7 files changed, 65 insertions, 17 deletions

diff --git a/dbug/dbug.c b/dbug/dbug.c
index 7f4292d18b1..666ab2b3e3c 100644
--- a/dbug/dbug.c
+++ b/dbug/dbug.c
@@ -412,15 +412,11 @@ void _db_process_(const char *name)
   cs->process= name;
 }
 
+
 /*
  *  FUNCTION
  *
- *      _db_set_       set current debugger settings
- *
- *  SYNOPSIS
- *
- *      VOID _db_set_(control)
- *      char *control;
+ *      DbugParse       parse control string and set current debugger setting
  *
  *  DESCRIPTION
  *
@@ -444,7 +440,7 @@ void _db_process_(const char *name)
  *
  */
 
-void _db_set_(CODE_STATE *cs, const char *control)
+static void DbugParse(CODE_STATE *cs, const char *control)
 {
   const char *end;
   int rel=0;
@@ -674,6 +670,35 @@ void _db_set_(CODE_STATE *cs, const char *control)
 /*
  *  FUNCTION
  *
+ *      _db_set_       set current debugger settings
+ *
+ *  SYNOPSIS
+ *
+ *      VOID _db_set_(control)
+ *      char *control;
+ *
+ *  DESCRIPTION
+ *
+ *      Given pointer to a debug control string in "control",
+ *      parses the control string, and sets up a current debug
+ *      settings. Pushes a new debug settings if the current is
+ *      set to the initial debugger settings.
+ */
+
+void _db_set_(CODE_STATE *cs, const char *control)
+{
+  get_code_state_or_return;
+
+  if (cs->stack == &init_settings)
+    PushState(cs);
+
+  DbugParse(cs, control);
+}
+
+
+/*
+ *  FUNCTION
+ *
  *      _db_push_       push current debugger settings and set up new one
  *
  *  SYNOPSIS
@@ -685,7 +710,7 @@ void _db_set_(CODE_STATE *cs, const char *control)
  *
  *      Given pointer to a debug control string in "control", pushes
  *      the current debug settings, parses the control string, and sets
- *      up a new debug settings with _db_set_()
+ *      up a new debug settings with DbugParse()
  *
  */
 
@@ -694,7 +719,7 @@ void _db_push_(const char *control)
   CODE_STATE *cs=0;
   get_code_state_or_return;
   PushState(cs);
-  _db_set_(cs, control);
+  DbugParse(cs, control);
 }
 
 /*
@@ -717,7 +742,7 @@ void _db_set_init_(const char *control)
   CODE_STATE tmp_cs;
   bzero((uchar*) &tmp_cs, sizeof(tmp_cs));
   tmp_cs.stack= &init_settings;
-  _db_set_(&tmp_cs, control);
+  DbugParse(&tmp_cs, control);
 }
 
 /*
diff --git a/dbug/user.r b/dbug/user.r
index e41367de321..19de840d0ad 100644
--- a/dbug/user.r
+++ b/dbug/user.r
@@ -730,8 +730,9 @@ warning will be given.  The DBUG_POP macro has no arguments.
 EX:\ \fCDBUG_POP\ ();\fR
 .SP 1
 .LI DBUG_SET\ 
-Modifies the current debugger state on top of the stack using the
-debug control string passed as the macro argument.  Unless
+Modifies the current debugger state on top of the stack or pushes
+a new state if the current is set to the initial settings, using
+the debug control string passed as the macro argument.  Unless
 .I incremental
 control string is used (see below), it's equivalent to a combination of
 DBUG_POP and DBUG_PUSH.
diff --git a/mysql-test/r/variables_debug.result b/mysql-test/r/variables_debug.result
new file mode 100644
index 00000000000..9cd133dddb1
--- /dev/null
+++ b/mysql-test/r/variables_debug.result
@@ -0,0 +1,12 @@
+set debug= 'T';
+select @@debug;
+@@debug
+T
+set debug= '+P';
+select @@debug;
+@@debug
+P:T
+set debug= '-P';
+select @@debug;
+@@debug
+T
diff --git a/mysql-test/t/disabled.def b/mysql-test/t/disabled.def
index 670a9c6a755..9309d668a15 100644
--- a/mysql-test/t/disabled.def
+++ b/mysql-test/t/disabled.def
@@ -22,4 +22,3 @@ wait_timeout         : Bug#32801 wait_timeout.test fails randomly
 ctype_create         : Bug#32965 main.ctype_create fails
 status               : Bug#32966 main.status fails
 ps_ddl               : Bug#12093 2007-12-14 pending WL#4165 / WL#4166
-query_cache_debug    : Bug#34424: query_cache_debug.test leads to valgrind warnings
diff --git a/mysql-test/t/variables_debug.test b/mysql-test/t/variables_debug.test
new file mode 100644
index 00000000000..7dcaf246803
--- /dev/null
+++ b/mysql-test/t/variables_debug.test
@@ -0,0 +1,12 @@
+--source include/have_debug.inc
+
+#
+# Bug#34678 @@debug variable's incremental mode
+#
+
+set debug= 'T';
+select @@debug;
+set debug= '+P';
+select @@debug;
+set debug= '-P';
+select @@debug;
diff --git a/mysys/my_thr_init.c b/mysys/my_thr_init.c
index 1ba6e5ac92d..933674fa007 100644
--- a/mysys/my_thr_init.c
+++ b/mysys/my_thr_init.c
@@ -332,6 +332,7 @@ void my_thread_end(void)
     /* tmp->dbug is allocated inside DBUG library */
     if (tmp->dbug)
     {
+      DBUG_POP();
       free(tmp->dbug);
       tmp->dbug=0;
     }
diff --git a/sql/set_var.cc b/sql/set_var.cc
index 4c77cbfff82..64c79ed3bb3 100644
--- a/sql/set_var.cc
+++ b/sql/set_var.cc
@@ -3926,10 +3926,8 @@ bool sys_var_thd_dbug::update(THD *thd, set_var *var)
   if (var->type == OPT_GLOBAL)
     DBUG_SET_INITIAL(var ? var->value->str_value.c_ptr() : "");
   else
-  {
-    DBUG_POP();
-    DBUG_PUSH(var ? var->value->str_value.c_ptr() : "");
-  }
+    DBUG_SET(var ? var->value->str_value.c_ptr() : "");
+
   return 0;
 }