[cfe-dev] Clang template parse problem?

[Douglas Gregor]

On Jun 6, 2012, at 7:45 AM, Thiago Adams <thiago.adams at gmail.com> wrote:

> I am having problems to compile this program using clang
> and it seems a parser bug.
> 
> clang version 3.2 (trunk)
> Target: i686-pc-win32
> Thread model: posix
> 
> (Thanks Mello for providing a updated build for windows.)
> 
> 
> Simplified code:
> 
> ----------
> #include <type_traits>
> 
> struct Property {};
> struct Property2 : public Property {};
> 
> template<class T>
> struct is_property : public std::is_base_of<Property, T> {};
> 
> template <class TA, class TB>
> auto operator > (const TA& a, const TB& b)
> -> typename std::enable_if < is_property<TA>::value ||
> is_property<TB>::value,
>            decltype(eval(a) > eval(b)) >::type
> {
>    return true;
> }
> 
> int main()
> {
>    Property2 a;
>    Property2 b;
>    if (a > b)
>      return 1;
>    return 0;
> }
> 
> ----------
> 
> error: expected ')'
> decltype(eval(a) > eval(b)) >::type
> 
> ^ points to ">"
> 
> -----------
> 
> 
> Is it a bug?

Yes, it's a Clang bug. Thanks!

> I am new to clang. Where do I report this problem?

Bug reports for Clang and LLVM should go here:

	http://llvm.org/bugs/

But, don't bother for this bug, because I went ahead and fixed this already in Clang r158111.

> The workaround is to change:
> 
> decltype(eval(a) > eval(b))

Wrapping eval(a) > eval(b) in another set of parentheses should work, too.

	- Doug