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

Copyright (C) 2017-2018 Free Software Foundation, Inc.
See the end of the file for license conditions.

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This file is about changes in Emacs version 27.

See file HISTORY for a list of GNU Emacs versions and release dates.
See files NEWS.26, NEWS.25, ..., 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,

\f
* Installation Changes in Emacs 27.1

** The new configure option '--with-json' adds support for JSON using
the Jansson library.  It is on by default; use 'configure
--with-json=no' to build without Jansson support.  The new JSON
functions 'json-serialize', 'json-insert', 'json-parse-string', and
'json-parse-buffer' are typically much faster than their Lisp
counterparts from json.el.

** Emacs has been ported to the -fcheck-pointer-bounds option of GCC.
This causes Emacs to check bounds of some arrays addressed by its
internal pointers, which can be helpful when debugging the Emacs
interpreter or modules that it uses.  If your platform supports it you
can enable it when configuring, e.g., './configure CFLAGS="-g3 -O2
-mmpx -fcheck-pointer-bounds"' on Intel MPX platforms.

** Emacs now normally uses a C pointer type instead of a C integer
type to implement Lisp_Object, which is the fundamental machine word
type internal to the Emacs Lisp interpreter.  This change aims to
catch typos and support -fcheck-pointer-bounds.  The 'configure'
option --enable-check-lisp-object-type is therefore no longer as
useful and so is no longer enabled by default in developer builds,
to reduce differences between developer and production builds.

\f
* Startup Changes in Emacs 27.1

\f
* Changes in Emacs 27.1

---
** The new option 'tooltip-resize-echo-area' avoids truncating tooltip text
on GUI frames when tooltips are displayed in the echo area.  Instead,
it resizes the echo area as needed to accommodate the full tool-tip
text.

---
** Show modeline tooltips only if the corresponding action applies.
Customize the option 'mode-line-default-help-echo' to restore the old
behavior where the tooltip text is also shown when the corresponding
action does not apply.

+++
** New function 'logcount' calculates an integer's Hamming weight.

+++
** New function 'libxml-available-p'.
This function returns non-nil if libxml support is both compiled in
and available at run time.  Lisp programs should use this function to
detect built-in libxml support, instead of testing for that
indirectly, e.g., by checking that functions like
'libxml-parse-html-region' return nil.

+++
** New function 'fill-polish-nobreak-p', to be used in 'fill-nobreak-predicate'.
It blocks line breaking after a one-letter word, also in the case when
this word is preceded by a non-space, but non-alphanumeric character.

+++
** The limit on repetitions in regexps has been raised to 2^16-1.
It was previously limited to 2^15-1.  For example, the following
regular expression was previously invalid, but is now accepted:

   x\{32768\}

\f
* Editing Changes in Emacs 27.1

---
** New variable 'x-wait-for-event-timeout'.
This controls how long Emacs will wait for updates to the graphical
state to take effect (making a frame visible, for example).

+++
** New user option 'electric-quote-replace-double'.
This option controls whether '"' is replaced in 'electric-quote-mode',
in addition to other quote characters.  If non-nil, ASCII double-quote
characters that quote text "like this" are replaced by double
typographic quotes, “like this”, in text modes, and in comments in
non-text modes.

\f
* Changes in Specialized Modes and Packages in Emacs 27.1

** Ecomplete
*** The ecomplete sorting has changed to a decay-based algorithm.
This can be controlled by the new `ecomplete-sort-predicate' variable.

*** The 'ecompleterc' file is now placed in ~/.emacs.d/ecompleterc by default
Of course it will still find it if you have it in ~/.ecompleterc

** Smtpmail
Authentication mechanisms can be added via external packages, by
defining new cl-defmethod of smtpmail-try-auth-method.

** Footnote-mode
*** Support Hebrew-style footnotes
*** Footnote text lines are now aligned.
Can be controlled via the new variable 'footnote-align-to-fn-text'.

** CSS mode

---
*** A new command 'css-cycle-color-format' for cycling between color
formats (e.g. "black" => "#000000" => "rgb(0, 0, 0)") has been added,
bound to 'C-c C-f'.

** Dired

+++
*** The new user option 'dired-create-destination-dirs' controls whether
'dired-do-copy' and 'dired-rename-file' should create non-existent
directories in the destination.

** Ibuffer

---
*** New filter ibuffer-filter-by-process; bound to '/E'.

** Edebug

+++
*** The runtime behavior of Edebug's instrumentation can be changed
using the new variables 'edebug-behavior-alist',
'edebug-after-instrumentation-function' and
'edebug-new-definition-function'. Edebug's behavior can be changed
globally or for individual definitions.

** Enhanced xterm support

*** New variable 'xterm-set-window-title' controls whether Emacs sets
the XTerm window title.  This feature is experimental and is disabled
by default.

** Gamegrid

** ERT

+++
*** New variable 'ert-quiet' allows to make ERT output in batch mode
less verbose by removing non-essential information.

---
*** Gamegrid now determines its default glyph size based on display
dimensions, instead of always using 16 pixels. As a result, Tetris,
Snake and Pong are more playable on HiDPI displays.

** Filecache

---
*** Completing filenames in the minibuffer via 'C-TAB' now uses the
styles as configured by the variable 'completion-styles'.

** New macros 'thunk-let' and 'thunk-let*'.
These macros are analogue to 'let' and 'let*', but create bindings that
are evaluated lazily.

** Eshell

---
*** Expansion of history event designators is disabled by default.
To restore the old behavior, use

    (add-hook 'eshell-expand-input-functions
              #'eshell-expand-history-references)

** Tramp

+++
*** New connection method "owncloud", which allows to access OwnCloud
or NextCloud hosted files and directories.

\f
* New Modes and Packages in Emacs 27.1

+++
** Emacs can now visit files in archives as if they were directories.
This feature uses Tramp and works only on systems which support GVFS,
i.e. GNU/Linux, roughly spoken.  See the chapter "(tramp) Archive file
names" in the Tramp manual for full documentation of these facilities.

\f
* Incompatible Lisp Changes in Emacs 27.1

** The FILENAME argument to 'file-name-base' is now mandatory and no
longer defaults to 'buffer-file-name'.

---
** The function 'eldoc-message' now accepts a single argument.
Programs that called it with multiple arguments before should pass
them through 'format' first.  Even that is discouraged: for ElDoc
support, you should set 'eldoc-documentation-function' instead of
calling 'eldoc-message' directly.

** Old-style backquotes now generate an error.  They have been
generating warnings for a decade.  To interpret old-style backquotes
as new-style, bind the new variable 'force-new-style-backquotes' to t.

** Defining a Common Lisp structure using 'cl-defstruct' or
'cl-struct-define' whose name clashes with a builtin type (e.g.,
'integer' or 'hash-table') now signals an error.

\f
* Lisp Changes in Emacs 27.1

+++
** New function assoc-delete-all.

** 'print-quoted' now defaults to t, so if you want to see
(quote x) instead of 'x you will have to bind it to nil where applicable.

** To avoid confusion caused by "smart quotes", the reader signals an
error when reading Lisp symbols which begin with one of the following
quotation characters: ‘’‛“”‟〞＂＇.  A symbol beginning with such a
character can be written by escaping the quotation character with a
backslash.  For example:

    (read "‘smart") => (invalid-read-syntax "strange quote" "‘")
    (read "\\‘smart") == (intern "‘smart")

** Internal parsing commands now use syntax-ppss and disregard
open-paren-in-column-0-is-defun-start.  This affects mostly things like
forward-comment, scan-sexps, and forward-sexp when parsing backward.
The new variable 'comment-use-syntax-ppss' can be set to nil to recover the old
behavior if needed.

** The `server-name' and `server-socket-dir' variables are set when a
socket has been pased to Emacs (Bug#24218).

---
** The 'file-system-info' function is now available on all platforms.
instead of just Microsoft platforms.  This fixes a 'get-free-disk-space'
bug on OS X 10.8 and later (Bug#28639).

---
** The function 'get-free-disk-space' returns now a non-nil value for
remote systems, which support this check.

+++
** The function 'make-string' accepts an additional optional argument.
If the optional third argument is non-nil, 'make-string' will produce
a multibyte string even if its second argument is an ASCII character.

** New JSON parsing and serialization functions 'json-serialize',
'json-insert', 'json-parse-string', and 'json-parse-buffer'.  These
are implemented in C using the Jansson library.

---
** The new function `mailcap-file-name-to-mime-type' has been added.
It's a simple convenience function for looking up MIME types based on
file name extensions.

+++
** The new function 'read-answer' accepts either long or short answers
depending on the new customizable variable 'read-answer-short'.

** The function 'load' now behaves correctly when loading modules.
Specifically, it puts the module name into 'load-history', prints
loading messages if requested, and protects against recursive loads.

** New function 'hash-table-contains-p' to check whether a hash table
contains a certain key.

\f
* Changes in Emacs 27.1 on Non-Free Operating Systems

---
** Battery status is now supported in all Cygwin builds.
Previously it was supported only in the Cygwin-w32 build.

** Emacs now handles key combinations involving the macOS "command"
and "option" modifier keys more correctly.

** The special handling of `frame-title-format' on NS where setting it
to `t' would enable the macOS proxy icon has been replaced with a
separate variable, `ns-use-proxy-icon'. `frame-title-format' will now
work as on other platforms.

\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 <https://www.gnu.org/licenses/>.

\f
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