GNU Emacs NEWS -- history of user-visible changes.

Copyright (C) 2014-2017 Free Software Foundation, Inc.
See the end of the file for license conditions.

Please send Emacs bug reports to bug-gnu-emacs@gnu.org.
If possible, use M-x report-emacs-bug.

This file is about changes in Emacs version 26.

See file HISTORY for a list of GNU Emacs versions and release dates.
See files NEWS.25, NEWS.24, NEWS.23, NEWS.22, NEWS.21, NEWS.20,
NEWS.19, NEWS.18, and NEWS.1-17 for changes in older Emacs versions.

You can narrow news to a specific version by calling 'view-emacs-news'
with a prefix argument or by typing C-u C-h C-n.

Temporary note:
+++ indicates that all necessary documentation updates are complete.
    (This means all relevant manuals in doc/ AND lisp doc-strings.)
--- means no change in the manuals is needed.
When you add a new item, use the appropriate mark if you are sure it applies,

+++
** The version number of CC Mode has been changed from 5.33 to
5.32.99, although the software itself hasn't changed.  This aims to
reduce confusion with the standalone CC Mode 5.33 (available from
http://cc-mode.sourceforge.net), which is a more mature version than
the one in Emacs 25.2.

\f
* Installation Changes in Emacs 26.1

** By default libgnutls is now required when building Emacs.
Use 'configure --with-gnutls=no' to build even when GnuTLS is missing.

** GnuTLS version 2.12.2 or later is now required, instead of merely
version 2.6.6 or later.

** The new option 'configure --enable-gcc-warnings=warn-only' causes
GCC to issue warnings without stopping the build.  This behavior is
now the default in developer builds.  As before, use
'--disable-gcc-warnings' to suppress GCC's warnings, and
'--enable-gcc-warnings' to stop the build if GCC issues warnings.

+++
** The Emacs server now has socket-launching support.  This allows
socket based activation, where an external process like systemd can
invoke the Emacs server process upon a socket connection event and
hand the socket over to Emacs.  Emacs uses this socket to service
emacsclient commands.  This new functionality can be disabled with the
configure option '--disable-libsystemd'.

+++
** A systemd user unit file is provided.  Use it in the standard way:
systemctl --user enable emacs
(If your Emacs is installed in a non-standard location, you may
need to copy the emacs.service file to eg ~/.config/systemd/user/)

** New configure option '--disable-build-details' attempts to build an
Emacs that is more likely to be reproducible; that is, if you build
and install Emacs twice, the second Emacs is a copy of the first.
Deterministic builds omit the build date from the output of the
emacs-version and erc-cmd-SV functions, and the leave the following
variables nil: emacs-build-system, emacs-build-time,
erc-emacs-build-time.

** Emacs no longer works on IRIX.  We expect that Emacs users are not
affected by this, as SGI stopped supporting IRIX in December 2013.

\f
* Startup Changes in Emacs 26.1

** New option '--new-daemon'.  This is the same as '--daemon', except
it runs in the foreground and does not fork.  This is intended for
modern init systems such as systemd, which manage many of the traditional
aspects of daemon behavior themselves.  '--old-daemon' is now an alias
for '--daemon'.

\f
* Changes in Emacs 26.1

+++
** The new function 'mapbacktrace' applies a function to all frames of
the current stack trace.

+++
** Emacs now provides a limited form of concurrency with Lisp threads.
Concurrency in Emacs Lisp is "mostly cooperative", meaning that
Emacs will only switch execution between threads at well-defined
times: when Emacs waits for input, during blocking operations related
to threads (such as mutex locking), or when the current thread
explicitly yields.  Global variables are shared among all threads, but
a 'let' binding is thread-local.  Each thread also has its own current
buffer and its own match data.

See the chapter "Threads" in the ELisp manual for full documentation
of these facilities.

+++
** The new function 'file-name-case-insensitive-p' tests whether a
given file is on a case-insensitive filesystem.

+++
** The new user variable 'electric-quote-chars' provides a list
of curved quotes for 'electric-quote-mode', allowing user to choose
the types of quotes to be used.

+++
** The new user variable 'dired-omit-case-fold' allows the user to
customize the case-sensitivity of dired-omit-mode.  It defaults to
the same sensitivity as that of the filesystem for the corresponding
dired buffer.

+++
** Emacs now uses double buffering to reduce flicker when editing and
resizing graphical Emacs frames on the X Window System.  This support
requires the DOUBLE-BUFFER extension, which major X servers have
supported for many years.  If your system has this extension, but an
Emacs built with double buffering misbehaves on some displays you use,
you can disable the feature by adding

  '(inhibit-double-buffering . t)

to default-frame-parameters.  Or inject this parameter into the
selected frame by evaluating this form:

  (modify-frame-parameters nil '((inhibit-double-buffering . t)))

---
The group 'wp', whose label was "text", is now deprecated.
Use the new group 'text', which inherits from 'wp', instead.

+++
** The new function 'call-shell-region' executes a command in an
inferior shell with the buffer region as input.

+++
** The new user option 'shell-command-dont-erase-buffer' controls
if the output buffer is erased between shell commands; if non-nil,
the output buffer is not erased; this variable also controls where
to set the point in the output buffer: beginning of the output,
end of the buffer or save the point.
When 'shell-command-dont-erase-buffer' is nil, the default value,
the behavior of 'shell-command', 'shell-command-on-region' and
'async-shell-command' is as usual.

+++
** The new user option 'mouse-select-region-move-to-beginning'
controls the position of point when double-clicking mouse-1 on the end
of a parenthetical grouping or string-delimiter: the default value nil
keeps point at the end of the region, setting it to non-nil moves
point to the beginning of the region.

+++
** The new user option 'confirm-kill-processes' allows the user to
skip a confirmation prompt for killing subprocesses when exiting
Emacs.  When set to t (the default), Emacs will prompt for
confirmation before killing subprocesses on exit, which is the same
behavior as before.

---
** 'find-library-name' will now fall back on looking at 'load-history'
to try to locate libraries that have been loaded with an explicit path
outside 'load-path'.

+++
** Faces in 'minibuffer-prompt-properties' no longer overwrite properties
in the text in functions like 'read-from-minibuffer', but instead are
added to the end of the face list.  This allows users to say things
like '(read-from-minibuffer (propertize "Enter something: " 'face 'bold))'.

+++
** The new variable 'extended-command-suggest-shorter' has been added
to control whether to suggest shorter 'M-x' commands or not.

---
** icomplete now respects 'completion-ignored-extensions'.

+++
** Non-breaking hyphens are now displayed with the 'nobreak-hyphen'
face instead of the 'escape-glyph' face.

+++
** Approximations to quotes are now displayed with the new 'homoglyph'
face instead of the 'escape-glyph' face.

---
** 'C-x h' ('mark-whole-buffer') will now avoid marking the prompt
part of minibuffers.

---
** 'find-library' now takes a prefix argument to pop to a different
window.

---
** 'process-attributes' on Darwin systems now returns more information.

+++
** Several accessors for the value returned by 'file-attributes'
have been added.  They are: 'file-attribute-type',
'file-attribute-link-number', 'file-attribute-user-id',
'file-attribute-group-id', 'file-attribute-access-time',
'file-attribute-modification-time',
'file-attribute-status-change-time', 'file-attribute-size',
'file-attribute-modes', 'file-attribute-inode-number',
'file-attribute-device-number' and 'file-attribute-collect'.

+++
** The new function 'buffer-hash' computes a fast, non-consing hash of
a buffer's contents.

---
** 'fill-paragraph' no longer marks the buffer as changed unless it
actually changed something.

---
** The locale language name 'ca' is now mapped to the language
environment 'Catalan', which has been added.

---
** 'align-regexp' has a separate history for its interactive argument.
'align-regexp' no longer shares its history with all other
history-less functions that use 'read-string'.

+++
** The networking code has been reworked so that it's more
asynchronous than it was (when specifying :nowait t in
'make-network-process').  How asynchronous it is varies based on the
capabilities of the system, but on a typical GNU/Linux system the DNS
resolution, the connection, and (for TLS streams) the TLS negotiation
are all done without blocking the main Emacs thread.  To get
asynchronous TLS, the TLS boot parameters have to be passed in (see
the manual for details).

Certain process oriented functions (like 'process-datagram-address')
will block until socket setup has been performed.  The recommended way
to deal with asynchronous sockets is to avoid interacting with them
until they have changed status to "run".  This is most easily done
from a process sentinel.

** 'make-network-process' and 'open-network-stream' sometimes allowed
:service to be an integer string (e.g., :service "993") and sometimes
required an integer (e.g., :service 993).  This difference has been
eliminated, and integer strings work everywhere.

** It is possible to disable attempted recovery on fatal signals.

Two new variables support disabling attempts to recover from stack
overflow and to avoid automatic auto-save when Emacs is delivered a
fatal signal.  'attempt-stack-overflow-recovery', if set to 'nil',
will disable attempts to recover from C stack overflows; Emacs will
then crash as with any other fatal signal.
'attempt-orderly-shutdown-on-fatal-signal', if set to 'nil', will
disable attempts to auto-save the session and shut down in an orderly
fashion when Emacs receives a fatal signal; instead, Emacs will
terminate immediately.  Both variables are non-'nil' by default.
These variables are for users who would like to avoid the small
probability of data corruption due to techniques Emacs uses to recover
in these situations.

+++
** File local and directory local variables are now initialized each
time the major mode is set, not just when the file is first visited.
These local variables will thus not vanish on setting a major mode.

+++
** A second dir-local file (.dir-locals-2.el) is now accepted.
See the variable 'dir-locals-file-2' for more information.

+++
** Connection-local variables can be used to specify local variables
with a value depending on the connected remote server.  For details,
see the node "Connection Local Variables" in the ELisp manual.

---
** International domain names (IDNA) are now encoded via the new
puny.el library, so that one can visit web sites with non-ASCII URLs.

+++
** The new 'timer-list' command lists all active timers in a buffer,
where you can cancel them with the 'c' command.

+++
** The new function 'read-multiple-choice' prompts for multiple-choice
questions, with a handy way to display help texts.

+++
** 'switch-to-buffer-preserve-window-point' now defaults to t.

+++
** The new variable 'debugger-stack-frame-as-list' allows displaying
all call stack frames in a Lisp backtrace buffer as lists.  Both
debug.el and edebug.el have been updated to heed to this variable.

+++
** The new variable 'x-ctrl-keysym' has been added to the existing
roster of X keysyms.  It can be used in combination with another
variable of this kind to swap modifiers in Emacs.

---
** New input methods: 'cyrillic-tuvan', 'polish-prefix'.

+++
** File name quoting by adding the prefix "/:" is now possible for the
local part of a remote file name.  Thus, if you have a directory named
"/~" on the remote host "foo", you can prevent it from being
substituted by a home directory by writing it as "/foo:/:/~/file".

+++
** The new variable 'maximum-scroll-margin' allows having effective
settings of 'scroll-margin' up to half the window size, instead of
always restricting the margin to a quarter of the window.

\f
* Editing Changes in Emacs 26.1

+++
** Two new user options 'list-matching-lines-jump-to-current-line' and
'list-matching-lines-current-line-face' to show highlighted the current
line in *Occur* buffer.

+++
** The 'occur' command can now operate on the region.

+++
** New bindings for 'query-replace-map'.
'undo', undo the last replacement; bound to 'u'.
'undo-all', undo all replacements; bound to 'U'.

** 'delete-trailing-whitespace' deletes whitespace after form feed.
In modes where form feed was treated as a whitespace character,
'delete-trailing-whitespace' would keep lines containing it unchanged.
It now deletes whitespace after the last form feed thus behaving the
same as in modes where the character is not whitespace.

** No more prompt about changed file when the file's content is unchanged.
Instead of only checking the modification time, Emacs now also checks
the file's actual content before prompting the user.

\f
* Changes in Specialized Modes and Packages in Emacs 26.1

** TeX: Add luatex and xetex as alternatives to pdftex

** Electric-Buffer-menu

+++
*** Key 'U' is bound to 'Buffer-menu-unmark-all' and key 'M-DEL' is
bound to 'Buffer-menu-unmark-all-buffers'.

** bs

---
*** Two new commands 'bs-unmark-all', bound to 'U', and
'bs-unmark-previous', bound to <backspace>.

** Buffer-menu

+++
*** Two new commands 'Buffer-menu-unmark-all', bound to 'U' and
'Buffer-menu-unmark-all-buffers', bound to 'M-DEL'.

** Gnus

---
*** The .newsrc file will now only be saved if the native select
method is an NNTP select method.

+++
*** A new command for sorting articles by readedness marks has been
added: `C-c C-s C-m C-m'.

** Ibuffer

---
*** New filter commands `ibuffer-filter-by-basename',
`ibuffer-filter-by-file-extension', `ibuffer-filter-by-directory',
`ibuffer-filter-by-starred-name', `ibuffer-filter-by-modified'
and `ibuffer-filter-by-visiting-file'; bound respectively
to '/b', '/.', '//', '/*', '/i' and '/v'.

---
*** Two new commands 'ibuffer-filter-chosen-by-completion'
and `ibuffer-and-filter', the second bound to '/&'.

---
*** The commands `ibuffer-pop-filter', `ibuffer-pop-filter-group',
`ibuffer-or-filter' and `ibuffer-filter-disable' have the alternative
bindings '/<up>', '/S-<up>', '/|' and '/DEL', respectively.

---
*** The data format specifying filters has been extended to allow
explicit logical 'and', and a more flexible form for logical 'not'.
See 'ibuffer-filtering-qualifiers' doc string for full details.

---
*** A new command 'ibuffer-copy-buffername-as-kill'; bound
to 'B'.

---
*** New command 'ibuffer-change-marks'; bound to '* c'.

---
*** A new command 'ibuffer-mark-by-locked' to mark
all locked buffers;  bound to '% L'.

---
*** A new option 'ibuffer-locked-char' to indicate
locked buffers; Ibuffer shows a new column displaying
'ibuffer-locked-char' for locked buffers.

---
*** A new command 'ibuffer-unmark-all-marks' to unmark
all buffers without asking confirmation;  bound to
'U'; 'ibuffer-do-replace-regexp' bound to 'r'.

---
*** A new command 'ibuffer-mark-by-content-regexp' to mark buffers
whose content matches a regexp; bound to '% g'.

---
*** Two new options 'ibuffer-never-search-content-name' and
'ibuffer-never-search-content-mode' used by
'ibuffer-mark-by-content-regexp'.

** Browse-URL

*** Support for opening links to man pages in Man or WoMan mode.

** Comint

---
*** New user option 'comint-move-point-for-matching-input' to control
where to place point after C-c M-r and C-c M-s.

** Compilation mode

---
*** Messages from CMake are now recognized.

** Dired

+++
*** A new option 'dired-always-read-filesystem' default to nil.
If non-nil, buffers visiting files are reverted before search them;
for instance, in 'dired-mark-files-containing-regexp' a non-nil value
of this option means the file is revisited in a temporary buffer;
this temporary buffer is the actual buffer searched: the original buffer
visiting the file is not modified.

+++
*** In wdired, when editing files to contain slash characters,
the resulting directories are automatically created.  Whether to do
this is controlled by the 'wdired-create-parent-directories' variable.

+++
*** 'W' is now bound to 'browse-url-of-dired-file', and is useful for
viewing HTML files and the like.

** Edebug

*** Edebug can be prevented from pausing 1 second after reaching a
breakpoint (e.g. with "f" and "o") by customizing the new option
'edebug-sit-on-break'.

+++
*** New customizable option 'edebug-max-depth'
This allows to enlarge the maximum recursion depth when instrumenting
code.

** Eshell

*** 'eshell-input-filter's value is now a named function
'eshell-input-filter-default', and has a new custom option
'eshell-input-filter-initial-space' to ignore adding commands prefixed
with blank space to eshell history.

** eww

+++
*** New 'M-RET' command for opening a link at point in a new eww buffer.

+++
*** A new 's' command for switching to another eww buffer via the minibuffer.

---
*** The 'o' command ('shr-save-contents') has moved to 'O' to avoid collision
with the 'o' command from 'image-map'.

+++
*** A new command 'C' ('eww-toggle-colors') can be used to toggle
whether to use the HTML-specified colors or not.  The user can also
customize the 'shr-use-colors' variable.

---
*** Images that are being loaded are now marked with gray
"placeholder" images of the size specified by the HTML.  They are then
replaced by the real images asynchronously, which will also now
respect width/height HTML specs (unless they specify widths/heights
bigger than the current window).

** Images

+++
*** Images are automatically scaled before displaying based on the
'image-scaling-factor' variable (if Emacs supports scaling the images
in question).

+++
*** Images inserted with 'insert-image' and related functions get a
keymap put into the text properties (or overlays) that span the
image.  This keymap binds keystrokes for manipulating size and
rotation, as well as saving the image to a file.  These commands are
also available in 'image-mode'.

+++
*** A new library for creating and manipulating SVG images has been
added.  See the "SVG Images" section in the Lisp reference manual for
details.

+++
*** New setf-able function to access and set image parameters is
provided: 'image-property'.

---
*** New commands 'image-scroll-left' and 'image-scroll-right'
for 'image-mode' that complement 'image-scroll-up' and
'image-scroll-down': they have the same prefix arg behavior and stop
at image boundaries.

** Image-Dired

*** Now provides a minor mode 'image-dired-minor-mode' which replaces
the function 'image-dired-setup-dired-keybindings'.

*** Thumbnail generation is now asynchronous
The number of concurrent processes is limited by the variable
'image-dired-thumb-job-limit'.

*** 'image-dired-thumbnail-storage' has a new option 'standard-large'
for generating 256x256 thumbnails according to the Thumbnail Managing
Standard.

*** Inherits movement keys from 'image-mode' for viewing full images.
This includes the usual char, line, and page movement commands.

*** All the -options types have been changed to argument lists
instead of shell command strings.  This change affects
'image-dired-cmd-create-thumbnail-options',
'image-dired-cmd-create-temp-image-options',
'image-dired-cmd-rotate-thumbnail-options',
'image-dired-cmd-rotate-original-options',
'image-dired-cmd-write-exif-data-options',
'image-dired-cmd-read-exif-data-options', and introduces
'image-dired-cmd-pngnq-options', 'image-dired-cmd-pngcrush-options',
'image-dired-cmd-create-standard-thumbnail-options'

*** Recognizes more tools by default, including pngnq-s9 and OptiPNG

*** 'find-file' and related commands now work on thumbnails and
displayed images, providing a default argument of the original file name
via an addition to 'file-name-at-point-functions'.

---
** The default 'Info-default-directory-list' no longer checks some obsolete
directory suffixes (gnu, gnu/lib, gnu/lib/emacs, emacs, lib, lib/emacs)
when searching for info directories.

+++
** The commands that add ChangeLog entries now prefer a VCS root directory
for the ChangeLog file, if none already exists.  Customize
'change-log-directory-files' to nil for the old behavior.

---
** Support for non-string values of 'time-stamp-format' has been removed.

** Message

---
*** 'message-use-idna' now defaults to t (because Emacs comes with
built-in IDNA support now).

---
*** When sending HTML messages with embedded images, and you have
exiftool installed, and you rotate images with EXIF data (i.e.,
JPEGs), the rotational information will be inserted into the outgoing
image in the message.  (The original image will not have its
orientation affected.)

---
*** The 'message-valid-fqdn-regexp' variable has been removed, since
there are now top-level domains added all the time.  Message will no
longer warn about sending emails to top-level domains it hasn't heard
about.

*** 'message-beginning-of-line' (bound to C-a) understands folded headers.
In 'visual-line-mode' it will look for the true beginning of a header
while in non-'visual-line-mode' it will move the point to the indented
header's value.

** Tramp

+++
*** New connection method "sg", which supports editing files under a
different group ID.

+++
*** New connection method "doas" for OpenBSD hosts.

+++
*** New connection method "gdrive", which allows to access Google
Drive onsite repositories.

+++
*** Gateway methods in Tramp have been removed.  Instead, the Tramp
manual documents how to configure ssh and PuTTY accordingly.

+++
Setting the "ENV" environment variable in 'tramp-remote-process-environment'
enables reading of shell initialization files.

---
** 'auto-revert-use-notify' is set back to t in 'global-auto-revert-mode'.

** CSS mode

---
*** Support for completing attribute values, at-rules, bang-rules,
HTML tags, classes and IDs using the 'completion-at-point' command.
Completion candidates for HTML classes and IDs are retrieved from open
HTML mode buffers.

---
*** CSS mode now binds 'C-h S' to a function that will show
information about a CSS construct (an at-rule, property, pseudo-class,
pseudo-element, with the default being guessed from context).  By
default the information is looked up on the Mozilla Developer Network,
but this can be customized using 'css-lookup-url-format'.

+++
** Emacs now supports character name escape sequences in character and
string literals.  The syntax variants \N{character name} and
\N{U+code} are supported.

+++
** Prog mode has some support for multi-mode indentation.
This allows better indentation support in modes that support multiple
programming languages in the same buffer, like literate programming
environments or ANTLR programs with embedded Python code.

A major mode can provide indentation context for a sub-mode through
the 'prog-indentation-context' variable.  To support this, modes that
provide indentation should use 'prog-widen' instead of 'widen' and
'prog-first-column' instead of a literal zero.  See the node
"Mode-Specific Indent" in the ELisp manual for more details.

** ERC

*** New variable 'erc-default-port-tls' used to connect to TLS IRC
servers.

** URL

+++
*** The new function 'url-cookie-delete-cookie' can be used to
programmatically delete all cookies, or cookies from a specific
domain.

+++
*** 'url-retrieve-synchronously' now takes an optional timeout parameter.

---
*** The URL package now support HTTPS over proxies supporting CONNECT.

+++
*** 'url-user-agent' now defaults to 'default', and the User-Agent
string is computed dynamically based on 'url-privacy-level'.

** VC and related modes

---
*** The VC state indicator in the mode line now defaults to more
colorful faces to make it more obvious to the user what the state is.
See the 'vc-faces' customization group.

** CC mode

*** Opening a .h file will turn C or C++ mode depending on language used.
This is done with the help of 'c-or-c++-mode' function which analyses
contents of the buffer to determine whether it's a C or C++ source
file.

** Flymake

+++
*** Emacs does no longer prompt the user before killing Flymake
processes on exit.

\f
* New Modes and Packages in Emacs 26.1

** New Elisp data-structure library 'radix-tree'.

\f
* Incompatible Lisp Changes in Emacs 26.1

+++
** Resizing a frame no longer runs 'window-configuration-change-hook'.
Put your function on 'window-size-change-functions' instead.

** 'C-up', 'C-down', 'C-left' and 'C-right' are now defined in term
mode to send the same escape sequences that xterm does.  This makes
things like forward-word in readline work.

---
** hideshow mode got four key bindings that are analogous to outline
mode bindings: 'C-c @ C-a', 'C-c @ C-t', 'C-c @ C-d', and 'C-c @ C-e.'

** The grep/rgrep/lgrep functions will now ask about saving files
before running.  This is controlled by the 'grep-save-buffers'
variable.

** Some obsolete functions, variables, and faces have been removed:
*** make-variable-frame-local.  Variables cannot be frame-local any more.
*** From subr.el: window-dot, set-window-dot, read-input, show-buffer,
eval-current-buffer, string-to-int
*** All the default-FOO variables that hold the default value of the
FOO variable.  Use 'default-value' and 'setq-default' to access and
change FOO, respectively.  The exhaustive list of removed variables is:
'default-mode-line-format', 'default-header-line-format',
'default-line-spacing', 'default-abbrev-mode', 'default-ctl-arrow',
'default-truncate-lines', 'default-left-margin', 'default-tab-width',
'default-case-fold-search', 'default-left-margin-width',
'default-right-margin-width', 'default-left-fringe-width',
'default-right-fringe-width', 'default-fringes-outside-margins',
'default-scroll-bar-width', 'default-vertical-scroll-bar',
'default-indicate-empty-lines', 'default-indicate-buffer-boundaries',
'default-fringe-indicator-alist', 'default-fringe-cursor-alist',
'default-scroll-up-aggressively', 'default-scroll-down-aggressively',
'default-fill-column', 'default-cursor-type',
'default-cursor-in-non-selected-windows',
'default-buffer-file-coding-system', 'default-major-mode', and
'default-enable-multibyte-characters'.
*** Many variables obsoleted in 22.1 referring to face symbols

+++
** The variable 'text-quoting-style' no longer affects the treatment
of curved quotes in format arguments to functions like 'message' and
'format-message'.  In particular, when this variable's value is
'grave', all quotes in formats are output as-is.

** Functions like 'check-declare-file' and 'check-declare-directory'
now generate less chatter and more-compact diagnostics.  The auxiliary
function 'check-declare-errmsg' has been removed.

+++
** The regular expression character class [:blank:] now matches
Unicode horizontal whitespace as defined in the Unicode Technical
Standard #18.  If you only want to match space and tab, use [ \t]
instead.

\f
* Lisp Changes in Emacs 26.1

+++
** 'save-some-buffers' now uses 'save-some-buffers-default-predicate'
to decide which buffers to ask about, if the PRED argument is nil.
The default value of 'save-some-buffers-default-predicate' is nil,
which means ask about all file-visiting buffers.

** string-(to|as|make)-(uni|multi)byte are now declared obsolete.
** New variable 'while-no-input-ignore-events' which allow
setting which special events 'while-no-input' should ignore.
It is a list of symbols.

** New function 'undo-amalgamate-change-group' to get rid of
undo-boundaries between two states.

** New var 'definition-prefixes' is a hash table mapping prefixes to
the files where corresponding definitions can be found.  This can be
used to fetch definitions that are not yet loaded, for example for
'C-h f'.

** New var 'syntax-ppss-table' to control the syntax-table used in
'syntax-ppss'.

+++
** 'define-derived-mode' can now specify an :after-hook form, which
gets evaluated after the new mode's hook has run.  This can be used to
incorporate configuration changes made in the mode hook into the
mode's setup.

** Autoload files can be generated without timestamps,
by setting 'autoload-timestamps' to nil.
FIXME As an experiment, nil is the current default.
If no insurmountable problems before next release, it can stay that way.

---
** 'gnutls-boot' now takes a parameter ':complete-negotiation' that
says that negotiation should complete even on non-blocking sockets.

+++
** New functions 'window-pixel-width-before-size-change' and
'window-pixel-height-before-size-change' support detecting which
window changed size when 'window-size-change-functions' are run.

+++
** New function 'display-buffer-reuse-mode-window' is an action function
suitable for use in 'display-buffer-alist'. For example, to avoid creating
a new window when opening man pages when there's already one, use
(add-to-list 'display-buffer-alist
     '("\\`\\*Man .*\\*\\'" .
       (display-buffer-reuse-mode-window
        (inhibit-same-window . nil)
        (mode . Man-mode))))

---
** There is now a new variable 'flyspell-sort-corrections-function'
that allows changing the way corrections are sorted.

---
** The new command 'fortune-message' has been added, which displays
fortunes in the echo area.

+++
** New function 'func-arity' returns information about the argument list
of an arbitrary function.  This generalizes 'subr-arity' for functions
that are not built-in primitives.  We recommend using this new
function instead of 'subr-arity'.

** New function 'region-bounds' can be used in the interactive spec
to provide region boundaries (for rectangular regions more than one)
to an interactively callable function as a single argument instead of
two separate arguments region-beginning and region-end.

+++
** 'parse-partial-sexp' state has a new element.  Element 10 is
non-nil when the last character scanned might be the first character
of a two character construct, i.e., a comment delimiter or escaped
character.  Its value is the syntax of that last character.

+++
** 'parse-partial-sexp's state, element 9, has now been confirmed as
permanent and documented, and may be used by Lisp programs.  Its value
is a list of currently open parenthesis positions, starting with the
outermost parenthesis.

---
** 'read-color' will now display the color names using the color itself
as the background color.

** The function 'redirect-debugging-output' now works on platforms
other than GNU/Linux.

+++
** The new function 'string-version-lessp' compares strings by
interpreting consecutive runs of numerical characters as numbers, and
compares their numerical values.  According to this predicate,
"foo2.png" is smaller than "foo12.png".

+++
** The new function 'char-from-name' converts a Unicode name string
to the corresponding character code.

+++
** New functions 'sxhash-eq' and 'sxhash-eql' return hash codes of a
Lisp object suitable for use with 'eq' and 'eql' correspondingly.  If
two objects are 'eq' ('eql'), then the result of 'sxhash-eq'
('sxhash-eql') on them will be the same.

+++
** Function 'sxhash' has been renamed to 'sxhash-equal' for
consistency with the new functions.  For compatibility, 'sxhash'
remains as an alias to 'sxhash-equal'.

+++
** New function `add-variable-watcher' can be used to call a function
when a symbol's value is changed.  This is used to implement the new
debugger command `debug-on-variable-change'.

+++
** Time conversion functions that accept a time zone rule argument now
allow it to be OFFSET or a list (OFFSET ABBR), where the integer
OFFSET is a count of seconds east of Universal Time, and the string
ABBR is a time zone abbreviation.  The affected functions are
'current-time-string', 'current-time-zone', 'decode-time',
'format-time-string', and 'set-time-zone-rule'.

+++
** 'format-time-string' now formats "%q" to the calendar quarter.

** New built-in function 'mapcan' which avoids unnecessary consing (and garbage
collection).

+++
** 'car' and 'cdr' compositions 'cXXXr' and 'cXXXXr' are now part of Elisp.

---
** 'if-let*', 'when-let*', and 'and-let*' are new in subr-x.el.
The incumbent 'if-let' and 'when-let' are now aliases.

** Low-level list functions like 'length' and 'member' now do a better
job of signaling list cycles instead of looping indefinitely.

+++
** The new functions 'make-nearby-temp-file' and 'temporary-file-directory'
can be used for creation of temporary files of remote or mounted directories.

+++
** The new function 'file-local-name' can be used to specify arguments
of remote processes.

+++
** The new functions 'file-name-quote', 'file-name-unquote' and
'file-name-quoted-p' can be used to quote / unquote file names with
the prefix "/:".

+++
** The new error 'file-missing', a subcategory of 'file-error', is now
signaled instead of 'file-error' if a file operation acts on a file
that does not exist.

+++
** The function 'delete-directory' no longer signals an error when
operating recursively and when some other process deletes the directory
or its files before 'delete-directory' gets to them.

** Changes in Frame- and Window- Handling

+++
*** Support for side windows is now official.  The display action
function 'display-buffer-in-side-window' will display its buffer in a
side window.  Functions for toggling all side windows on a frame,
changing and reversing the layout of side windows and returning the main
(major non-side) window of a frame are provided.  For details consult
the section "Side Windows" in the Elisp manual.

+++
*** Support for atomic windows - rectangular compositions of windows
treated by 'split-window', 'delete-window' and 'delete-other-windows'
like a single live window - is now official.  For details consult the
section "Atomic Windows" in the Elisp manual.

+++
*** New 'display-buffer' alist entry 'window-parameters' allows to
assign window parameters to the window used for displaying the buffer.

+++
*** New window parameter 'no-delete-other-window' prevents that
its window gets deleted by 'delete-other-windows'.

+++
*** New command 'window-swap-states' swaps the states of two live
windows.

\f
* Changes in Emacs 26.1 on Non-Free Operating Systems

** Intercepting hotkeys on Windows 7 and later now works better.
The new keyboard hooking code properly grabs system hotkeys such as
Win-* and Alt-TAB, in a way that Emacs can get at them before the
system.  This makes the 'w32-register-hot-key' functionality work
again on all versions of MS-Windows starting with Windows 7.  On
Windows NT and later you can now register any hotkey combination.  (On
Windows 9X, the previous limitations, spelled out in the Emacs manual,
still apply.)

** 'convert-standard-filename' no longer mirrors slashes on MS-Windows.
Previously, on MS-Windows this function converted slash characters in
file names into backslashes.  It no longer does that.  If your Lisp
program used 'convert-standard-filename' to prepare file names to be
passed to subprocesses (which is not the recommended usage of that
function), you will now have to mirror slashes in your application
code.  One possible way is this:

         (let ((start 0))
           (while (string-match "/" file-name start)
             (aset file-name (match-beginning 0) ?\\)
             (setq start (match-end 0))))

** GUI sessions now treat SIGINT like Posix platforms do.
The effect of delivering a Ctrl-C (SIGINT) signal to a GUI Emacs on
MS-Windows is now the same as on Posix platforms -- Emacs saves the
session and exits.  In particular, this will happen if you start
emacs.exe from the Windows shell, then type Ctrl-C into that shell's
window.

---
** 'signal-process' supports SIGTRAP on Windows XP and later.
The 'kill' emulation on Windows now maps SIGTRAP to a call to the
'DebugBreakProcess' API.  This causes the receiving process to break
execution and return control to the debugger.  If no debugger is
attached to the receiving process, the call is typically ignored.
This is in contrast to the default action on POSIX Systems, where it
causes the receiving process to terminate with a core dump if no
debugger has been attached to it.

\f
----------------------------------------------------------------------
This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

\f
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coding: us-ascii
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