http://gcc.gnu.org/bugzilla/show_bug.cgi?id=99
--- Comment #20 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Wolfgang Bangerth from comment #11)
> Here's another very nice example from PR 20313:
> -------------------------
> template<int j> struct s;
> template<int i> s<i>::s(int j) {}
> -------------------------
> Note that the definition of the constructor is invalid because the struct
> isn't complete. Here's what we get:
> g/x> /home/bangerth/bin/gcc-4.0-pre/bin/c++ -c x.cc
> x.cc:2: error: invalid use of undefined type ?struct s<j>?
> x.cc:1: error: declaration of ?struct s<j>?
> x.cc:2: error: template definition of non-template ?s<j>::s(int)?
>
> Note how the compiler uses the template argument 'j', although we use
> template argument 'i' in line 2!
I have been doing a bit more analysis and it is not very clear what would be
the correct output in this example. For the slightly different testcase:
template<int x> struct s;
template<int i> s<i>::s(int j) {}
GCC 4.9 prints:
/home/manuel/test1/pr99.cc:2:30: error: invalid use of incomplete type ‘struct
s<x>’
template<int i> s<i>::s(int j) {}
^
/home/manuel/test1/pr99.cc:1:24: error: declaration of ‘struct s<x>’
template<int x> struct s;
^
If we do this change:
Index: pt.c
===================================================================
--- pt.c (revision 209347)
+++ pt.c (working copy)
@@ -7574,10 +7574,11 @@ lookup_template_class_1 (tree d1, tree a
class, however, such a reference is an instantiation. */
if ((entering_scope
|| !PRIMARY_TEMPLATE_P (gen_tmpl)
|| currently_open_class (template_type))
/* comp_template_args is expensive, check it last. */
+ && false
&& comp_template_args (TYPE_TI_ARGS (template_type),
arglist))
return template_type;
/* If we already have this specialization, return it. */
then it prints:
/home/manuel/test1/pr99.cc:2:30: error: invalid use of incomplete type ‘struct
s<i>’
template<int i> s<i>::s(int j) {}
^
/home/manuel/test1/pr99.cc:1:24: error: declaration of ‘struct s<i>’
template<int x> struct s;
^
I am not sure one output is better than the other.
