use rb_profile_frames for frame_depth

Author: WillHalto

ext/debug/debug.c

@@ -89,12 +89,24 @@ capture_frames(VALUE self, VALUE skip_path_prefix)
     return rb_debug_inspector_open(di_body, (void *)skip_path_prefix);
 }
 
+#define BUFF_SIZE 4096
+
 static VALUE
 frame_depth(VALUE self)
 {
-    // TODO: more efficient API
-    VALUE bt = rb_make_backtrace();
-    return INT2FIX(RARRAY_LEN(bt));
+    int size = rb_profile_frames(0, BUFF_SIZE, buff, lines);
+
+    // If the buffer is full, there might be more frames.
+    // Fall back to rb_make_backtrace to get them all.
+    if (size >= BUFF_SIZE) {
+        VALUE bt = rb_make_backtrace();
+        size = RARRAY_LEN(bt);
+    } 
+ 
+    return INT2FIX(size);
 }
 
 // iseq

test/console/control_flow_commands_test.rb

@@ -358,4 +358,54 @@ def test_next_steps_over_rescue_when_raising_from_method
       end
     end
   end
+
+  #
+  # Tests that next/finish work for a deep call stack.
+  # We use different logic for computing frame depth when the call stack is above/below 4096.
+  #
+  class DeepCallstackTest < ConsoleTestCase
+    def program
+      <<~RUBY
+         1| # target.rb
+         2| def foo
+         3|     "hello"
+         4| end
+         5|   
+         6| def recursive(n,stop)
+         7|   foo
+         8|   return if n >= stop
+         9| 
+        10|   recursive(n + 1, stop)
+        11| end
+        12| 
+        13| recursive(0, 4100)
+        14| 
+        15| "done"
+      RUBY
+    end
+    
+    def test_next
+      debug_code(program) do
+        type 'b 13'
+        type 'c'
+        assert_line_num 13
+        type 'n'
+        assert_line_num 15
+        type 'q!'
+      end
+    end
+
+    def test_finish
+      debug_code(program) do
+        type 'b 13'
+        type 'c'
+        assert_line_num 13
+        type 's'
+        assert_line_num 7
+        type 'fin'
+        assert_line_num 11
+        type 'q!'
+      end
+    end
+  end
 end