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

[Richard Smith]

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);
};

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'.
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