OTP 27.0-rc1

Erlang/OTP 27.0-rc1 is the first release candidate of three before the OTP 27.0 release.

The intention with this release is to get feedback from our users.
All feedback is welcome, even if it is only to say that it works for you.
We encourage users to try it out and give us feedback either by creating an issue at
https://github.com/erlang/otp/issues or by
posting to Erlang Forums.

All artifacts for the release can be downloaded from the
Erlang/OTP Github release
and you can view the new documentation at
https://erlang.org/documentation/doc-15.0-rc1/doc.
You can also install the latest release using kerl like this:

kerl build 27.0-rc1 27.0-rc1.

Erlang/OTP 27 is a new major release with new features, improvements
as well as a few incompatibilities. Some of the new features are
highlighted below.

Many thanks to all contributors!

Highlights

Documentation

EEP-59 has been
implemented. Documentation attributes in source files can now be used
to document functions, types, callbacks, and modules.

The entire Erlang/OTP documentation is now using the new documentation
system.

New language features

• Triple-Quoted Strings has been implemented as per
  EEP 64 to allow a string
  to encompass a complete paragraph.

• Adjacent string literals without intervening white space is now a syntax
  error, to avoid possible confusion with triple-quoted strings.

• Sigils on string literals (both ordinary and triple-quoted) have
  been implemented as per
  EEP 66. For example,
  ~"Björn" or ~b"Björn" are now equivalent to <<"Björn"/utf8>>.

Compiler and JIT improvements

• The compiler will now merge consecutive updates of the same record.

• Safe destructive update of tuples has been implemented in the compiler
  and runtime system. This allows the VM to update tuples in-place when it
  is safe to do so, thus improving performance by doing less copying but
  also by producing less garbage.

• The maybe expression is now enabled by default, eliminating the need
  for enabling the maybe_expr feature.

• Native coverage support has been implemented in the JIT. It will
  automatically be used by the cover tool to reduce the execution
  overhead when running cover-compiled code. There are also new APIs
  to support native coverage without using the cover tool.

• The compiler will now raise a warning when updating record/map literals
  to catch a common mistake. For example, the compiler will now emit a
  warning for #r{a=1}#r{b=2}.

ERTS

• The erl command now supports the -S flag, which is similar to
  the -run flag, but with some of the rough edges filed off.

• By default, escripts will now be compiled instead of interpreted. That
  means that the compiler application must be installed.

• The default process limit has been raised to 1048576 processes.

• The erlang:system_monitor/2 functionality is now able to monitor long
  message queues in the system.

• The obsolete and undocumented support for opening a port to an external
  resource by passing an atom (or a string) as first argument to
  open_port(), implemented by the vanilla driver,
  has been removed. This feature has been scheduled for removal in OTP 27
  since the release of OTP 26.

• The pid field has been removed from erlang:fun_info/1,2.

• Multiple trace sessions are now supported.

STDLIB

• Several new functions that accept funs have been added to module timer.

• The functions is_equal/2, map/2, and filtermap/2 have been added to
  the modules sets, ordsets, and gb_sets.

• There are new efficient ets traversal functions with guaranteed atomicity.
  For example, ets:next/2 followed by ets:lookup/2 can now be replaced
  with ets:next_lookup/1.

• The new function ets:update_element/4 is similar to ets:update_element/3,
  but takes a default tuple as the fourth argument, which will be inserted
  if no previous record with that key exists.

• binary:replace/3,4 now supports using a fun for supplying the
  replacement binary.

• The new function proc_lib:set_label/1 can be used to add a descriptive
  term to any process that does not have a registered name. The name will
  be shown by tools such as c:i/0 and observer, and it will be included
  in crash reports produced by processes using gen_server, gen_statem,
  gen_event, and gen_fsm.

• Added functions to retrieve the next higher or lower key/element from
  gb_trees and gb_sets, as well as returning iterators that start at
  given keys/elements.

common_test

• Calls to ct:capture_start/0 and ct:capture_stop/0 are now synchronous to
  ensure that all output is captured.

• The default CSS will now include a basic dark mode handling if it is
  preferred by the browser.

crypto

• The functions crypto_dyn_iv_init/3 and crypto_dyn_iv_update/3
  that were marked as deprecated in Erlang/OTP 25 have been removed.

dialyzer

• The --gui option for Dialyzer has been removed.

ssl

• The ssl client can negotiate and handle certificate status request (OCSP
  stapling support on the client side).

tools

• There is a new tool tprof, which combines the functionality of eprof
  and cprof under one interface. It also adds heap profiling.

xmerl

• As an alternative to xmerl_xml, a new export module xmerl_xml_indent
  that provides out-of-the box indented output has been added.

For more details about new features and potential incompatibilities see the README.