Bug#26827 - table->read_set is set incorrectly,

            causing update of a different column

Post-pushbuild fix.

bitmap_set_bit() is an inline function in DEBUG builds and
a macro in non-DEBUG builds. The latter evaluates its 'bit'
argument twice. So one must not use increment/decrement operators
on this argument.

Moved increment of pointer out of bitmap_set_bit() call.


include/my_bitmap.h:
  Bug#26827 - table->read_set is set incorrectly,
              causing update of a different column
  Added a warning comment.
sql/sql_partition.cc:
  Bug#26827 - table->read_set is set incorrectly,
              causing update of a different column
  Moved increment of pointer out of bitmap_set_bit() call.

include/my_bitmap.h

@@ -103,6 +103,17 @@ extern void bitmap_lock_invert(MY_BITMAP *map);
                                   &= ~ (1 << ((BIT) & 7)))
 #define _bitmap_is_set(MAP, BIT) (uint) (((uchar*)(MAP)->bitmap)[(BIT) / 8] \
                                          & (1 << ((BIT) & 7)))
+/*
+  WARNING!
+
+  The below symbols are inline functions in DEBUG builds and macros in
+  non-DEBUG builds. The latter evaluate their 'bit' argument twice.
+
+  NEVER use an increment/decrement operator with the 'bit' argument.
+  It would work with DEBUG builds, but fails later in production builds!
+
+  FORBIDDEN: bitmap_set_bit($my_bitmap, (field++)->field_index);
+*/
 #ifndef DBUG_OFF
 static inline void
 bitmap_set_bit(MY_BITMAP *map,uint bit)

sql/sql_partition.cc

@@ -606,8 +606,8 @@ static bool create_full_part_field_array(THD *thd, TABLE *table,
     partitioning.
   */
   if ((ptr= part_info->full_part_field_array))
-    while (*ptr)
-      bitmap_set_bit(&part_info->full_part_field_set, (*ptr++)->field_index);
+    for (; *ptr; ptr++)
+      bitmap_set_bit(&part_info->full_part_field_set, (*ptr)->field_index);
 
 end:
   DBUG_RETURN(result);