NEWS.md

# NEWS for Ruby 3.0.0

This document is a list of user visible feature changes
since the **2.7.0** release, except for bug fixes.

Note that each entry is kept so brief that no reason behind or reference
information is supplied with.  For a full list of changes with all
sufficient information, see the ChangeLog file or Redmine
(e.g. `https://bugs.ruby-lang.org/issues/$FEATURE_OR_BUG_NUMBER`).

## Language changes

* Keyword arguments are now separated from positional arguments.
  Code that resulted in deprecation warnings in Ruby 2.7 will now
  result in ArgumentError or different behavior. [[Feature #14183]]

* Arguments forwarding (`...`) now supports leading arguments.
  [[Feature #16378]]

    ```ruby
    def method_missing(meth, ...)
      send(:"do_#{meth}", ...)
    end
    ```

* Procs accepting a single rest argument and keywords are no longer
  subject to autosplatting.  This now matches the behavior of Procs
  accepting a single rest argument and no keywords.
  [[Feature #16166]]

    ```ruby
    pr = proc{|*a, **kw| [a, kw]}

    pr.call([1])
    # 2.7 => [[1], {}]
    # 3.0 => [[[1]], {}]

    pr.call([1, {a: 1}])
    # 2.7 => [[1], {:a=>1}] # and deprecation warning
    # 3.0 => [[[1, {:a=>1}]], {}]
    ```

* $SAFE is now a normal global variable with no special behavior.
  C-API methods related to $SAFE have been removed.
  [[Feature #16131]]

* yield in singleton class definitions in methods is now a SyntaxError
  instead of a warning. yield in a class definition outside of a method
  is now a SyntaxError instead of a LocalJumpError.  [[Feature #15575]]

* Find pattern is added. [[Feature #16828]]

    ```ruby
    case ["a", 1, "b", "c", 2, "d", "e", "f", 3]
    in [*pre, String => x, String => y, *post]
      p pre  #=> ["a", 1]
      p x    #=> "b"
      p y    #=> "c"
      p post #=> [2, "d", "e", "f", 3]
    end
    ```

* When a class variable is overtaken by the same definition in an
  ancestor class/module, a RuntimeError is now raised (previously,
  it only issued a warning in verbose mode.  Additionally, accessing a
  class variable from the toplevel scope is now a RuntimeError.
  [[Bug #14541]]

* Rightward assignment statement is added.  [EXPERIMENTAL]
  [[Feature #15921]]

    ```ruby
    fib(10) => x
    ```

* Endless method definition is added.  [EXPERIMENTAL]
  [[Feature #16746]]

    ```ruby
    def square(x) = x * x
    ```

## Command line options

### `--help` option

When the environment variable `RUBY_PAGER` or `PAGER` is present and has
non-empty value, and the standard input and output are tty, `--help`
option shows the help message via the pager designated by the value.
[[Feature #16754]]

## Core classes updates

Outstanding ones only.

* Dir

    * Modified method

        * Dir.glob and Dir.[] now sort the results by default, and
          accept `sort:` keyword option.  [[Feature #8709]]

* ENV

    * New method

        * ENV.except, which returns a hash excluding the given keys
          and their values.  [[Feature #15822]]

* Hash

    * Modified method

        * Hash#transform_keys now accepts a hash that maps keys to new
          keys.  [[Feature #16274]]

    * New method

        * Hash#except, which returns a hash excluding the given keys
          and their values.  [[Feature #15822]]

* Kernel

    * Modified method

        * Kernel#clone when called with `freeze: false` keyword will call
          `#initialize_clone` with the `freeze: false` keyword.
          [[Bug #14266]]

        * Kernel#clone when called with `freeze: true` keyword will call
          `#initialize_clone` with the `freeze: true` keyword, and will
          return a frozen copy even if the receiver is unfrozen.
          [[Feature #16175]]

        * Kernel#eval when called with two arguments will use "(eval)"
          for `__FILE__` and 1 for `__LINE__` in the evaluated code.
          [[Bug #4352]]

        * Kernel#lambda now warns if called without a literal block.
          [[Feature #15973]]

* Module

    * Modified method

        * Module#include and #prepend now affect classes and modules that
          have already included or prepended the receiver, mirroring the
          behavior if the arguments were included in the receiver before
          the other modules and classes included or prepended the receiver.
          [[Feature #9573]]

            ```ruby
            class C; end
            module M1; end
            module M2; end
            C.include M1
            M1.include M2
            p C.ancestors #=> [C, M1, M2, Object, Kernel, BasicObject]
            ```

* Symbol

    * Modified method

        * Symbol#to_proc now returns a lambda Proc.
          [[Feature #16260]]

* Warning

    * Modified method

        * Warning#warn now supports a category kwarg.
        [[Feature #17122]]

## Stdlib updates

Outstanding ones only.

* RubyGems

    * Update to RubyGems 3.2.0.pre1

* Bundler

    * Update to Bundler 2.2.0.dev

* Net::HTTP

    * New method

        * Add Net::HTTP#verify_hostname= and Net::HTTP#verify_hostname
          to skip hostname verification.  [[Feature #16555]]

    * Modified method

        * Net::HTTP.get, Net::HTTP.get_response, and Net::HTTP.get_print can
          take request headers as a Hash in the second argument when the first
          argument is a URI.  [[Feature #16686]]

* Tempfile

    * Modified method

        * `Tempfile.open { ... }` will now unlink the file at the end of the
          block (https://github.com/ruby/tempfile/pull/3), such that once the
          block finishes execution nothing leaks.



## Compatibility issues

Excluding feature bug fixes.

* Regexp literals are frozen [[Feature #8948]] [[Feature #16377]]

    ```ruby
    /foo/.frozen? #=> true
    ```

* EXPERIMENTAL: Hash#each consistently yields a 2-element array [[Bug #12706]]

    * Now `{ a: 1 }.each(&->(k, v) { })` raises an ArgumentError
      due to lambda's arity check.
    * This is experimental; if it brings a big incompatibility issue,
      it may be reverted until 2.8/3.0 release.

* When writing to STDOUT redirected to a closed pipe, no broken pipe
  error message will be shown now.  [[Feature #14413]]

* `TRUE`/`FALSE`/`NIL` constants are no longer defined.

* `Integer#zero?` overrides `Numeric#zero?` for optimization.  [[Misc #16961]]

## Stdlib compatibility issues

* Default gems

    * The following libraries are promoted the default gems from stdlib.

        * English
        * erb
        * find
        * io-nonblock
        * io-wait
        * net-ftp
        * net-http
        * net-imap
        * net-protocol
        * optparse
        * rinda
        * set
        * tempfile
        * tmpdir
        * weakref

* Bundled gems

    * net-telnet and xmlrpc have been removed from the bundled gems.
      If you are interested in maintaining them, please comment on
      your plan to https://github.com/ruby/xmlrpc
      or https://github.com/ruby/net-telnet.

* SDBM have been removed from ruby standard library. [[Bug #8446]]

    * The issues of sdbm will be handled at https://github.com/ruby/sdbm

## C API updates

* C API functions related to $SAFE have been removed.
  [[Feature #16131]]

* C API header file `ruby/ruby.h` was split. [[GH-2991]] Should have no impact
  on extension libraries, but users might experience slow compilations.

## Implementation improvements

* New method cache mechanism for Ractor [[Feature #16614]]

  * TODO: ko1 will write details

* The number of hashes allocated when using a keyword splat in
  a method call has been reduced to a maximum of 1, and passing
  a keyword splat to a method that accepts specific keywords
  does not allocate a hash.

* `super` is optimized when the same type of method is called in the previous call
  if it's not refinements or an attr reader or writer.

### JIT

* Native functions shared by multiple methods are deduplicated on JIT compaction.

* Decrease code size of hot paths by some optimizations and partitioning cold paths.

* Not only pure Ruby methods but also some C methods skip pushing a method frame.

  * `Kernel#class`, `Integer#zero?`

* Always generate appropriate code for `==`, `nil?`, and `!` calls depending on
  a receiver class.

* Optimize instance variable access in some core classes like Hash and their subclasses

* Eliminate VM register access on a method return

* Optimize C method call a little

## Miscellaneous changes

* Methods using `ruby2_keywords` will no longer keep empty keyword
  splats, those are now removed just as they are for methods not
  using `ruby2_keywords`.

* Taint deprecation warnings are now issued in regular mode in
  addition to verbose warning mode.  [[Feature #16131]]

* When an exception is caught in the default handler, the error
  message and backtrace are printed in order from the innermost.
  [[Feature #8661]]


[Bug #4352]:      https://bugs.ruby-lang.org/issues/4352
[Feature #8661]:  https://bugs.ruby-lang.org/issues/8661
[Feature #8709]:  https://bugs.ruby-lang.org/issues/8709
[Feature #8948]:  https://bugs.ruby-lang.org/issues/8948
[Feature #9573]:  https://bugs.ruby-lang.org/issues/9573
[Feature #14183]: https://bugs.ruby-lang.org/issues/14183
[Bug #14266]:     https://bugs.ruby-lang.org/issues/14266
[Feature #14413]: https://bugs.ruby-lang.org/issues/14413
[Feature #15575]: https://bugs.ruby-lang.org/issues/15575
[Feature #16131]: https://bugs.ruby-lang.org/issues/16131
[Feature #16166]: https://bugs.ruby-lang.org/issues/16166
[Feature #16260]: https://bugs.ruby-lang.org/issues/16260
[Feature #16274]: https://bugs.ruby-lang.org/issues/16274
[Feature #16377]: https://bugs.ruby-lang.org/issues/16377
[Bug #12706]:     https://bugs.ruby-lang.org/issues/12706
[Feature #15921]: https://bugs.ruby-lang.org/issues/15921
[Feature #16555]: https://bugs.ruby-lang.org/issues/16555
[Feature #16746]: https://bugs.ruby-lang.org/issues/16746
[Feature #16754]: https://bugs.ruby-lang.org/issues/16754
[GH-2991]:        https://github.com/ruby/ruby/pull/2991
[Feature #15822]: https://bugs.ruby-lang.org/issues/15822
[Feature #16378]: https://bugs.ruby-lang.org/issues/16378
[Feature #16828]: https://bugs.ruby-lang.org/issues/16828
[Bug #14541]:     https://bugs.ruby-lang.org/issues/14541
[Feature #16175]: https://bugs.ruby-lang.org/issues/16175
[Feature #15973]: https://bugs.ruby-lang.org/issues/15973
[Feature #16614]: https://bugs.ruby-lang.org/issues/16614
[Feature #16686]: https://bugs.ruby-lang.org/issues/16686
[Misc #16961]:    https://bugs.ruby-lang.org/issues/16961
[Bug #8446]:      https://bugs.ruby-lang.org/issues/8446
[Feature #17122]: https://bugs.ruby-lang.org/issues/17122