Unfinished Ruby 3.1 features

[headius]

This is based on #7015 and includes only the items that we did not finish in time for 9.4.0.

Language changes

• Multiple assignment evaluation order consistency #7440 Multiple assignment evaluation order has been made consistent with single assignment evaluation order. With single assignment, Ruby uses a left-to-right evaluation order. With this code:

• Non main-Ractors can get instance variables (ivars) of classes/modules
  if ivars refer to shareable objects.
  [Feature #17592]

Core classes updates

• TracePoint

  • TracePoint.allow_reentry is added to allow reenter while TracePoint
    callback.
    [Feature #15912]

• Fiber Scheduler

  • Add support for Addrinfo.getaddrinfo using address_resolve hook.
    [Feature #17370]

  • Introduce non-blocking Timeout.timeout using timeout_after hook.
    [Feature #17470]

  • Introduce new scheduler hooks io_read and io_write along with a
    low level IO::Buffer for zero-copy read/write. [Feature #18020]

  • IO hooks io_wait, io_read, io_write, receive the original IO object
    where possible. [Bug #18003]

  • Make Monitor fiber-safe. [Bug #17827]

  • Replace copy coroutine with pthread implementation. [Feature #18015]

Stdlib updates

• Default gems still not supported in JRuby
  • bigdecimal 3.1.1 (Allow installation on JRuby ruby/bigdecimal#169)
  • date 3.2.2 (JRuby support ruby/date#48)
  • etc 1.3.0 (JRuby support ruby/etc#19)
  • fcntl 1.0.1 (JRuby support ruby/fcntl#9)
  • fiddle 1.1.0 (JRuby support ruby/fiddle#104)
  • nkf 0.1.1 (Partial implementation in JRuby, unsure whether this is important)
  • openssl 3.0.0 (jruby-openssl migration ruby/openssl#20 (comment))
  • pathname 0.2.0 (JRuby support ruby/pathname#17)
  • readline 0.0.3 (JRuby support ruby/readline#5)
  • readline-ext 0.1.4 (will be solved along with readline)
  • resolv 0.2.1 (JRuby support ruby/resolv#19)
  • securerandom 0.1.1 (JRuby support ruby/securerandom#9)
  • set 1.0.2 (JRuby support ruby/set#21)
  • tempfile 0.1.2 (JRuby support ruby/tempfile#7)
  • time 0.2.0 (Depends on date)
  • tmpdir 0.1.2 (JRuby support ruby/tmpdir#13)
  • zlib 2.1.1 (JRuby support ruby/zlib#38)
• The following bundled gems are updated.
  • rbs 2.0.0 (Depends on many internals of CRuby)
  • typeprof 0.21.1 (Depends on many internals of CRuby)
• The following default gems are now bundled gems.
  • debug 1.4.0 (Depends on many internals of CRuby in newer versions)
• The following non-updated gems are not yet installable on JRuby.
  • gdbm 2.1.0
  • io-nonblock (JRuby support ruby/io-nonblock#4)
  • syslog 0.1.0 (JRuby support ruby/syslog#1)
  • win32ole 1.8.8 (JRuby support ruby/win32ole#12)

Stdlib compatibility issues

• lib/debug.rb is replaced with debug.gem

Implementation improvements

These do not apply directly to JRuby, but we should check if we have equivalent optimizations in place.

• Inline cache mechanism is introduced for reading class variables.
  [Feature #17763]

• instance_eval and instance_exec now only allocate a singleton class when
  required, avoiding extra objects and improving performance. [GH-5146]

• The performance of Struct accessors is improved. [GH-5131]

• mandatory_only? builtin special form to improve performance on
  builtin methods. [GH-5112]

• Experimental feature Variable Width Allocation in the garbage collector.
  This feature is turned off by default and can be enabled by compiling Ruby
  with flag USE_RVARGC=1 set. [Feature #18045] [Feature #18239]

Debugger

• A new debugger debug.gem is bundled.
  debug.gem is a fast debugger implementation, and it provides many features
  like remote debugging, colorful REPL, IDE (VSCode) integration, and more.
  It replaces lib/debug.rb standard library.

• rdbg command is also installed into bin/ directory to start and control
  debugging execution.

Miscellaneous changes

• lib/objspace/trace.rb is added, which is a tool for tracing the object
  allocation. Just by requiring this file, tracing is started immediately.
  Just by Kernel#p, you can investigate where an object was created.
  Note that just requiring this file brings a large performance overhead.
  This is only for debugging purposes. Do not use this in production.
  [Feature #17762]

• Now exceptions raised in finalizers will be printed to STDERR, unless
  $VERBOSE is nil. [Feature #17798]

• ruby -run -e httpd displays URLs to access. [Feature #17847]

• Add ruby -run -e colorize to colorize Ruby code using
  IRB::Color.colorize_code.