This issue will track Ruby 2.6 support for JRuby. This will be released in JRuby 9.3.0.0

As with previous releases, we will base our checklist on MRI's NEWS file: https://github.com/ruby/ruby/blob/ruby_2_6/NEWS
This bug will track all NEWS items new in Ruby 2.6. This list is based off https://github.com/ruby/ruby/blob/ruby_2_6/NEWS.

Only changes relevant to JRuby are listed here. MRI-specific internal changes and features are not included.

NOTE: Pull requests should be done against the ruby-2.6 branch. That branch will be merged via #6037.

Language changes

• Refinements take place at block passing Feature #14223
• Refinements take place at Kernel#public_send Feature #15326
• Refinements take place at Kernel#respond_to? Feature #15327
• else without rescue causes a syntax error [Experimental] Feature #14606
• Constant names may start with a non-ASCII capital letter Feature #13770
• Endless ranges are introduced. Range that has no end, like (0..) or (0...) Feature #12912
• Non-Symbol keys in a keyword arguments hash cause an exception.
• The “shadowing outer local variable” warning is removed. Feature #12490
• Print cause of the exception if the exception is not caught and printed its backtraces and error message. Feature #8257
• The flip-flop syntax is deprecated. Feature #5400

Core classes updates (outstanding ones only)

Array

• Add Array#union and Array#difference instance methods. Feature #14097
• Array#to_h now accepts a block that maps elements to new key/value pairs. Feature #15143
• Array#filter is a new alias for Array#select. Feature #13784
• Array#filter! is a new alias for Array#select!. Feature #13784

Binding

• Added Binding#source_location. Feature #14230

Dir

• Added Dir#each_child and Dir#children instance methods. Feature #13969

Enumerable

• Enumerable#chain returns an enumerator object that iterates over the elements of the receiver and then those of each argument in sequence. Feature #15144
• Enumerable#to_h now accepts a block that maps elements to new key/value pairs. Feature #15143
• Enumerable#filter is a new alias for Enumerable#select. Feature #13784

Enumerator::ArithmeticSequence

• This is a new class to represent a generator of an arithmetic sequence, that is a number sequence defined by a common difference. It can be used for representing what is similar to Python's slice. You can get an instance of this class from Numeric#step and Range#step.

Enumerator::Chain

• This is a new class to represent a chain of enumerables that works as a single enumerator, generated by such methods as Enumerable#chain and Enumerator#+.

Enumerator::Lazy

• Enumerator::Lazy#filter is a new alias for Enumerator::Lazy#select. Feature #13784

Enumerator

• Enumerator#+ returns an enumerator object that iterates over the elements of the receiver and then those of the other operand. Feature #15144

ENV

• ENV.to_h now accepts a block that maps names and values to new keys and values. Feature #15143

Exception

• Exception#full_message takes :highlight and :order options. Bug #14324

Hash

• Hash#merge, Hash#merge!, and Hash#update now accept multiple arguments. Feature #15111
• Hash#to_h now accepts a block that maps keys and values to new keys and values. Feature #15143
• Hash#filter is a new alias for Hash#select. Feature #13784
• Hash#filter! is a new alias for Hash#select!. Feature #13784

IO

• Added new mode character 'x' to open files for exclusive access. Feature #11258

Kernel

• Kernel#then is a new alias for Kernel#yield_self. Feature #14594
• Kernel#Complex, Kernel#Float, Kernel#Integer, and Kernel#Rational take an :exception option to specify the way of error handling. Feature #12732
• Kernel#system takes an :exception option to raise an exception on failure. Feature #14386
• Kernel#system and Kernel#exec do not close non-standard file descriptors (the default of the :close_others option is changed to false, but we still set the FD_CLOEXEC flag on descriptors we create). Misc #14907

KeyError

• KeyError.new accepts :receiver and :key options to set receiver and key in Ruby code. Feature #14313

Method

• Added Method#<< and Method#>> for Proc composition. Feature #6284

Module

• Module#method_defined?, Module#private_method_defined?, and Module#protected_method_defined? now accept the second parameter as optional. Feature #14944

NameError

• NameError.new accepts a :receiver option to set receiver in Ruby code. Feature #14313

NilClass

• NilClass#=~ is added for compatibility. Feature #15231

NoMethodError

• NoMethodError.new accepts a :receiver option to set receiver in Ruby code. Feature #14313

Numeric

• Numeric#step now returns an instance of the Enumerator::ArithmeticSequence class rather than one of the Enumerator class.

OpenStruct

• OpenStruct#to_h now accepts a block that maps keys and values to new keys and values. Feature #15143

Proc

• Added Proc#<< and Proc#>> for Proc composition. Feature #6284
• Proc#call doesn't change $SAFE any more. Feature #14250

Random

• Added Random.bytes. Feature #4938

Range

• Added Range#% instance method. Feature #14697
• Range#=== now uses the #cover? instead of the #include? method. Feature #14575
• Range#cover? now accepts a Range object. Feature #14473
• Range#step now returns an instance of the Enumerator::ArithmeticSequence class rather than one of the Enumerator class.

Regexp/String

• Update Unicode version from 10.0.0 to 11.0.0. Feature #14802
• Updated to 12.0.0 as of ruby/ruby@cff7eef
• Update Emoji version from 5.0 to 11.0.0 Feature #14802

String

• String#crypt is now deprecated. Feature #14915
• String#split yields each substring to the block if given. Feature #4780

Struct

• Struct#to_h now accepts a block that maps keys and values to new keys and values. Feature #15143
• Struct#filter is a new alias for Struct#select. Feature #13784

Time

• Time.new and Time#getlocal accept a timezone object as well as a UTC offset string. Time#+, Time#-, and Time#succ also preserve the timezone. Feature #14850

TracePoint

• “script_compiled” event is supported. Feature #15287
• TracePoint#parameters Feature #14694
• TracePoint#instruction_sequence Feature #15287
• TracePoint#eval_script Feature #15287
• TracePoint#enable accepts new keywords “target:” and “target_line:”.Feature #15289

Stdlib updates (outstanding ones only)

BigDecimal

• BigDecimal() accepts the new keyword “exception:” similar to Float().

Note for the differences among recent versions

The differences among recent versions of bigdecimal. Please select the suitable version of bigdecimal according to the following information.

• 1.3.5 has BigDecimal.new without “exception:” keyword. You can see the deprecation warning of BigDecimal.new when you specify “-w” option. BigDecimal(), BigDecimal.new, and Object#to_d methods are the same.
• 1.4.0 has BigDecimal.new with “exception:” keyword. You always see the deprecation warning of BigDecimal.new. Object#to_d method is different from BigDecimal() and BigDecimal.new.
• 2.0.0 will be released soon after releasing Ruby 2.6.0. This version will not have the BigDecimal.new method.

Bundler

• Add Bundler to Standard Library. Feature #12733
• Use 1.17.2, the latest stable version.

Coverage

• A oneshot_lines mode is added. Feature #15022
• Add :oneshot_lines keyword argument to Coverage.start.
• Add :stop and :clear keyword arguments to Coverage.result. If clear is true, it clears the counters to zero. If stop is true, it disables coverage measurement.
• Coverage.line_stub, which is a simple helper function that creates the “stub” of line coverage from a given source code.

CSV

• Upgrade to 3.0.2. This includes performance improvements especially for writing. Writing is about 2 times faster. See github.com/ruby/csv/blob/master/NEWS.md.

ERB

• Add :trim_mode and :eoutvar keyword arguments to ERB.new. Now non-keyword arguments other than the first one are softly deprecated and will be removed when Ruby 2.5 becomes EOL. Feature #14256
• erb command's -S option is deprecated, and will be removed in the next version.

FileUtils

• FileUtils#cp_lr. Feature #4189

Matrix

• Matrix#antisymmetric?, Matrix#skew_symmetric?
• Matrix#map!, Matrix#collect! Feature #14151
• Matrix#[]=
• Vector#map!, Vector#collect!
• Vector#[]=

Net

• Add :write_timeout keyword argument to Net::HTTP.new. Feature #13396
• Add Net::HTTP#write_timeout and Net::HTTP#write_timeout=. Feature #13396
• Add Net::HTTPClientException to deprecate Net::HTTPServerException, whose name is misleading. Bug #14688

NKF

• Upgrade to nkf v2.1.5

Psych

• Upgrade to Psych 3.1.0

RDoc

• Become about 2 times faster.
• Use SOURCE_DATE_EPOCH to generate files.
• Fix method line number that slipped off.
• Enable --width, --exclude, and --line-numbers that were ignored.
• Add support for blockquote by “>>>” in default markup notation.
• Add support for “Raises” lines in TomDoc notation.
• Fix syntax error output.
• Fix many parsing bugs.

REXML

• Upgrade to REXML 3.1.9. See (github.com/ruby/rexml/blob/master/NEWS.md).
• concat() function: Stringify all arguments before concatenating.
• string() function: Support context node.
• string() function: Support processing instruction node.
• Support "*:#{ELEMENT_NAME}" syntax in XPath 2.0.
• "//#{ELEMENT_NAME}[#{POSITION}]" case
• string() function: Fix function(document) returns nodes that are out of root elements.
• "/ #{ELEMENT_NAME} " case
• "/ #{ELEMENT_NAME} [ #{PREDICATE} ]" case
• "/ #{AXIS}::#{ELEMENT_NAME}" case
• "#{N}-#{M}" case: One or more white spaces were required before "-"
• "/child::node()" case
• "#{FUNCTION}()/#{PATH}" case
• "@#{ATTRIBUTE}/parent::" case
• "name(#{NODE_SET})" case

CSV

• Upgrade to 3.0.4. See (github.com/ruby/csv/blob/master/NEWS.md).

RSS

• RSS::Parser.parse now accepts options as Hash. :validate , :ignore_unknown_element , :parser_class options are available.

RubyGems

• Upgrade to RubyGems 3.0.1
• (blog.rubygems.org/2018/12/19/3.0.0-released.html)
• (blog.rubygems.org/2018/12/23/3.0.1-released.html)

Set

• Set#filter! is a new alias for Set#select!. Feature #13784

URI

• Add URI::File to handle the file URI scheme. Feature #14035

Compatibility issues (excluding feature bug fixes)

Dir

• Dir.glob with '\0'-separated pattern list will be deprecated, and is now warned. Feature #14643

File

• File.read, File.binread, File.write, File.binwrite, File.foreach, and File.readlines do not invoke external commands even if the path starts with the pipe character '|'. Feature #14245

Object

• Object#=~ is deprecated. Feature #15231

Stdlib compatibility issues (excluding feature bug fixes)

These standard libraries have been promoted to default gems.

• e2mmap
• forwardable
• irb
• logger
• matrix
• mutex_m
• ostruct
• prime
• rexml
• rss
• shell
• sync
• thwait
• tracer

BigDecimal

• The following methods are removed.
  • BigDecimal.allocate
  • BigDecimal.ver

• Every BigDecimal object is frozen. Feature #13984
• BigDecimal() parses the given string similar to Float().
• String#to_d parses the receiver string similar to String#to_f.
• BigDecimal.new will be removed in version 2.0.

Pathname

• Pathname#read, Pathname#binread, Pathname#write, Pathname#binwrite, Pathname#each_line and Pathname#readlines do not invoke external commands even if the path starts with the pipe character '|'. This follows Feature #14245