Allow reentrant breakpoint on Ruby 3.1

lib/debug/breakpoint.rb

@@ -327,6 +327,7 @@ def initialize expr, path
 
     def setup
       @tp = TracePoint.new(:line){|tp|
+        next if SESSION.in_subsession? # TODO: Ractor support
         next if ThreadClient.current.management?
         next if skip_path?(tp.path)
 
@@ -375,7 +376,6 @@ def watch_eval(tp)
 
     def setup
       @tp = TracePoint.new(:line, :return, :b_return){|tp|
-
         watch_eval(tp)
       }
     end

lib/debug/session.rb

@@ -105,7 +105,7 @@ def initialize ui
       @intercept_trap_sigint = false
       @intercepted_sigint_cmd = 'DEFAULT'
       @process_group = ProcessGroup.new
-      @subsession = nil
+      @subsession_stack = []
 
       @frame_map = {} # for DAP: {id => [threadId, frame_depth]} and CDP: {id => frame_depth}
       @var_map   = {1 => [:globals], } # {id => ...} for DAP
@@ -216,6 +216,7 @@ def process_event evt
         q << true
 
       when :init
+        enter_subsession
         wait_command_loop tc
 
       when :load
@@ -258,7 +259,7 @@ def process_event evt
         end
 
       when :result
-        raise "[BUG] not in subsession" unless @subsession
+        raise "[BUG] not in subsession" if @subsession_stack.empty?
 
         case ev_args.first
         when :try_display
@@ -1540,27 +1541,38 @@ def get_thread_client th = Thread.current
     end
 
     private def enter_subsession
-      raise "already in subsession" if @subsession
-      @subsession = true
-      stop_all_threads
-      @process_group.lock
-      DEBUGGER__.info "enter_subsession"
+      if !@subsession_stack.empty?
+        DEBUGGER__.info "Enter subsession (nested #{@subsession_stack.size})"
+      else
+        DEBUGGER__.info "Enter subsession"
+        stop_all_threads
+        @process_group.lock
+      end
+
+      @subsession_stack << true
     end
 
     private def leave_subsession type
-      DEBUGGER__.info "leave_subsession"
-      @process_group.unlock
-      restart_all_threads
+      raise '[BUG] leave_subsession: not entered' if @subsession_stack.empty?
+      @subsession_stack.pop
+
+      if @subsession_stack.empty?
+        DEBUGGER__.info "Leave subsession"
+        @process_group.unlock
+        restart_all_threads
+      else
+        DEBUGGER__.info "Leave subsession (nested #{@subsession_stack.size})"
+      end
+
       @tc << type if type
       @tc = nil
-      @subsession = false
     rescue Exception => e
-      STDERR.puts [e, e.backtrace].inspect
+      STDERR.puts PP.pp([e, e.backtrace], ''.dup)
       raise
     end
 
     def in_subsession?
-      @subsession
+      !@subsession_stack.empty?
     end
 
     ## event

lib/debug/thread_client.rb

@@ -346,9 +346,39 @@ def step_tp iter, events = [:line, :b_return, :return]
 
     ## cmd helpers
 
-    # this method is extracted to hide frame_eval's local variables from C method eval's binding
-    def instance_eval_for_cmethod frame_self, src
-      frame_self.instance_eval(src)
+    if TracePoint.respond_to? :allow_reentry
+      def tp_allow_reentry
+        TracePoint.allow_reentry do
+          yield
+        end
+      rescue RuntimeError => e
+        # on the postmortem mode, it is not stopped in TracePoint
+        if e.message == 'No need to allow reentrance.'
+          yield
+        else
+          raise
+        end
+      end
+    else
+      def tp_allow_reentry
+        yield
+      end
+    end
+
+    def frame_eval_core src, b
+      if b
+        f, _l = b.source_location
+
+        tp_allow_reentry do
+          b.eval(src, "(rdbg)/#{f}")
+        end
+      else
+        frame_self = current_frame.self
+
+        tp_allow_reentry do
+          frame_self.instance_eval(src)
+        end
+      end
     end
 
     SPECIAL_LOCAL_VARS = [
@@ -365,16 +395,13 @@ def frame_eval src, re_raise: false
         b.local_variable_set(name, var) if /\%/ !~ name
       end
 
-      result = if b
-                  f, _l = b.source_location
-                  b.eval(src, "(rdbg)/#{f}")
-                else
-                  frame_self = current_frame.self
-                  instance_eval_for_cmethod(frame_self, src)
-                end
+      result = frame_eval_core(src, b)
+
       @success_last_eval = true
       result
 
+    rescue SystemExit
+      raise
     rescue Exception => e
       return yield(e) if block_given?