The gdb/mi command "-var-update" may return an incorrect value for "type_changed" when pretty-printers are used.

Consider the following example. The struct "printMePretty" should be pretty-printed by using the Python TestPrinter class from below. It should be printed as an integer "array" (it doesn't actually makes sense here, it's just for testing) if the structure's "printAsInt" member is true, and as a floating point "array" otherwise.


****************** File: main.cpp *****************

struct printMePretty
{
	bool printAsInt;
	int intMember;
	float floatMember;

	printMePretty() :
		printAsInt(true),
		intMember(0xFF),
		floatMember(3.1415)
	{ }
};

void main()
{
	printMePretty pretty;
	pretty.printAsInt = false;
}


****************** File: printer.py *****************

[...]

class TestPrinter:
    class _iterator:
        def __init__(self, val):
            self.val = val
            self.index = 0

        def __iter__(self):
            return self

        def next(self):
            if self.index == 1:
                raise StopIteration
            
            if self.val['printAsInt']:
                childValue = self.val['intMember']
            else:
                childValue = self.val['floatMember']
            
            self.index += 1
            return ('Value', childValue)
    
    def __init__(self, val):
        self.val = val

    def children(self):
        return self._iterator(self.val)

    def display_hint(self):
        return 'array'


****************** End of file *****************


Using Eclipse CDT to trace gdb/mi commands, one encounters the following until the line "pretty.printAsInt = false;":


-var-create --thread 1 --frame 0 - * pretty
^done,name="var1",numchild="0",value="{...}",type="printMePretty",thread-id="1",displayhint="array",dynamic="1",has_more="1"

-var-list-children var1 0 1
^done,numchild="1",displayhint="array",children=[child={name="var1.Value",exp="Value",numchild="0",type="int",thread-id="1"}],has_more="0"


OK, so "var1.Value" has type "int". Now, stepping over the line "pretty.printAsInt = false;" results in:


-var-update 1 var1
^done,changelist=[{name="var1.Value",value="3.1415",in_scope="true",type_changed="false",displayhint="array",dynamic="1",has_more="0"}]


It now says that "var1.Value" would have a "value" of "3.1415" - that's obviously a strange value for an "int" (since "type_changed" reports "false" - I suppose it should actually report that the type has changed to "float").

This seems like a bug within gdb to me. The same problem may also apply if a pretty-printer's toString() method returns gdb.Values which have different gdb.Types, depending on the data members of the structure which should be pretty-printed.