*.idl: Use correct type for BSTR strings in the defaultvalue() statements.

Dmitry Timoshkov dmitry at baikal.ru
Fri Nov 6 07:33:34 CST 2015

Jacek Caban <jacek at codeweavers.com> wrote:

> > I don't really follow your objections. It's pretty clear that Wine .idl
> > files with defaultvalue("") statements for BSTR type are broken. There
> > are two ways to fix them:
> > 1) fix .idl files, widl and midl already have proper support for L"" syntax.
> > 2) don't fix .idl files (just because PSDK has them that way) and add magic
> > handling for BSTR to widl.
> > Fixing .idl files is a natural and easy fix, what syntax uses PSDK doesn't
> > matter al all, it's even better to differ from PSDK headers in this case.
> Well, out of those two options I'd prefer option 1. That's a real bug.
> Option 2 just changes IDLs that are perfectly fine, just misinterpreted
> by widl.
> FWIW think that it's all broken really badly by Microsoft. BSTR strings
> are supposed to be allocated by SysAllocString* allocators and can't be
> static strings. It will fail as soon as someone tries things like
> SysStringLen() call on it. What midl does is promoting broken use of
> BSTR type.

Yes, BSTRs are length-prefixed WCHAR strings, but BSTR and WCHAR* are often
freely interchanged in the APIs, and that's not our fault.

> But, well, we should follow that for compatibility :/

Not the first time :)

> >>>> > > > Generated headers should use L"", like you said. But only in
> >>>> > > > case of empty strings.
> >>> > >
> >>> > > midl always generates L"" syntax, regardless whether it's an empty string
> >>> > > or not.
> >> > 
> >> > 
> >> > I don't see this in mshtml.h when default value is not an empty string.
> > Probably midl doesn't correctly handle even the magic that it's supposed to
> > support. That just confirms that adding "magic" support for defaultvalue()
> > to widl wouldn't solve the problem completely, and support for this "magic"
> > would need adding even more magic to match midl brokeness.
> You both seem to misinterpret what's heppening with mshtm.idl. C++
> default values can be emitted only for last arguments. There may be a
> few of them, but they can't be followed by an argument without a default
> value. That's why midl doesn't emit default values for non-empty strings
> found in mshtml.idl. I checked that with tests and midl emits L"..."
> strings as expected.

Thanks for explaining Jacek, much appreciated.


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