[ruby/irb] Implement `history` command

(https://github.com/ruby/irb/pull/761)

* Implement `history` command

Lists IRB input history with indices. Also aliased as `hist`.

* Add tests for `history` command

* Address feedback: `puts` with multiple arguments instead of `join`ing

* Address feedback: Handle nil from splitting an empty input string

* Refactor line truncation

* Add `-g` grep option to `history` command

* Add `history` command to README

* Remove unused `*args` parameter

* Allow spaces to be included in grep

* Allow `/` to be included in grep regex

* Handle `input` being an empty string

* Exclude "#{index}: " from matching the grep regex

* Add new line after joining

https://github.com/ruby/irb/commit/3f9eacbfa9

2 files changed, 53 insertions, 0 deletions

diff --git a/lib/irb/cmd/history.rb b/lib/irb/cmd/history.rb
new file mode 100644
index 0000000000..5b712fa44d
--- /dev/null
+++ b/lib/irb/cmd/history.rb
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require "stringio"
+require_relative "nop"
+require_relative "../pager"
+
+module IRB
+  # :stopdoc:
+
+  module ExtendCommand
+    class History < Nop
+      category "IRB"
+      description "Shows the input history. `-g [query]` or `-G [query]` allows you to filter the output."
+
+      def self.transform_args(args)
+        match = args&.match(/(-g|-G)\s+(?<grep>.+)\s*\n\z/)
+        return unless match
+
+        "grep: #{Regexp.new(match[:grep]).inspect}"
+      end
+
+      def execute(grep: nil)
+        formatted_inputs = irb_context.io.class::HISTORY.each_with_index.reverse_each.filter_map do |input, index|
+          next if grep && !input.match?(grep)
+
+          header = "#{index}: "
+
+          first_line, *other_lines = input.split("\n")
+          first_line = "#{header}#{first_line}"
+
+          truncated_lines = other_lines.slice!(1..) # Show 1 additional line (2 total)
+          other_lines << "..." if truncated_lines&.any?
+
+          other_lines.map! do |line|
+            " " * header.length + line
+          end
+
+          [first_line, *other_lines].join("\n") + "\n"
+        end
+
+        Pager.page_content(formatted_inputs.join)
+      end
+    end
+  end
+
+  # :startdoc:
+end
diff --git a/lib/irb/extend-command.rb b/lib/irb/extend-command.rb
index 514293a438..072069d4c4 100644
--- a/lib/irb/extend-command.rb
+++ b/lib/irb/extend-command.rb
@@ -191,6 +191,12 @@ module IRB # :nodoc:
       [
         :irb_show_cmds, :ShowCmds, "cmd/show_cmds",
         [:show_cmds, NO_OVERRIDE],
+      ],
+
+      [
+        :irb_history, :History, "cmd/history",
+        [:history, NO_OVERRIDE],
+        [:hist, NO_OVERRIDE],
       ]
     ]