[PATCH] Fix for Bug 15290 - Segmentation fault during template instantiation

[Ismail Pazarbasi]

On Fri, Feb 22, 2013 at 12:18 AM, Richard Smith <richard at metafoo.co.uk> wrote:
> On Thu, Feb 21, 2013 at 3:11 PM, Ismail Pazarbasi
> <ismail.pazarbasi at gmail.com> wrote:
>>
>> On Thu, Feb 21, 2013 at 11:34 PM, Richard Smith <richard at metafoo.co.uk>
>> wrote:
>> > Hi!
>> >
>> > On Thu, Feb 21, 2013 at 1:53 PM, Ismail Pazarbasi
>> > <ismail.pazarbasi at gmail.com> wrote:
>> >>
>> >> Hi,
>> >>
>> >> when operand of a noexcept operator in a friend function definition
>> >> involves a member of a template class enclosing the friend definition,
>> >> Clang casts current context to either a CXXMethodDecl or a
>> >> CXXRecordDecl. Since friend function is neither of these, cast fails.
>> >> The same test in a non-template class works fine.
>> >>
>> >> The first patch tries to retrieve the lexical parent of the function
>> >> definition (per class.friend/p6-7), which is expected to be a record
>> >> type. A test is also provided (also, pasting below for reference).
>> >>
>> >> template<typename T>
>> >> class noexcept_member_operand_at_friend_definition {
>> >>   T v_;
>> >>   friend int add_to_v(noexcept_member_operand_at_friend_definition &t)
>> >> noexcept(noexcept(v_ + 42))
>> >>   {
>> >>     return t.v_ + 42;
>> >>   }
>> >> };
>> >>
>> >> void this_expr()
>> >> {
>> >>   noexcept_member_operand_at_friend_definition<int> t;
>> >>   add_to_v(t);
>> >> }
>> >
>> >
>> > Thanks for looking into this. There is a more fundamental problem here,
>> > which this patch is masking rather than fixing. Per 5.1.1/3, 'this' is
>> > not
>> > permitted to appear in the declaration of a friend function, so per
>> > 9.3.1/3,
>> > we should not transform the mention of 'v_' into a class member access.
>> > Therefore, we should build a DeclRefExpr for the member, not a
>> > CXXMemberExpr, in this case. It looks like the bug is that
>> > Parser::ParseFunctionDeclarator's IsCXX11MemberFunction is not taking
>> > 'friend' into account when determining whether a function in a class is
>> > a
>> > member function.
>> >
>> > To demonstrate the difference, here's a testcase which we should reject,
>> > but
>> > we currently accept (and still accept with your patch):
>> >
>> > struct S {
>> >   friend auto f() -> decltype(this);
>> > };
>> Thank you for reviewing these.
>>
>> I first thought we should have rejected this and the case with a
>> non-template class as well. But both GCC and Clang accepted, and I
>> honestly started to look what am I missing. I found class.friend/p6-7,
>> which has nothing to do with 'this' pointer, but only lexical scope;
>> so I thought name lookup can find identifier in the class' scope, and
>> because 'this' is not used inside the function definition itself, it
>> might be legal to use 'this' inside noexcept operator (which is
>> clearly not permitted by 5.1.1/3).
>
>
> Your example is valid. While you can't use 'this' in a friend declaration,
> you *can* use 'v_', because noexcept is an unevaluated context; see
> 5.1.1/13.

OK, thank you very much, I think I understood it. I will check what
can I do about IsCXX11MemberFunction function first.

>>
>> >
>> >> The second patch is a minor one; it merges two if statements that have
>> >> the same condition.
>> >
>> >
>> > I don't think this patch is correct. Note that the body of the first
>> > 'if'
>> > statement can cause the condition of the second to no longer be 'true'.
>> Yes, you are right!
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>
>