From 0e9db419beba215e97ec9f221421c89d3d2ce9ab Mon Sep 17 00:00:00 2001
From: Stan Lo <stan001212@gmail.com>
Date: Fri, 16 Feb 2024 16:12:50 +0000
Subject: [PATCH] Support repeating debugger input by passing empty input to it
 (#856)

* Test IRB's behaviour with empty input

* Handle empty input and pass it to debugger

Since `rdbg` accepts empty input to repeat the previous command, IRB
should take empty input in `irb:rdbg` sessions and pass them to the
debugger.

Currently, IRB simply ignores empty input and does nothing. This commit
creates `EmptyInput` to represent empty input so it can fit into the
current IRB's input processing flow in `Irb#eval_input`.
---
 lib/irb.rb                                    |  9 ++++---
 lib/irb/statement.rb                          | 23 ++++++++++++++++
 ...ug_cmd.rb => test_debugger_integration.rb} | 26 ++++++++++++++++++-
 test/irb/test_irb.rb                          | 18 +++++++++++++
 4 files changed, 71 insertions(+), 5 deletions(-)
 rename test/irb/{test_debug_cmd.rb => test_debugger_integration.rb} (93%)

diff --git a/lib/irb.rb b/lib/irb.rb
index 67e03f8bc..fd06626e9 100644
--- a/lib/irb.rb
+++ b/lib/irb.rb
@@ -1082,16 +1082,17 @@ def each_top_level_statement
       loop do
         code = readmultiline
         break unless code
-
-        if code != "\n"
-          yield build_statement(code), @line_no
-        end
+        yield build_statement(code), @line_no
         @line_no += code.count("\n")
       rescue RubyLex::TerminateLineInput
       end
     end
 
     def build_statement(code)
+      if code.match?(/\A\n*\z/)
+        return Statement::EmptyInput.new
+      end
+
       code.force_encoding(@context.io.encoding)
       command_or_alias, arg = code.split(/\s/, 2)
       # Transform a non-identifier alias (@, $) or keywords (next, break)
diff --git a/lib/irb/statement.rb b/lib/irb/statement.rb
index b12110600..4e17e5143 100644
--- a/lib/irb/statement.rb
+++ b/lib/irb/statement.rb
@@ -20,6 +20,29 @@ def evaluable_code
       raise NotImplementedError
     end
 
+    class EmptyInput < Statement
+      def is_assignment?
+        false
+      end
+
+      def suppresses_echo?
+        true
+      end
+
+      # Debugger takes empty input to repeat the last command
+      def should_be_handled_by_debugger?
+        true
+      end
+
+      def code
+        ""
+      end
+
+      def evaluable_code
+        code
+      end
+    end
+
     class Expression < Statement
       def initialize(code, is_assignment)
         @code = code
diff --git a/test/irb/test_debug_cmd.rb b/test/irb/test_debugger_integration.rb
similarity index 93%
rename from test/irb/test_debug_cmd.rb
rename to test/irb/test_debugger_integration.rb
index 0fb45af47..d95b01c3d 100644
--- a/test/irb/test_debug_cmd.rb
+++ b/test/irb/test_debugger_integration.rb
@@ -6,7 +6,7 @@
 require_relative "helper"
 
 module TestIRB
-  class DebugCommandTest < IntegrationTestCase
+  class DebuggerIntegrationTest < IntegrationTestCase
     def setup
       super
 
@@ -434,5 +434,29 @@ def test_multi_irb_commands_are_not_available_after_activating_the_debugger
       assert_match(/irb\(main\):001> next/, output)
       assert_include(output, "Multi-IRB commands are not available when the debugger is enabled.")
     end
+
+    def test_irb_passes_empty_input_to_debugger_to_repeat_the_last_command
+      write_ruby <<~'ruby'
+        binding.irb
+        puts "foo"
+        puts "bar"
+        puts "baz"
+      ruby
+
+      output = run_ruby_file do
+        type "next"
+        type ""
+        # Test that empty input doesn't repeat expressions
+        type "123"
+        type ""
+        type "next"
+        type ""
+        type ""
+      end
+
+      assert_include(output, "=>   2\| puts \"foo\"")
+      assert_include(output, "=>   3\| puts \"bar\"")
+      assert_include(output, "=>   4\| puts \"baz\"")
+    end
   end
 end
diff --git a/test/irb/test_irb.rb b/test/irb/test_irb.rb
index fb8b5c2bf..8c4fb5dde 100644
--- a/test/irb/test_irb.rb
+++ b/test/irb/test_irb.rb
@@ -58,6 +58,24 @@ def test_symbol_aliases_dont_affect_ruby_syntax
       assert_include output, "=> \"It's a foo\""
       assert_include output, "=> \"It's a bar\""
     end
+
+    def test_empty_input_echoing_behaviour
+      write_ruby <<~'RUBY'
+        binding.irb
+      RUBY
+
+      output = run_ruby_file do
+        type ""
+        type "  "
+        type "exit"
+      end
+
+      # Input cramped together due to how Reline's Reline::GeneralIO works
+      assert_include(
+        output,
+        "irb(main):001> irb(main):002> irb(main):002>  irb(main):002>   => nil\r\n"
+      )
+    end
   end
 
   class IrbIOConfigurationTest < TestCase