Page evaluation result's output (#784)

* Page evaluation result's output

This will make it easier to work with long output that exceeds the terminal's height.

* Use consistent TERM in rendering tests

This makes sure we get consistent result on all platforms.

lib/irb.rb

@@ -20,6 +20,7 @@
 require_relative "irb/version"
 require_relative "irb/easter-egg"
 require_relative "irb/debug"
+require_relative "irb/pager"
 
 # IRB stands for "interactive Ruby" and is a tool to interactively execute Ruby
 # expressions read from the standard input.
@@ -859,11 +860,12 @@ def output_value(omit = false) # :nodoc:
           end
         end
       end
+
       if multiline_p && @context.newline_before_multiline_output?
-        printf @context.return_format, "\n#{str}"
-      else
-        printf @context.return_format, str
+        str = "\n" + str
       end
+
+      Pager.page_content(format(@context.return_format, str), retain_content: true)
     end
 
     # Outputs the local variables to this current session, including

lib/irb/pager.rb

@@ -7,18 +7,18 @@ class Pager
     PAGE_COMMANDS = [ENV['RI_PAGER'], ENV['PAGER'], 'less', 'more'].compact.uniq
 
     class << self
-      def page_content(content)
+      def page_content(content, **options)
         if content_exceeds_screen_height?(content)
-          page do |io|
+          page(**options) do |io|
             io.puts content
           end
         else
           $stdout.puts content
         end
       end
 
-      def page
-        if IRB.conf[:USE_PAGER] && STDIN.tty? && pager = setup_pager
+      def page(retain_content: false)
+        if IRB.conf[:USE_PAGER] && STDIN.tty? && pager = setup_pager(retain_content: retain_content)
           begin
             pid = pager.pid
             yield pager
@@ -55,19 +55,20 @@ def content_exceeds_screen_height?(content)
           pageable_height * screen_width < Reline::Unicode.calculate_width(content, true)
       end
 
-      def setup_pager
+      def setup_pager(retain_content:)
         require 'shellwords'
 
-        PAGE_COMMANDS.each do |pager|
-          pager = Shellwords.split(pager)
-          next if pager.empty?
+        PAGE_COMMANDS.each do |pager_cmd|
+          cmd = Shellwords.split(pager_cmd)
+          next if cmd.empty?
 
-          if pager.first == 'less'
-            pager << '-R' unless pager.include?('-R')
+          if cmd.first == 'less'
+            cmd << '-R' unless cmd.include?('-R')
+            cmd << '-X' if retain_content && !cmd.include?('-X')
           end
 
           begin
-            io = IO.popen(pager, 'w')
+            io = IO.popen(cmd, 'w')
           rescue
             next
           end

test/irb/helper.rb

@@ -93,6 +93,10 @@ def setup
       if ruby_core?
         omit "This test works only under ruby/irb"
       end
+
+      write_rc <<~RUBY
+        IRB.conf[:USE_PAGER] = false
+      RUBY
     end
 
     def teardown
@@ -197,8 +201,14 @@ def write_ruby(program)
     end
 
     def write_rc(content)
-      @irbrc = Tempfile.new('irbrc')
-      @tmpfiles << @irbrc
+      # Append irbrc content if a tempfile for it already exists
+      if @irbrc
+        @irbrc = File.open(@irbrc, "a")
+      else
+        @irbrc = Tempfile.new('irbrc')
+        @tmpfiles << @irbrc
+      end
+
       @irbrc.write(content)
       @irbrc.close
       @envs['IRBRC'] = @irbrc.path

test/irb/test_context.rb

@@ -11,6 +11,7 @@ def setup
       IRB.init_config(nil)
       IRB.conf[:USE_SINGLELINE] = false
       IRB.conf[:VERBOSE] = false
+      IRB.conf[:USE_PAGER] = false
       workspace = IRB::WorkSpace.new(Object.new)
       @context = IRB::Context.new(nil, workspace, TestInputMethod.new)
 

test/irb/test_debug_cmd.rb

@@ -346,10 +346,6 @@ def test_help_command_is_delegated_to_the_debugger
     end
 
     def test_show_cmds_display_different_content_when_debugger_is_enabled
-      write_rc <<~RUBY
-        IRB.conf[:USE_PAGER] = false
-      RUBY
-
       write_ruby <<~'ruby'
         binding.irb
       ruby

test/irb/test_irb.rb

@@ -6,10 +6,6 @@
 module TestIRB
   class InputTest < IntegrationTestCase
     def test_symbol_aliases_are_handled_correctly
-      write_rc <<~RUBY
-        IRB.conf[:USE_PAGER] = false
-      RUBY
-
       write_ruby <<~'RUBY'
         class Foo
         end
@@ -26,7 +22,6 @@ class Foo
 
     def test_symbol_aliases_are_handled_correctly_with_singleline_mode
       write_rc <<~RUBY
-        IRB.conf[:USE_PAGER] = false
         IRB.conf[:USE_SINGLELINE] = true
       RUBY
 

test/irb/yamatanooroti/test_rendering.rb

@@ -10,6 +10,8 @@
 
 class IRB::RenderingTest < Yamatanooroti::TestCase
   def setup
+    @original_term = ENV['TERM']
+    ENV['TERM'] = "xterm-256color"
     @pwd = Dir.pwd
     suffix = '%010d' % Random.rand(0..65535)
     @tmpdir = File.join(File.expand_path(Dir.tmpdir), "test_irb_#{$$}_#{suffix}")
@@ -27,6 +29,7 @@ def setup
   def teardown
     FileUtils.rm_rf(@tmpdir)
     ENV['IRBRC'] = @irbrc_backup
+    ENV['TERM'] = @original_term
     ENV.delete('RELINE_TEST_PROMPT') if ENV['RELINE_TEST_PROMPT']
   end
 
@@ -377,6 +380,40 @@ def test_pager_page_content_doesnt_page_output_when_it_fits_in_the_screen
     assert_match(/foobar/, screen)
   end
 
+  def test_long_evaluation_output_is_paged
+    write_irbrc <<~'LINES'
+      puts 'start IRB'
+      require "irb/pager"
+    LINES
+    start_terminal(10, 80, %W{ruby -I#{@pwd}/lib #{@pwd}/exe/irb}, startup_message: 'start IRB')
+    write("'a' * 80 * 11\n")
+    write("'foo' + 'bar'\n") # eval something to make sure IRB resumes
+    close
+
+    screen = result.join("\n").sub(/\n*\z/, "\n")
+    assert_match(/(a{80}\n){8}/, screen)
+    # because pager is invoked, foobar will not be evaluated
+    assert_not_match(/foobar/, screen)
+  end
+
+  def test_long_evaluation_output_is_preserved_after_paging
+    write_irbrc <<~'LINES'
+      puts 'start IRB'
+      require "irb/pager"
+    LINES
+    start_terminal(10, 80, %W{ruby -I#{@pwd}/lib #{@pwd}/exe/irb}, startup_message: 'start IRB')
+    write("'a' * 80 * 11\n")
+    write("q") # quit pager
+    write("'foo' + 'bar'\n") # eval something to make sure IRB resumes
+    close
+
+    screen = result.join("\n").sub(/\n*\z/, "\n")
+    # confirm pager has exited
+    assert_match(/foobar/, screen)
+    # confirm output is preserved
+    assert_match(/(a{80}\n){6}/, screen)
+  end
+
   def test_debug_integration_hints_debugger_commands
     write_irbrc <<~'LINES'
       IRB.conf[:USE_COLORIZE] = false