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Re: [PATCH] PR c++/26693

Jason Merrill a Ãcrit :
Dodji Seketeli wrote:
2/ When tsubst() encounters a typedef variant type, it tries to "reuse" its specialization, instead of tsubst-ing its main variant type. This works great. But when the main variant type is a TYPENAME_TYPE, I think we need to make sure the main variant type can be properly tsubst-ed before attempting to reuse the specialization of the typedef variant type.

This sounds wrong to me: if tsubsting the TYPENAME_TYPE was going to be a problem, we ought to get that error when we instantiate the class of which the typedef is a member.

In this code example: 1 template<typename> struct A 2 { 3 typedef int X; 4 static const int i = 0; 5 }; 6 7 template<typename> struct B 8 { 9 B(const B&); // { dg-message "candidate" } 10 typedef typename A<char[A<B>::i]>::X Y; 11 template<typename T> B(T, Y); // { dg-error "call" } 12 }; 13 14 B<int> b(0,0);

There are two sets of error g++ should give us.

The first one is:
: In instantiation of 'B<int>':
:14:   instantiated from here
:10: warning: ISO C++ forbids zero-size array
: In instantiation of 'B<int>':
:14:   instantiated from here

I think it's the one you are talking about. We get that one, even if I don't add what I was refering to in the point 2/ of my previous email.

The second set of error g++ should give us is:
:11: error: no matching function for call to 'B<int>::B(int, int)'
:9: note: candidates are: B< <template-parameter-1-1> >::B(const B< <template-parameter-1-1> >&) [with <template-parameter-1-1> = int]

This second set of error is missing if I don't handle the particular case of typedef variants of TYPENAME_TYPE as was talking about in 2/.

I believe this is one is generated because during instantiation of the last parameter (namely the Y typedef) of B<int>::B(int, int), the function tsubst() receives a typedef variant of a TYPENAME_TYPE.

Before this patch, the condition:
 if (TYPE_P (t)
      && TYPE_NAME (t)
      && TYPE_NAME (t) != TYPE_MAIN_DECL (t))

was not true, because t was not a typedef variant. So t was handled by the TYPENAME_TYPE case that comes later in that function and an error was raised.

But after the patch, this condition becomes true and later this if:

&& uses_template_parms (DECL_CONTEXT (decl)))
tree tmpl = most_general_template (DECL_TI_TEMPLATE (decl));
tree gen_args = tsubst (DECL_TI_ARGS (decl), args, complain, in_decl);
r = retrieve_specialization (tmpl, gen_args, false);

becomes true as well, and later r is returned. This code path doesn't raise the error that was raised previously.

So my understanding is the typedef variant of TYPENAME_TYPE triggered a different code path that lead to some errors not being raised. I might be missing something at this point, but I can't see what :-(.

+      if (DECL_IS_BUILTIN (x)
+          || (TREE_TYPE (x) != error_mark_node
+          && TYPE_NAME (type) != x
+          /* We don't want to copy the type when all we're
+             doing is making a TYPE_DECL for the purposes of
+             inlining.  */
+          && (!TYPE_NAME (type)
+              || TYPE_NAME (type) != DECL_ABSTRACT_ORIGIN (x))))
+        clone_underlying_type (x);

This is wrong: if DECL_IS_BUILTIN (x) we don't want to create a typedef variant, we just want to set TYPE_NAME (type) to x.

Ah. I did this because clone_underlying_type handles that case of DECL_IS_BUILTING (x). I thought duplicating that here would not be desirable. So yes, the initial clone_underlying_type does more than just creating a typedef variant.



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