BUG#11765644: DEBUG 'D' LIST SHOULD STAY EMPTY AFTER SET

              DEBUG="+D,<SYMBOL>"
PROBLEM AND FIX:
When the debug 'd' flag has been set to empty, then all
DBUG_ macros are enabled. But if one then sets debug="
+d,foo" then only foo, all others are turned off. The
expected/intended behaviour should be to add debug for
'symbol' in addition to whatever was enabled before.
The fix adds keyword to the stack of active keyword list
if debug was not enabled for all symbols. Also turn debug
off if the last keyword is removed from the stack of
keywords. NOTE: This shall require a change in the docs
to reflect the changed behaviour in this bug

Author: thayumanavar77

dbug/dbug.c

@@ -598,19 +598,37 @@ int DbugParse(CODE_STATE *cs, const char *control)
         if (!is_shared(stack, keywords))
           FreeList(stack->keywords);
         stack->keywords=NULL;
-        stack->flags &= ~DEBUG_ON;
+        stack->flags&= ~DEBUG_ON;
         break;
       }
       if (rel && is_shared(stack, keywords))
         stack->keywords= ListCopy(stack->keywords);
       if (sign < 0)
       {
         if (DEBUGGING)
+        {
           stack->keywords= ListDel(stack->keywords, control, end);
-      break;
+          /* Turn off DEBUG_ON if it is last keyword to be removed. */
+          if (stack->keywords == NULL)
+            stack->flags&= ~DEBUG_ON;
+        }
+        break;
       }
-      stack->keywords= ListAdd(stack->keywords, control, end);
-      stack->flags |= DEBUG_ON;
+
+      /* Do not add keyword if debugging all is enabled. */
+      if (!(DEBUGGING && stack->keywords == NULL))
+      {
+        stack->keywords= ListAdd(stack->keywords, control, end);
+        stack->flags|= DEBUG_ON;
+      }
+
+      /* If debug all is enabled, make the keyword list empty. */
+      if (sign == 1 && control == end)
+      {
+        FreeList(stack->keywords);
+        stack->keywords= NULL;
+      }
+
       break;
     case 'D':
       stack->delay= atoi(control);

unittest/gunit/dbug-t.cc

@@ -98,5 +98,62 @@ TEST(DebugPrintDeathTest, PrintEval)
   EXPECT_DEATH_IF_SUPPORTED(DBUG_PRINT("never",("%d",1/y)), "");
   DBUG_SET("");
 }
+
+
+TEST(DebugSetTest, DebugKeywordsTest)
+{
+  char buf[1024];
+
+  /*
+    Enable d flag, then enable debug on a keyword. The debug should
+    remain set to d and empty list of keywords indicating debug is
+    enabled for all.
+  */
+  DBUG_SET("d");
+  DBUG_SET("+d,keyword");
+  DBUG_EXPLAIN(buf, sizeof(buf));
+  EXPECT_STREQ("d", buf);
+  DBUG_SET("");
+
+  /*
+    Set debug on a specific keyword. Debug should be enabled
+    for the keyword.
+  */
+  DBUG_SET("+d,keyword");
+  DBUG_EXPLAIN(buf, sizeof(buf));
+  EXPECT_STREQ("d,keyword", buf);
+
+  /*
+    Remove the keyword from debug list. Debug should be
+    disabled.
+  */
+  DBUG_SET("-d,keyword");
+  DBUG_EXPLAIN(buf, sizeof(buf));
+  EXPECT_STREQ("",buf);
+  DBUG_SET("");
+
+  /*
+    Enable debug for a keyword. Then enable debug for all
+    keywords. Debug should now be enabled for all keywords.
+  */
+  DBUG_SET("+d,keyword");
+  DBUG_SET("+d");
+  DBUG_EXPLAIN(buf,sizeof(buf));
+  EXPECT_STREQ("d",buf);
+  DBUG_SET("");
+
+  // Add multiple debug keywords.
+  DBUG_SET("+d,keyword1");
+  DBUG_SET("+d,keyword2");
+  DBUG_EXPLAIN(buf,sizeof(buf));
+  EXPECT_STREQ("d,keyword1,keyword2",buf);
+  DBUG_SET("-d,keyword1");
+  DBUG_EXPLAIN(buf,sizeof(buf));
+  EXPECT_STREQ("d,keyword2",buf);
+  DBUG_SET("-d,keyword2");
+  DBUG_EXPLAIN(buf,sizeof(buf));
+  EXPECT_STREQ("",buf);
+  DBUG_SET("");
+}
 #endif /* DBUG_OFF */
 }