From 8e9f4ee17b783caa8151f217f69b72fe9c950dd4 Mon Sep 17 00:00:00 2001
From: Stan Lo <stan001212@gmail.com>
Date: Tue, 18 Jul 2023 17:35:12 +0100
Subject: [PATCH] Prevent using multi-irb and activating debugger at the same
 time

Multi-irb makes a few assumptions:

- IRB will manage all threads that host sub-irb sessions
- All IRB sessions will be run on the threads created by IRB itself

However, when using the debugger these assumptions are broken:

- `debug` will freeze ALL threads when it suspends the session (e.g. when
  hitting a breakpoint, or performing step-debugging).
- Since the irb-debug integration runs IRB as the debugger's interface,
  it will be run on the debugger's thread, which is not managed by IRB.

So we should prevent the 2 features from being used at the same time.
To do that, we check if the other feature is already activated when
executing the commands that would activate the other feature.
---
 lib/irb/cmd/debug.rb       |  5 +++++
 lib/irb/cmd/subirb.rb      | 36 ++++++++++++++++++++++++++++++++++--
 test/irb/test_debug_cmd.rb | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/lib/irb/cmd/debug.rb b/lib/irb/cmd/debug.rb
index 01bbf49d5..9eca96421 100644
--- a/lib/irb/cmd/debug.rb
+++ b/lib/irb/cmd/debug.rb
@@ -35,6 +35,11 @@ def execute(pre_cmds: nil, do_cmds: nil)
             return
           end
 
+          if IRB.respond_to?(:JobManager)
+            warn "Can't start the debugger when IRB is running in a multi-IRB session."
+            return
+          end
+
           unless IRB::Debug.setup(irb_context.irb)
             puts <<~MSG
               You need to install the debug gem before using this command.
diff --git a/lib/irb/cmd/subirb.rb b/lib/irb/cmd/subirb.rb
index 3018ab277..5ffd64641 100644
--- a/lib/irb/cmd/subirb.rb
+++ b/lib/irb/cmd/subirb.rb
@@ -11,8 +11,7 @@ module IRB
 
   module ExtendCommand
     class MultiIRBCommand < Nop
-      def initialize(conf)
-        super
+      def execute(*args)
         extend_irb_context
       end
 
@@ -29,6 +28,10 @@ def extend_irb_context
         # this extension patches IRB context like IRB.CurrentContext
         require_relative "../ext/multi-irb"
       end
+
+      def print_debugger_warning
+        warn "Multi-IRB commands are not available when the debugger is enabled."
+      end
     end
 
     class IrbCommand < MultiIRBCommand
@@ -37,6 +40,13 @@ class IrbCommand < MultiIRBCommand
 
       def execute(*obj)
         print_deprecated_warning
+
+        if irb_context.with_debugger
+          print_debugger_warning
+          return
+        end
+
+        super
         IRB.irb(nil, *obj)
       end
     end
@@ -47,6 +57,13 @@ class Jobs < MultiIRBCommand
 
       def execute
         print_deprecated_warning
+
+        if irb_context.with_debugger
+          print_debugger_warning
+          return
+        end
+
+        super
         IRB.JobManager
       end
     end
@@ -57,6 +74,14 @@ class Foreground < MultiIRBCommand
 
       def execute(key = nil)
         print_deprecated_warning
+
+        if irb_context.with_debugger
+          print_debugger_warning
+          return
+        end
+
+        super
+
         raise CommandArgumentError.new("Please specify the id of target IRB job (listed in the `jobs` command).") unless key
         IRB.JobManager.switch(key)
       end
@@ -68,6 +93,13 @@ class Kill < MultiIRBCommand
 
       def execute(*keys)
         print_deprecated_warning
+
+        if irb_context.with_debugger
+          print_debugger_warning
+          return
+        end
+
+        super
         IRB.JobManager.kill(*keys)
       end
     end
diff --git a/test/irb/test_debug_cmd.rb b/test/irb/test_debug_cmd.rb
index 90b19e52d..01546ba6c 100644
--- a/test/irb/test_debug_cmd.rb
+++ b/test/irb/test_debug_cmd.rb
@@ -356,5 +356,37 @@ def bar
       assert_match(/irb\(main\):001:0> next/, output)
       assert_include(output, "InputMethod: RelineInputMethod")
     end
+
+    def test_debugger_cant_be_activated_while_multi_irb_is_active
+      write_ruby <<~'ruby'
+        binding.irb
+        a = 1
+      ruby
+
+      output = run_ruby_file do
+        type "jobs"
+        type "next"
+        type "exit"
+      end
+
+      assert_match(/irb\(main\):001:0> jobs/, output)
+      assert_include(output, "Can't start the debugger when IRB is running in a multi-IRB session.")
+    end
+
+    def test_multi_irb_commands_are_not_available_after_activating_the_debugger
+      write_ruby <<~'ruby'
+        binding.irb
+        a = 1
+      ruby
+
+      output = run_ruby_file do
+        type "next"
+        type "jobs"
+        type "continue"
+      end
+
+      assert_match(/irb\(main\):001:0> next/, output)
+      assert_include(output, "Multi-IRB commands are not available when the debugger is enabled.")
+    end
   end
 end