmaildir--group-maxnum)
(nnmaildir--new-number, nnmaildir--update-nov)
(nnmaildir--scan, nnmaildir-request-scan)
(nnmaildir-request-update-info)
(nnmaildir-request-expire-articles):
* lisp/gnus/nnmh.el (nnmh-request-list-1)
(nnmh-request-expire-articles, nnmh-update-gnus-unreads):
* lisp/gnus/nnml.el (nnml-request-expire-articles):
* lisp/gnus/spam-stat.el (spam-stat-save, spam-stat-load)
(spam-stat-process-directory, spam-stat-test-directory):
* lisp/ido.el (ido-directory-too-big-p)
(ido-file-name-all-completions):
* lisp/image-dired.el (image-dired-get-thumbnail-image)
(image-dired-create-thumb-1):
* lisp/info.el (info-insert-file-contents):
* lisp/ls-lisp.el (ls-lisp-insert-directory)
(ls-lisp-handle-switches, ls-lisp-classify-file)
(ls-lisp-format):
* lisp/mail/blessmail.el:
* lisp/mail/feedmail.el (feedmail-default-date-generator)
(feedmail-default-message-id-generator):
* lisp/mail/mailabbrev.el (mail-abbrevs-sync-aliases)
(mail-abbrevs-setup):
* lisp/mail/mspools.el (mspools-size-folder):
* lisp/mail/rmail.el (rmail-insert-inbox-text):
* lisp/mail/sendmail.el (sendmail-sync-aliases):
* lisp/mh-e/mh-alias.el (mh-alias-tstamp):
* lisp/net/ange-ftp.el (ange-ftp-parse-netrc)
(ange-ftp-write-region, ange-ftp-file-newer-than-file-p)
(ange-ftp-cf1):
* lisp/net/eudcb-mab.el (eudc-mab-query-internal):
* lisp/net/eww.el (eww-read-bookmarks):
* lisp/net/netrc.el (netrc-parse):
* lisp/net/newst-backend.el (newsticker--image-get):
* lisp/nxml/rng-loc.el (rng-get-parsed-schema-locating-file):
* lisp/obsolete/fast-lock.el (fast-lock-save-cache):
* lisp/obsolete/vc-arch.el (vc-arch-state)
(vc-arch-diff3-rej-p):
* lisp/org/ob-eval.el (org-babel--shell-command-on-region):
* lisp/org/org-attach.el (org-attach-commit):
* lisp/org/org-macro.el (org-macro-initialize-templates):
* lisp/org/org.el (org-babel-load-file)
(org-file-newer-than-p):
* lisp/org/ox-html.el (org-html-format-spec):
* lisp/org/ox-publish.el (org-publish-find-date)
(org-publish-cache-ctime-of-src):
* lisp/pcmpl-gnu.el (pcomplete/tar):
* lisp/pcmpl-rpm.el (pcmpl-rpm-packages):
* lisp/play/cookie1.el (cookie-snarf):
* lisp/progmodes/cmacexp.el (c-macro-expansion):
* lisp/ps-bdf.el (bdf-file-mod-time):
* lisp/server.el (server-ensure-safe-dir):
* lisp/simple.el (shell-command-on-region):
* lisp/speedbar.el (speedbar-item-info-file-helper)
(speedbar-check-obj-this-line):
* lisp/thumbs.el (thumbs-cleanup-thumbsdir):
* lisp/time.el (display-time-mail-check-directory)
(display-time-file-nonempty-p):
* lisp/url/url-cache.el (url-is-cached):
* lisp/url/url-file.el (url-file-asynch-callback):
* lisp/vc/diff-mode.el (diff-delete-if-empty):
* lisp/vc/pcvs-info.el (cvs-fileinfo-from-entries):
* lisp/vc/vc-bzr.el (vc-bzr-state-heuristic):
* lisp/vc/vc-cvs.el (vc-cvs-checkout-model)
(vc-cvs-state-heuristic, vc-cvs-merge-news)
(vc-cvs-retrieve-tag, vc-cvs-parse-status, vc-cvs-parse-entry):
* lisp/vc/vc-hg.el (vc-hg--slurp-hgignore-1)
(vc-hg--ignore-patterns-valid-p)
(vc-hg--cached-dirstate-search, vc-hg-state-fast):
* lisp/vc/vc-hooks.el (vc-after-save):
* lisp/vc/vc-rcs.el (vc-rcs-workfile-is-newer):
* lisp/vc/vc-svn.el (vc-svn-merge-news, vc-svn-parse-status):
* lisp/vc/vc.el (vc-checkout, vc-checkin, vc-revert-file):
* lisp/xdg.el (xdg-mime-apps):
Prefer (file-attribute-size A) to (nth 7 A), and similarly
for other file attributes accessors.
* doc/lispref/files.texi (File Attributes):
* doc/lispref/intro.texi (Version Info):
* doc/lispref/os.texi (Idle Timers):
* lisp/erc/erc.el (erc-string-to-emacs-time):
* lisp/files.el (file-attribute-access-time)
(file-attribute-modification-time)
(file-attribute-status-change-time):
* lisp/net/tramp-compat.el:
(tramp-compat-file-attribute-modification-time)
(tramp-compat-file-attribute-size):
* src/buffer.c (syms_of_buffer):
* src/editfns.c (Fget_internal_run_time):
* src/fileio.c (Fvisited_file_modtime)
(Fset_visited_file_modtime):
* src/keyboard.c (Fcurrent_idle_time):
* src/process.c (Fprocess_attributes):
Defer implementation details about timestamp format to the
section that talks about timestamp format, to make it easier
to change the documentation later if timestamp formats are
extended.
* lisp/gnus/gnus-util.el (gnus-file-newer-than):
* lisp/speedbar.el (speedbar-check-obj-this-line):
* lisp/vc/vc-rcs.el (vc-rcs-workfile-is-newer):
Prefer time-less-p to doing it by hand.
* lisp/ls-lisp.el (ls-lisp-format): Inode numbers are no longer conses.
* lisp/vc/vc-bzr.el (vc-bzr-state-heuristic):
Use eql, not eq, to compare integers that might be bignums.
* lisp/org/ox-publish.el (org-publish-cache-ctime-of-src):
Prefer float-time to doing time arithmetic by hand.

* lisp/gnus/nnfolder.el (nnfolder-read-folder): Fix previous
checkin that left `active' unbound before using it.