Implement history command

lib/irb/cmd/history.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+require "stringio"
+require_relative "nop"
+require_relative "../pager"
+
+module IRB
+  # :stopdoc:
+
+  module ExtendCommand
+    class History < Nop
+      category "IRB"
+      description "Show the input history."
+
+      def execute(*)
+        output = StringIO.new
+        irb_context.io.class::HISTORY.each_with_index.reverse_each do |input, index|
+          header = "#{index}: "
+          header_length = header.size
+
+          lines = input.split("\n")
+          first_line = header + lines[0]
+
+          truncated_input = lines[1..1]
+          truncated_input << "..." if lines.size > 2
+
+          truncated_input = truncated_input.map do |line|
+            " " * header_length + line
+          end
+
+          output.puts [first_line, *truncated_input].join("\n")
+        end
+
+        Pager.page_content(output.string)
+      end
+    end
+  end
+
+  # :startdoc:
+end

lib/irb/extend-command.rb

@@ -191,6 +191,12 @@ def irb_context
       [
         :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

@@ -971,4 +971,48 @@ def test_edit_with_editor_env_var
       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
+  end
+
 end