OLEAUT32: bug 4502 - request for comment before trying to fix

[Alex Villací­s Lasso]

I would like to draw attention to bug 4502. This bug can cause any VB 
application to crash when the DatePicker control is used, and an attempt 
is made to assign a date value in VB code. Even though I found this bug 
while testing an application I wrote, this might not be specific to this 
application. It is only recently that I have some time to dedicate to 
this bug, but I would like somebody to comment on this.

When the sample application is run with WINEDEBUG=ole,variant, the 
failing invocation looks like this:

trace:ole:ITypeInfo_fnInvoke 
(0x7fdd5440)(0x7fd9f61c,id=20,flags=0x00000004,0x7fa3ee8c,(nil),0x7fa3ee6c,0x7fa3ee9c)
trace:ole:dump_DispParms args=1 named args=1
trace:ole:dump_Variant 0x7fa3eef4->{VT_DATE(38788,0x7fa3ec7c)
trace:variant:VarUdateFromDate (38788,0x00000000,0x7fa3ec36)
trace:ole:dump_Variant ,2006/03/12 00:00:00}
trace:ole:ITypeInfo_fnInvoke invoking:
L"Value"(1)
    parm0: L"Value"
memid is 00000014
Param 0:
        tdesc.vartype 12 (VT_VARIANT)
        u.paramdesc.wParamFlags PARAMFLAG_FIN
        u.paramdesc.lpex (nil)
    funckind: 1 (pure virtual)
    invkind: 4 (property put)
    callconv: 4 (stdcall)
    oVft: 224
    cParamsOpt: 0
    wFlags: 3c
    elemdescFunc (return value type):
        tdesc.vartype 25 (VT_HRESULT)
        u.paramdesc.wParamFlags PARAMFLAGS_NONE
        u.paramdesc.lpex (nil)
    helpstring: L"Returns/sets the current date."
    entry: (null)
trace:ole:ITypeInfo_fnInvoke changing args
trace:ole:dump_Variant 0x7fa3eef4->{VT_DATE(38788,0x7fa3ec7c)
trace:variant:VarUdateFromDate (38788,0x00000000,0x7fa3ec36)
trace:ole:dump_Variant ,2006/03/12 00:00:00}
trace:variant:VariantChangeTypeEx 
(0x7fdd5520->(VT_DATE),0x7fa3eef4->(VT_DATE),0x00000400,0x0000,VT_VARIANT)
trace:variant:VariantClear (0x7fa3ec40->(VT_EMPTY))
trace:variant:VariantClear (0x7fa3ec30->(VT_EMPTY))
trace:variant:VariantCopyInd (0x7fa3ec30->(VT_EMPTY),0x7fa3eef4->(VT_DATE))
trace:variant:VariantCopy (0x7fa3ec30->(VT_EMPTY),0x7fa3eef4->(VT_DATE))
trace:variant:VariantClear (0x7fa3ec30->(VT_EMPTY))
trace:variant:VARIANT_Coerce 
(0x7fa3ec40->(VT_EMPTY),0x00000400,0x0000,0x7fa3ec30->(VT_DATE),VT_VARIANT)
trace:variant:VariantClear (0x7fa3ec40->(VT_EMPTY))
trace:variant:VariantClear (0x7fa3ec30->(VT_DATE))
trace:variant:VariantChangeTypeEx returning 0x80020005, 
0x7fdd5520->(VT_DATE)
err:ole:ITypeInfo_fnInvoke failed to convert param 0 to VT_VARIANT from 
VT_DATE
trace:ole:ITypeInfo_fnInvoke -- 0x80020005

The Property Put seems to be declared as taking one VT_VARIANT 
parameter, and the VB code supplies a VT_DATE value. Therefore, an 
attempt is made to coerce VT_DATE --> VT_VARIANT. However, 
VariantChangeTypeEx() does not support conversion of *any* kind of 
variant into VT_VARIANT, so the call fails, and this brings down the 
application. I was on half a mind to add the VT_VARIANT conversion to 
VariantChangeTypeEx() myself, but then I checked the tests for this 
operation, and it seems that the absence of support for VT_VARIANT is 
actually expected (unless I am misreading the code). Therefore, one of 
the following two things is happening:

1) There is some error in the reading of the typelib, since a Property 
Put should not have a VT_VARIANT parameter in the first place.
2) ITypeInfo::Invoke should do the VT_VARIANT conversion itself, 
precisely because VariantChangeTypeEx() won't do it.

I am inclined to the second option, but I want to hear some comment 
before attempting to create a patch.

Alex Villacís Lasso