Bug #34883 ft_boolean_syntax cant be assigned from user variable to global var.

Description:
When you finally assign temporary initial variable's value to session value, an error occurs that '' value cannot be set to variable

How to repeat:
Sample Code: 
SELECT @global_start_value;
--Error ER_WRONG_VALUE_FOR_VAR
SET @@global.ft_boolean_syntax = @global_start_value;

Actual Result: 
SELECT @global_start_value;
@global_start_value
+ -><()~*:""&|
SET @@global.ft_boolean_syntax = @global_start_value;
ERROR 42000: Variable 'ft_boolean_syntax' can't be set to the value of ''

Thank you for a bug report. Other variables, e.g. @@global.key_buffer_size, can be set this way, so it looks like inconsistency.

The manual specifies what values are allowed for ft_boolean_syntax. Empty string is not one of them.

And this has nothing to do with temporary variables.

So it means that we can not assign temporary variable to ft_boolean_syntax even if the variable contains the valid value.

SET @global_start_value = @@global.ft_boolean_syntax;
SELECT @global_start_value;
@global_start_value
+ -><()~*:""&|
SET @@global.ft_boolean_syntax = @global_start_value;
ERROR 42000: Variable 'ft_boolean_syntax' can't be set to the value of ''

As we can see that @global_start_value contains valid value but assigning this  variable is causing the problem.

You're right, sorry for confusion.

Hint: the code uses var->value->str_value.c_ptr(), it should use var->value->val_str() for an obvious reason. this was copy-pasted all over set_var.cc, all places should be fixed.

workaround: set the value of the via program code

will be fixed in WL#4738

Pushed into 5.5.3-m3 (revid:alik@sun.com-20100306103849-hha31z2enhh7jwt3) (version source revid:vvaintroub@fedora12-20091225154921-x25a5pyw1pxiwobv) (merge vers: 5.5.99) (pib:16)

Noted in 5.5.3 changelog.

String-valued system variables could be assigned literal values, but
could not be assigned values using expressions. Now expressions are
legal.