[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

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

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],
       ]
     ]
 

test/irb/test_cmd.rb

@@ -888,4 +888,68 @@ module TestIRB
       assert_match("command: ': code2'", out)
     end
   end
+
+  class HistoryCmdTest < CommandTestCase
+    def teardown
+      TestInputMethod.send(:remove_const, "HISTORY") if defined?(TestInputMethod::HISTORY)
+      super
+    end
+
+    def test_history
+      TestInputMethod.const_set("HISTORY", %w[foo bar baz])
+
+      out, err = without_rdoc do
+        execute_lines("history")
+      end
+
+      assert_include(out, <<~EOF)
+        2: baz
+        1: bar
+        0: foo
+      EOF
+      assert_empty err
+    end
+
+    def test_multiline_history_with_truncation
+      TestInputMethod.const_set("HISTORY", ["foo", "bar", <<~INPUT])
+        [].each do |x|
+          puts x
+        end
+      INPUT
+
+      out, err = without_rdoc do
+        execute_lines("hist")
+      end
+
+      assert_include(out, <<~EOF)
+        2: [].each do |x|
+             puts x
+           ...
+        1: bar
+        0: foo
+      EOF
+      assert_empty err
+    end
+
+    def test_history_grep
+      TestInputMethod.const_set("HISTORY", ["foo", "bar", <<~INPUT])
+        [].each do |x|
+          puts x
+        end
+      INPUT
+
+      out, err = without_rdoc do
+        execute_lines("hist -g each\n")
+      end
+
+      assert_include(out, <<~EOF)
+        2: [].each do |x|
+             puts x
+           ...
+      EOF
+      assert_empty err
+    end
+
+  end
+
 end