Ruby 2.7 backport about IRB (#2990)

* [ruby/reline] Sort completion list

#### Legacy mode:

  ```console
  $ irb --legacy
  irb(main):001:0> l[TAB][TAB]
  lambda           load             local_variables  loop
  ```

#### Before this patch:

  ```console
  $ irb
  irb(main):001:0> l[TAB][TAB]
  local_variables
  loop
  lambda
  load
  ```

#### After this patch:

  ```console
  $ irb
  irb(main):001:0> l[TAB][TAB]
  lambda
  load
  local_variables
  loop
  ```

https://github.com/ruby/reline/commit/6074069c7d

* Drop an invalid char as UTF-8

* Add test_completion_with_indent_and_completer_quote_characters

This is for 8a705245e55575d4d310a2e956b89a36a5931971.

* [ruby/irb] Add tests for RubyLex

The set_auto_indent method calculates the correct number of spaces for
indenting a line. We think there might be a few bugs in this method so
we are testing the current functionality to make sure nothing breaks
when we address those bugs.

Example test failure:

```
  1) Failure:
TestIRB::TestRubyLex#test_auto_indent [/Users/Ben/Projects/irb/test/irb/test_ruby_lex.rb:75]:
Calculated the wrong number of spaces for:
 def each_top_level_statement
  initialize_input
  catch(:TERM_INPUT) do
    loop do
      begin
        prompt
        unless l = lex
          throw :TERM_INPUT if @line == ''
        else
.
<10> expected but was
<12>.
```

https://github.com/ruby/irb/commit/752d5597ab

* [ruby/reline] Degenerate the terminal size to [$LINES, $COLUMNS] if it is unknown

This is a workaround for https://github.com/ruby/irb/issues/50

https://github.com/ruby/reline/commit/5725677d1a

* [ruby/irb] Fix newline depth with multiple braces

This commit fixes the check_newline_depth_difference method to multiple
open braces on one line into account. Before this change we were
subtracting from the depth in check_newline_depth_difference on
every open brace. This is the right thing to do if the opening and
closing brace are on the same line. For example in a method definition we
have an opening and closing parentheses we want to add 1 to our depth,
and then remove it.

```
def foo()
end
```

However this isn't the correct behavior when the brace spans multiple
lines. If a brace spans multiple lines we don't want to subtract from
check_newline_depth_difference and we want to treat the braces the same
way as we do `end` and allow check_corresponding_token_depth to pop the
correct depth.

Example of bad behavior:

```
def foo()
  [
  ]
puts 'bar'
end
```

Example of desired behavior:

```
def foo()
  [
  ]
  puts 'bar'
end
```

https://github.com/ruby/irb/commit/7dc8af01e0

* text/readline/test_readline.rb - fix skip on Reline (#2743)

TestRelineAsReadline#test_input_metachar passes on MinGW

* Add "require 'openstruct'" what is forgotten

* [ruby/irb] Fix lib name of OpenStruct

https://github.com/ruby/irb/commit/1f3a84ab6b

* Add load path and require for ruby/ruby

* Rescue EOFError

If C-d is pressed before IRB is ready, IRB crashes because EOFError occurs.

* Complete indented and quoted string correctly

  def foo
    ''.upca[TAB]

This will be completed to be:

  def foo
  ''.upcase

The indent was gone. This commit fixes the bug.

* [ruby/irb] Fix crashing when multiple open braces per line

https://github.com/ruby/irb/issues/55

If we had put multiple open braces on a line the with no closing brace
spaces_of_nest array keeps getting '0' added to it. This means that when
we pop off of this array we are saying that we should be in position zero
for the next line. This is an issue because we don't always want to be
in position 0 after a closing brace.

Example:
```
[[[
]
]
]
```
In the above example the 'spaces_of_nest' array looks like this after
the first line is entered: [0,0,0]. We really want to be indented 4
spaces for the 1st closing brace 2 for the 2nd and 0 for the 3rd. i.e.
we want it to be: [0,2,4].

We also saw this issue with a heredoc inside of an array.

```
[<<FOO]
hello
FOO
```

https://github.com/ruby/irb/commit/80c69c8272

* Support history-size in .inputrc correctly

* Introduce an abstracted structure about the encoding of Reline

The command prompt on Windows always uses Unicode to take input and print
output but most Reline implementation depends on Encoding.default_external.
This commit introduces an abstracted structure about the encoding of Reline.

* Remove an unused setting variable

* Use Reline.encoding_system_needs if exists

* Add tests for vi_insert and vi_add

* Implement vi_insert_at_bol and vi_add_at_eol

* [ruby/reline] Implement vi_to_next_char

https://github.com/ruby/reline/commit/066ecb0a21

* [ruby/reline] Implement vi_prev_char and vi_to_prev_char

https://github.com/ruby/reline/commit/0ad3ee63fa

* [ruby/readline-ext] Include ruby/assert.h in ruby/ruby.h so that assertions can be there

https://github.com/ruby/readline-ext/commit/4d44c12832

* Stop using minitest dependent methods

* Skip a test that uses assert_ruby_status if it doesn't exist

* Use omit instead of skip

* Check DONT_RUN_RELINE_TEST envvar

* [ruby/irb] Add newline_before_multiline_output

https://github.com/ruby/irb/commit/9eb1801a66

* [ruby/irb] Fix compatibility with rails before 5.2

Rails before 5.2 added Array#append as an alias to Array#<< ,
so that it expects only one argument.
However ruby-2.5 added Array#append as an alias to Array#push
which takes any number of arguments.

If irb completion is used in `rails c` (for example "IO.<tab>")
it fails with:
  irb/completion.rb:206:in `<<': wrong number of arguments (given 3, expected 1) (ArgumentError)

Using Array#push instead of Array#append fixes compatibility.

https://github.com/ruby/irb/commit/5b7bbf9c34

* Reline: Use a more robust detection of MinTTY

The previous detection per get_screen_size fails when stdout is passed
to a pipe. That is the case when running ruby tests in parallel ("-j" switch).
In this case Reline believes that it's running on MinTTY and the tests
are running with ANSI IOGate instead of the Windows adapter on MINGW.
So parallel test results were different to that of a single process.
This commit fixes these differencies.

The code is taken from git sources and translated to ruby.
NtQueryObject() is replaced by GetFileInformationByHandleEx(), because
NtQueryObject() is undocumented and is more difficult to use:
  https://github.com/git-for-windows/git/blob/c5a03b1e29c69f3f06c8fabd92493edb73469176/compat/winansi.c#L558

* Reline: Fix changed test results due to change to UTF-8 on Windows

In commit f8ea2860b0cac1aec79978e6c44168802958e8af the Reline encoding
for native windows console was changed to hardcoded UTF-8.
This caused failures in reline and readline tests, but they were hidden,
because parallel ruby tests incorrectly used Reline::ANSI as IOGate.
Tests failures were raised in single process mode, but not with -j switch.

This patch corrects encodings on native Windows console.

* [ruby/irb] [ruby/irb] Rewrite an expression to detect multiline

https://github.com/ruby/irb/commit/ed5cf375a6

https://github.com/ruby/irb/commit/5b7bbf9c34

* [ruby/reline] Implement vi_change_meta

https://github.com/ruby/reline/commit/8538e0e10f

* Always refer to Reline::IOGate.encoding

* Always use UTF-8 for Reline::GeneralIO on Windows

* Use test_mode on Reline::History::Test for encoding

* [ruby/reline] Support GNOME style Home/End key sequences [Bug #16510]

https://github.com/ruby/reline/commit/788f0df845

* [ruby/irb] Add a new easter egg: dancing ruby

https://github.com/ruby/irb/commit/e37dc7e58e

* [ruby/irb] Exclude useless files from RDoc

https://github.com/ruby/irb/commit/8f1ab2400c

* [ruby/irb] Exclude useless files from RDoc

* Fix inaccuracy in encoding tests

These tests assume
  Encoding.find('locale') == Encoding.find('external')
and fail if they are distinct.

* [ruby/reline] Fix Reline::Windows#scroll_down

I mistook Right and Bottom.

https://github.com/ruby/reline/commit/8be401c5f5

* [ruby/reline] Bypass cursor down when a char is rendered at eol on Windows

A newline is automatically inserted if a character is rendered at eol on
Windows command prompt.

https://github.com/ruby/reline/commit/4bfea07e4a

* [ruby/reline] Organize special keys escape sequences

https://github.com/ruby/reline/commit/41deb1a3d9

* [ruby/readline-ext] Remove unnecessary -I$(top_srcdir) when it's an individual gem

https://github.com/ruby/readline-ext/commit/efaca4a5f4

* [ruby/readline-ext] Check TestRelineAsReadline existance

https://github.com/ruby/readline-ext/commit/c0a6303168

* [ruby/readline-ext] The ruby/assert.h is adopted by Ruby 2.7 or later

https://github.com/ruby/readline-ext/commit/106c31fc1b

* Revert "[ruby/readline-ext] Include ruby/assert.h in ruby/ruby.h so that assertions can be there"

This reverts commit 425b2064d394639101854c83a061a0918b33b857.

This cherry-pick was a mistake.

* [ruby/readline-ext] Use require check instead of DONT_RUN_RELINE_TEST env

https://github.com/ruby/readline-ext/commit/1df99d1481

* [ruby/readline-ext] Add spec.extensions

https://github.com/ruby/readline-ext/commit/8c33abb13c

* [ruby/readline-ext] Use rake/extensiokntask to build

https://github.com/ruby/readline-ext/commit/b0b5f709bd

* Fix readline build dependency

* [ruby/irb] Add test_complete_symbol

https://github.com/ruby/irb/commit/dbbf086c1f

* [ruby/irb] Check doc namespace correctly

IRB::InputCompletor::PerfectMatchedProc crashes when doc not found because a
variable name was incorrect.

https://github.com/ruby/irb/commit/889fd4928f

* [ruby/irb] Fix auto indent with closed brace

A closed brace in auto-indent shouldn't affect the next brace in the same line,
but it behaves like below:

  p() {
    }

It's a bug.

https://github.com/ruby/irb/commit/fbe59e344f

* [ruby/irb] Use 0.step instead of (..0).each for Ruby 2.5

https://github.com/ruby/irb/commit/5d628ca40e

* Revert "[ruby/irb] Add test_complete_symbol"

This reverts commit 3af3431c2c145134996e66f3d8d9ade8ad81bde0.

* [ruby/irb] fix reserved words and completion for them

https://github.com/ruby/irb/commit/6184b227ad

* Add test_complete_symbol

The previous version of the test method used a symbol, ":abcdefg" to complete
but longer symbols that can be completed are defined by other test methods of
other libs.

* test/irb/test_completion.rb: suppress a warning: unused literal ignored

* [ruby/reline] Use IO#write instead of IO#print

IO#print always adds a string of $\ automatically.

https://github.com/ruby/reline/commit/a93119c847

* [ruby/irb] Version 1.2.2

https://github.com/ruby/irb/commit/a71753f15a

* [ruby/reline] Version 0.1.3

https://github.com/ruby/reline/commit/ea2b182466

* [ruby/irb] Include easter-egg.rb in gemspec

`irb` doesn't run because this file isn't included in the gem.
https://github.com/ruby/irb/commit/73cda56d25

* [ruby/irb] Version 1.2.3

https://github.com/ruby/irb/commit/dd56e06df5

* support multi-run test for test_readline.rb

* [ruby/irb] `yield` outside method definition is a syntax error

https://github.com/ruby/irb/commit/dbc7b059c7

* test/readline - allow ENV control of test class creation

In ruby/ruby, the tests run on both readline & reline by creating four test classes:
```
TestReadline
TestReadlineHistory

TestRelineAsReadline
TestRelineAsReadlineHistory
```

Reline inports the test files and uses them in its CI.  Adding the ENV control allows it to only run the `TestRelineAsReadline` classes.

* Omit test_using_quoting_detection_proc_with_multibyte_input temporarily for random order test

* support random order test.

test_readline:
  HISTORY should be empty.

test_using_quoting_detection_proc:
test_using_quoting_detection_proc_with_multibyte_input:
  Readline.completer_quote_characters= and
  Readline.completer_word_break_characters= doesn't accept nil,
  so skip if previous values are nil.

* Set Readline.completion_append_character = nil always

GNU Readline add a white space when Readline.completion_append_character is
not initialized.

* Fix a typo [ci skip]

* skip test if Reline.completion_proc is nil.

Some other tests can set Reline.completion_proc, so if it is nil,
simply skip this test.

* Reset Reline.point

TestRelineAsReadline#test_insert_text expects Readline.point == 0
at the beginning of the test, but a test violate this assumption.

* Convert incompatible encoding symbol names

* Ignore incompatible convert of symbols

* Add workaround for test-bundler failure

https://github.com/ruby/actions/runs/500526558?check_suite_focus=true#step:16:127
```
Failures:

  1) Bundler.setup when Bundler is bundled doesn't blow up
     Failure/Error: expect(err).to be_empty

       expected `"fatal: not a git repository (or any of the parent directories): .git\nfatal: not a git repository (o...the parent directories): .git\nfatal: not a git repository (or any of the parent directories): .git".empty?` to return true, got false

       Commands:
       $ /home/runner/work/actions/actions/snapshot-master/ruby \
         -I/home/runner/work/actions/actions/snapshot-master/lib:/home/runner/work/actions/actions/snapshot-master/spec/bundler \
         -rsupport/hax -rsupport/artifice/fail \
         /home/runner/work/actions/actions/snapshot-master/libexec/bundle install --retry 0
       Resolving dependencies...
       Using bundler 2.1.4
       Bundle complete! 1 Gemfile dependency, 1 gem now installed.
       Use `bundle info [gemname]` to see where a bundled gem is installed.
       fatal: not a git repository (or any of the parent directories): .git
       fatal: not a git repository (or any of the parent directories): .git
       fatal: not a git repository (or any of the parent directories): .git
       # $? => 0

       $ /home/runner/work/actions/actions/snapshot-master/ruby \
         -I/home/runner/work/actions/actions/snapshot-master/lib:/home/runner/work/actions/actions/snapshot-master/spec/bundler \
         -rsupport/hax -rsupport/artifice/fail \
         /home/runner/work/actions/actions/snapshot-master/libexec/bundle exec ruby -e \
         require\ \'bundler\'\;\ Bundler.setup
       fatal: not a git repository (or any of the parent directories): .git
       fatal: not a git repository (or any of the parent directories): .git
       fatal: not a git repository (or any of the parent directories): .git
       # $? => 0
     # ./spec/bundler/runtime/setup_spec.rb:1056:in `block (3 levels) in <top (required)>'
     # ./spec/bundler/spec_helper.rb:111:in `block (3 levels) in <top (required)>'
     # ./spec/bundler/spec_helper.rb:111:in `block (2 levels) in <top (required)>'
     # ./spec/bundler/spec_helper.rb:78:in `block (2 levels) in <top (required)>'
make: *** [yes-test-bundler] Error 1
```

* [ruby/irb] Unnamed groups are not captured when named groups are used

https://github.com/ruby/irb/commit/0a641a69b0

* [ruby/reline] Work with wrong $/ value correctly

https://github.com/ruby/reline/commit/962ebf5a1b

* [ruby/irb] Detect multiple lines output simplify

The old implementation performance test code:

    require 'objspace'
    puts "%.5g MB" % (ObjectSpace.memsize_of_all * 0.001 * 0.001)
    /\A.*\Z/ !~ ('abc' * 20_000_000)
    puts "%.5g MB" % (ObjectSpace.memsize_of_all * 0.001 * 0.001)

and run `time test.rb`:

    2.5868 MB
    62.226 MB

    real    0m1.307s
    user    0m0.452s
    sys     0m0.797s

The new implementation performance test code:

    require 'objspace'
    puts "%.5g MB" % (ObjectSpace.memsize_of_all * 0.001 * 0.001)
    ('abc' * 20_000_000).include?("\n")
    puts "%.5g MB" % (ObjectSpace.memsize_of_all * 0.001 * 0.001)

and run `time test.rb`:

    2.5861 MB
    62.226 MB

    real    0m0.132s
    user    0m0.088s
    sys     0m0.042s

https://github.com/ruby/irb/commit/40d6610baf

* [ruby/reline] Suppress error in case INPUTRC env is empty

https://github.com/ruby/reline/commit/bce7e7562b

* [ruby/reline] Add yamatanooroti rendering test

https://github.com/ruby/reline/commit/f092519525

* [ruby/reline] Rename test suite name of yamatanooroti test

https://github.com/ruby/reline/commit/b0f32f5de4

* [ruby/reline] Add a comment why rescue yamatanooroti loading error on the test

https://github.com/ruby/reline/commit/2a8061daec

* [ruby/irb] Suppress crashing when EncodingError has occurred without lineno

https://github.com/ruby/irb/commit/13572d8cdc

* [ruby/reline] Suppress error when check ambiguous char width in LANG=C

https://github.com/ruby/reline/commit/623dffdd75

* [ruby/io-console] Enable only interrupt bits on `intr: true`

https://github.com/ruby/io-console/commit/baaf929041

* [ruby/io-console] bump up to 0.5.4

* [ruby/io-console] Update the minimum requirement of Ruby version

https://github.com/ruby/io-console/commit/73e7b6318a

* [ruby/io-console] Filter Ruby engine name rather than just /ruby/

This breaks tests using this path on JRuby because the `jruby`
executable turns into `jjruby` after the sub.

https://github.com/ruby/io-console/commit/e5951aa34c

* [ruby/io-console] bump up to 0.5.5

* [ruby/io-console] Prefer keyword arguments

https://github.com/ruby/io-console/commit/5facbfc4c8

* [ruby/io-console] [DOC] Improved about `intr:`

https://github.com/ruby/io-console/commit/82b630cd79

* [ruby/io-console] Just ignore the extension on other than CRuby

https://github.com/ruby/io-console/commit/41b6f09574

* [ruby/io-console] bump up to 0.5.6

Co-authored-by: KOBAYASHI Shuji <shuujii@gmail.com>
Co-authored-by: Ben <kanobt61@gmail.com>
Co-authored-by: Yusuke Endoh <mame@ruby-lang.org>
Co-authored-by: MSP-Greg <MSP-Greg@users.noreply.github.com>
Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>
Co-authored-by: Kenta Murata <mrkn@mrkn.jp>
Co-authored-by: Lars Kanis <lars@greiz-reinsdorf.de>
Co-authored-by: Lars Kanis <kanis@comcard.de>
Co-authored-by: Alan Wu <XrXr@users.noreply.github.com>
Co-authored-by: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Co-authored-by: Nobuhiro IMAI <nov@yo.rim.or.jp>
Co-authored-by: Nick Lewis <nick@puppet.com>
Co-authored-by: S-H-GAMELINKS <gamelinks007@gmail.com>
Co-authored-by: Koichi Sasada <ko1@atdot.net>
Co-authored-by: Kazuhiro NISHIYAMA <zn@mbf.nifty.com>
Co-authored-by: Charles Oliver Nutter <headius@headius.com>

4 files changed, 191 insertions, 1 deletions

diff --git a/test/irb/test_color.rb b/test/irb/test_color.rb
index 3ced640004..cb90d29c9d 100644
--- a/test/irb/test_color.rb
+++ b/test/irb/test_color.rb
@@ -29,7 +29,7 @@ module TestIRB
         "def self.foo; bar; end" => "#{GREEN}def#{CLEAR} #{CYAN}#{BOLD}self#{CLEAR}.#{BLUE}#{BOLD}foo#{CLEAR}; bar; #{GREEN}end#{CLEAR}",
         'erb = ERB.new("a#{nil}b", trim_mode: "-")' => "erb = #{BLUE}#{BOLD}#{UNDERLINE}ERB#{CLEAR}.new(#{RED}#{BOLD}\"#{CLEAR}#{RED}a#{CLEAR}#{RED}\#{#{CLEAR}#{CYAN}#{BOLD}nil#{CLEAR}#{RED}}#{CLEAR}#{RED}b#{CLEAR}#{RED}#{BOLD}\"#{CLEAR}, #{MAGENTA}trim_mode:#{CLEAR} #{RED}#{BOLD}\"#{CLEAR}#{RED}-#{CLEAR}#{RED}#{BOLD}\"#{CLEAR})",
         "# comment" => "#{BLUE}#{BOLD}# comment#{CLEAR}",
-        "yield(hello)" => "#{GREEN}yield#{CLEAR}(hello)",
+        "def f;yield(hello);end" => "#{GREEN}def#{CLEAR} #{BLUE}#{BOLD}f#{CLEAR};#{GREEN}yield#{CLEAR}(hello);#{GREEN}end#{CLEAR}",
         '"##@var]"' => "#{RED}#{BOLD}\"#{CLEAR}#{RED}\##{CLEAR}#{RED}\##{CLEAR}@var#{RED}]#{CLEAR}#{RED}#{BOLD}\"#{CLEAR}",
         '"foo#{a} #{b}"' => "#{RED}#{BOLD}\"#{CLEAR}#{RED}foo#{CLEAR}#{RED}\#{#{CLEAR}a#{RED}}#{CLEAR}#{RED} #{CLEAR}#{RED}\#{#{CLEAR}b#{RED}}#{CLEAR}#{RED}#{BOLD}\"#{CLEAR}",
         '/r#{e}g/' => "#{RED}#{BOLD}/#{CLEAR}#{RED}r#{CLEAR}#{RED}\#{#{CLEAR}e#{RED}}#{CLEAR}#{RED}g#{CLEAR}#{RED}#{BOLD}/#{CLEAR}",
diff --git a/test/irb/test_completion.rb b/test/irb/test_completion.rb
index 52bbc7b2cc..a765bbf3a5 100644
--- a/test/irb/test_completion.rb
+++ b/test/irb/test_completion.rb
@@ -25,5 +25,27 @@ module TestIRB
       assert_include(IRB::InputCompletor.retrieve_completion_data("1r.positi", bind: binding), "1r.positive?")
       assert_empty(IRB::InputCompletor.retrieve_completion_data("1i.positi", bind: binding))
     end
+
+    def test_complete_symbol
+      _ = :aiueo
+      assert_include(IRB::InputCompletor.retrieve_completion_data(":a", bind: binding), ":aiueo")
+      assert_empty(IRB::InputCompletor.retrieve_completion_data(":irb_unknown_symbol_abcdefg", bind: binding))
+    end
+
+    def test_complete_symbol_failure
+      assert_nil(IRB::InputCompletor::PerfectMatchedProc.(":aiueo", bind: binding))
+    end
+
+    def test_complete_reserved_words
+      candidates = IRB::InputCompletor.retrieve_completion_data("de", bind: binding)
+      %w[def defined?].each do |word|
+        assert_include candidates, word
+      end
+
+      candidates = IRB::InputCompletor.retrieve_completion_data("__", bind: binding)
+      %w[__ENCODING__ __LINE__ __FILE__].each do |word|
+        assert_include candidates, word
+      end
+    end
   end
 end
diff --git a/test/irb/test_context.rb b/test/irb/test_context.rb
index 693ebbeaea..d03cc30c78 100644
--- a/test/irb/test_context.rb
+++ b/test/irb/test_context.rb
@@ -63,6 +63,13 @@ module TestIRB
       assert_not_match(/rescue _\.class/, e.message)
     end
 
+    def test_evaluate_with_encoding_error_without_lineno
+      assert_raise_with_message(EncodingError, /invalid symbol/) {
+        @context.evaluate(%q[{"\xAE": 1}], 1)
+        # The backtrace of this invalid encoding hash doesn't contain lineno.
+      }
+    end
+
     def test_evaluate_with_onigmo_warning
       assert_warning("(irb):1: warning: character class has duplicated range: /[aa]/\n") do
         @context.evaluate('/[aa]/', 1)
@@ -216,5 +223,36 @@ module TestIRB
       assert(irb.context.echo?, "echo? should be true by default")
       assert(irb.context.echo_on_assignment?, "echo_on_assignment? should be true when IRB.conf[:ECHO_ON_ASSIGNMENT] is set to true")
     end
+
+    def test_multiline_output_on_default_inspector
+      main = Object.new
+      def main.inspect
+        "abc\ndef"
+      end
+      input = TestInputMethod.new([
+        "self"
+      ])
+      irb = IRB::Irb.new(IRB::WorkSpace.new(main), input)
+      irb.context.return_format = "=> %s\n"
+
+      # The default
+      irb.context.newline_before_multiline_output = true
+      out, err = capture_io do
+        irb.eval_input
+      end
+      assert_empty err
+      assert_equal("=> \nabc\ndef\n",
+                   out)
+
+      # No newline before multiline output
+      input.reset
+      irb.context.newline_before_multiline_output = false
+      out, err = capture_io do
+        irb.eval_input
+      end
+      assert_empty err
+      assert_equal("=> abc\ndef\n",
+                   out)
+    end
   end
 end
diff --git a/test/irb/test_ruby_lex.rb b/test/irb/test_ruby_lex.rb
new file mode 100644
index 0000000000..dd5a1f7ca5
--- /dev/null
+++ b/test/irb/test_ruby_lex.rb
@@ -0,0 +1,130 @@
+$LOAD_PATH.unshift File.expand_path('../../lib', __FILE__)
+require 'irb/ruby-lex'
+require 'test/unit'
+require 'ostruct'
+
+module TestIRB
+  class TestRubyLex < Test::Unit::TestCase
+    Row = Struct.new(:content, :current_line_spaces, :new_line_spaces)
+
+    class MockIO
+      def initialize(params, &assertion)
+        @params = params
+        @assertion = assertion
+      end
+
+      def auto_indent(&block)
+        result = block.call(*@params)
+        @assertion.call(result)
+      end
+    end
+
+    def assert_indenting(lines, correct_space_count, add_new_line)
+      lines = lines + [""] if add_new_line
+      last_line_index = lines.length - 1
+      byte_pointer = lines.last.length
+
+      ruby_lex = RubyLex.new()
+      io = MockIO.new([lines, last_line_index, byte_pointer, add_new_line]) do |auto_indent|
+        error_message = "Calculated the wrong number of spaces for:\n #{lines.join("\n")}"
+        assert_equal(correct_space_count, auto_indent, error_message)
+      end
+      ruby_lex.set_input(io)
+      context = OpenStruct.new(auto_indent_mode: true)
+      ruby_lex.set_auto_indent(context)
+    end
+
+    def test_auto_indent
+      input_with_correct_indents = [
+        Row.new(%q(def each_top_level_statement), nil, 2),
+        Row.new(%q(  initialize_input), nil, 2),
+        Row.new(%q(  catch(:TERM_INPUT) do), nil, 4),
+        Row.new(%q(    loop do), nil, 6),
+        Row.new(%q(      begin), nil, 8),
+        Row.new(%q(        prompt), nil, 8),
+        Row.new(%q(        unless l = lex), nil, 10),
+        Row.new(%q(          throw :TERM_INPUT if @line == ''), nil, 10),
+        Row.new(%q(        else), 8, 10),
+        Row.new(%q(          @line_no += l.count("\n")), nil, 10),
+        Row.new(%q(          next if l == "\n"), nil, 10),
+        Row.new(%q(          @line.concat l), nil, 10),
+        Row.new(%q(          if @code_block_open or @ltype or @continue or @indent > 0), nil, 12),
+        Row.new(%q(            next), nil, 12),
+        Row.new(%q(          end), 10, 10),
+        Row.new(%q(        end), 8, 8),
+        Row.new(%q(        if @line != "\n"), nil, 10),
+        Row.new(%q(          @line.force_encoding(@io.encoding)), nil, 10),
+        Row.new(%q(          yield @line, @exp_line_no), nil, 10),
+        Row.new(%q(        end), 8, 8),
+        Row.new(%q(        break if @io.eof?), nil, 8),
+        Row.new(%q(        @line = ''), nil, 8),
+        Row.new(%q(        @exp_line_no = @line_no), nil, 8),
+        Row.new(%q(        ), nil, 8),
+        Row.new(%q(        @indent = 0), nil, 8),
+        Row.new(%q(      rescue TerminateLineInput), 6, 8),
+        Row.new(%q(        initialize_input), nil, 8),
+        Row.new(%q(        prompt), nil, 8),
+        Row.new(%q(      end), 6, 6),
+        Row.new(%q(    end), 4, 4),
+        Row.new(%q(  end), 2, 2),
+        Row.new(%q(end), 0, 0),
+      ]
+
+      lines = []
+      input_with_correct_indents.each do |row|
+        lines << row.content
+        assert_indenting(lines, row.current_line_spaces, false)
+        assert_indenting(lines, row.new_line_spaces, true)
+      end
+    end
+
+    def test_braces_on_their_own_line
+      input_with_correct_indents = [
+        Row.new(%q(if true), nil, 2),
+        Row.new(%q(  [), nil, 4),
+        Row.new(%q(  ]), 2, 2),
+        Row.new(%q(end), 0, 0),
+      ]
+
+      lines = []
+      input_with_correct_indents.each do |row|
+        lines << row.content
+        assert_indenting(lines, row.current_line_spaces, false)
+        assert_indenting(lines, row.new_line_spaces, true)
+      end
+    end
+
+    def test_multiple_braces_in_a_line
+      input_with_correct_indents = [
+        Row.new(%q([[[), nil, 6),
+        Row.new(%q(    ]), 4, 4),
+        Row.new(%q(  ]), 2, 2),
+        Row.new(%q(]), 0, 0),
+        Row.new(%q([<<FOO]), nil, 0),
+        Row.new(%q(hello), nil, 0),
+        Row.new(%q(FOO), nil, 0),
+      ]
+
+      lines = []
+      input_with_correct_indents.each do |row|
+        lines << row.content
+        assert_indenting(lines, row.current_line_spaces, false)
+        assert_indenting(lines, row.new_line_spaces, true)
+      end
+    end
+
+    def test_a_closed_brace_and_not_closed_brace_in_a_line
+      input_with_correct_indents = [
+        Row.new(%q(p() {), nil, 2),
+        Row.new(%q(}), 0, 0),
+      ]
+
+      lines = []
+      input_with_correct_indents.each do |row|
+        lines << row.content
+        assert_indenting(lines, row.current_line_spaces, false)
+        assert_indenting(lines, row.new_line_spaces, true)
+      end
+    end
+  end
+end