Display show_cmds's output in a pager when in TTY environment

This can:

- Make it easier to scroll up and down the commands list
- Avoid pushing up users' previous output
- Allow users to do basic search with `/<word>`

lib/irb/cmd/show_cmds.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "stringio"
+require "rdoc/ri/driver"
 require_relative "nop"
 
 module IRB
@@ -28,9 +29,30 @@ def execute(*args)
           output.puts
         end
 
-        puts output.string
+        display_content(output.string)
+      end
 
-        nil
+      private
+
+      def display_content(content)
+        if STDIN.tty?
+          begin
+            pid = nil
+            RDoc::RI::Driver.new.page do |io|
+              pid = io.pid
+              io.puts content
+            end
+          # When user presses Ctrl-C, IRB would raise `IRB::Abort`
+          # But because RDoc's pager is implemented by running `pager` or `less` in another process with `IO.popen`,
+          # the `IRB::Abort` exception only interrupts IRB's execution but doesn't affect the pager
+          # So to properly terminate the pager with Ctrl-C, we need to catch `IRB::Abort` and kill the pager process
+          rescue IRB::Abort
+            Process.kill("TERM", pid) if pid
+            nil
+          end
+        else
+          puts content
+        end
       end
     end
   end

test/irb/yamatanooroti/test_rendering.rb

@@ -252,6 +252,24 @@ def test_assignment_expression_truncate
     EOC
   end
 
+  def test_show_cmds_with_pager_can_quit_with_ctrl_c
+    write_irbrc <<~'LINES'
+      puts 'start IRB'
+    LINES
+    start_terminal(40, 80, %W{ruby -I#{@pwd}/lib #{@pwd}/exe/irb}, startup_message: 'start IRB')
+    write("show_cmds\n")
+    write("G") # move to the end of the screen
+    write("\C-c") # quit pager
+    write("'foo' + 'bar'\n") # eval something to make sure IRB resumes
+    close
+
+    screen = result.join("\n").sub(/\n*\z/, "\n")
+    # IRB::Abort should be rescued
+    assert_not_match(/IRB::Abort/, screen)
+    # IRB should resume
+    assert_match(/foobar/, screen)
+  end
+
   private
 
   def write_irbrc(content)