CheckBreakpoint should only stop at the first condition fulfillment line

When a condition is fulfilled (e.g. a >= 1), it usually remains true for
at least a while. However, under the current implementation, it'll stops
at every single line after the condition becomes true, which is
annoying.

So this PR introduces an extra state to make sure the BP doesn't stop
repeatedly after the condition is fulfilled.

Author: st0012

lib/debug/breakpoint.rb

@@ -326,8 +326,13 @@ def setup
         next if ThreadClient.current.management?
         next if skip_path?(tp.path)
 
-        if safe_eval tp.binding, @cond
-          suspend
+        if safe_eval(tp.binding, @cond)
+          unless fulfilled_on_current_thread?
+            set_fulfilled_on_current_thread
+            suspend
+          end
+        else
+          set_unfulfilled_on_current_thread
         end
       }
     end
@@ -337,6 +342,20 @@ def to_s
       s += super
       s
     end
+
+    private
+
+    def fulfilled_on_current_thread?
+      ThreadClient.current.check_bp_fulfilled?(self)
+    end
+
+    def set_fulfilled_on_current_thread
+      ThreadClient.current.set_check_bp_state(self, true)
+    end
+
+    def set_unfulfilled_on_current_thread
+      ThreadClient.current.set_check_bp_state(self, false)
+    end
   end
 
   class WatchIVarBreakpoint < Breakpoint

lib/debug/thread_client.rb

@@ -95,6 +95,8 @@ def initialize id, q_evt, q_cmd, thr = Thread.current
       @obj_map = {} # { object_id => obj } for CDP
       @recorder = nil
       @mode = :waiting
+      # every thread should maintain its own CheckBreakpoint fulfillment state
+      @check_bp_fulfillment_map = {} # { check_bp => boolean }
       set_mode :running
       thr.instance_variable_set(:@__thread_client_id, id)
 
@@ -337,6 +339,14 @@ def step_tp iter, events = [:line, :b_return, :return]
       end
     end
 
+    def set_check_bp_state(bp, state)
+      @check_bp_fulfillment_map[bp] = state
+    end
+
+    def check_bp_fulfilled?(bp)
+      @check_bp_fulfillment_map[bp]
+    end
+
     ## cmd helpers
 
     if TracePoint.respond_to? :allow_reentry

test/debug/break_test.rb

@@ -645,8 +645,11 @@ def program
      2| a += 1
      3| a += 2
      4| a += 3
-     5|
-     6| binding.b
+     5| a = 0
+     6| a = 1
+     7| a = 2
+     8| a = 3
+     9| binding.b
       RUBY
     end
 
@@ -671,6 +674,22 @@ def test_conditional_breakpoint_shows_error
       end
     end
 
+    def test_conditional_breakpoint_ignores_unchanged_true_condition
+      debug_code(program) do
+        type 'break if: a > 0'
+        type 'c'
+        assert_line_num(2) # stopped by line 1
+        # the state remains fulfilled so the next 2 lines don't trigger stoppage
+        type 'c'
+        # line 5 changes the state. so the next true condition will stop the program again
+        assert_line_num(7) # stopped by line 6
+        type 'c'
+        # the state remains fulfilled again, so the line 7 doesn't trigger stoppage
+        assert_line_num(9)
+        type 'c'
+      end
+    end
+
     class PathOptionTest < TestCase
       def extra_file
         <<~RUBY
@@ -712,10 +731,6 @@ def test_the_path_option_supersede_skip_path_config
             assert_line_num(3)
             assert_line_text(/201/)
             type 'c'
-            # this stop is because check bp stops at every line after the condition is fulfilled, which is another issue
-            # see https://github.com/ruby/debug/issues/406 for more about the issue
-            assert_line_num(4)
-            type 'c'
           end
         end