[cfe-commits] [patch] Support decltype in pseudodestructor/dependent destructor calls

[David Blaikie]

On Mon, Dec 12, 2011 at 1:10 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
> On Mon, Dec 12, 2011 at 12:25 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> On Mon, Dec 12, 2011 at 11:18 AM, Eli Friedman <eli.friedman at gmail.com> wrote:
>>> On Sun, Dec 11, 2011 at 8:27 PM, David Blaikie <dblaikie at gmail.com> wrote:
>>>> Here's the finishing touches on decltype in explicit destructor calls
>>>> - supporting pseudodestructor calls and destructor calls on dependent
>>>> types (which are handled by Clang in a similar way to pseudodestructor
>>>> calls):
>>>>
>>>> typedef int foo;
>>>> foo f;
>>>> f.~decltype(foo())();
>>>>
>>>> template<typename T>
>>>> void func(T* t) {
>>>>  t->~decltype(T())();
>>>> }
>>>>
>>>> etc...
>>>
>>> Patch looks fine.
>>
>> Thanks Eli - actually, as I was going to check this in & remembered
>> I'd wanted to refactor the arrow-testing logic I'd shamelessly
>> copy-pasted from one of the other pseudo-destructor parsing functions.
>> (it tests for arrow uses that should be '.') See
>> SemaExprCXX.cpp:4327-4345, repeated at 4445-4463, and then repeated
>> again in my patch.
>>
>> I moved this logic into a common, static, utility function - but then
>> I got thinking. How/when does this actually occur? Since
>> pseudodestructors can destroy any object, it seems impossible for us
>> to ever correctly diagnose an erroneous '->' that should be a '.'
>> before we've seen the type on the right of the '~'. So I replaced the
>> diag+fixit with an assertion & ran the test suite. It never fires.
>>
>> I tested the following for cases:
>>
>> struct foo { void bar(); };
>> void func(foo* f, foo& g) {
>>  f.~foo();
>>  f->~foo();
>>  g.~foo();
>>  g->~foo();
>> }
>>
>> and none of them produce the -> fixit:
>>
>> arrow.cpp:3:6: error: the type of object expression ('foo *') does not
>> match the type being destroyed ('foo') in pseudo-destructor
>>      expression
>>  f.~foo();
>>  ~  ^~~
>> arrow.cpp:6:4: error: member reference type 'foo' is not a pointer
>>  g->~foo();
>>  ~^
>>
>> It seems this code is dead, so far as I can tell. Should I delete the
>> existing two instances of it & remove the one I was going to add to my
>> code?
>
> Try:
>
> typedef int foo;
> void func(int x) {
>  x->~foo();
> }

Ah, indeed. Sorry I missed that - thanks for the test case. I've added
that to the existing (non-decltype) pseudodestructor tests & added
similar/more comprehensive tests for the pseudo destructor case to my
patch. See attached.

- David
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