https://gcc.gnu.org/bugzilla/show_bug.cgi?id=44283
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |error-recovery
Status|UNCONFIRMED |NEW
Last reconfirmed| |2017-08-18
CC| |egallager at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #2 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #0)
> namespace NS
> {
> typedef int X;
>
> template<typename T> void f(X f, T t) { }
> }
>
> template void f(X, int); // (1)
>
> template void f(int, char); // (2)
>
>
> The code is invalid, the explicit instantiations should be inside NS or
> should be qualified e.g.
> template void NS::func(X, int);
>
> But the diagnostic for instantiation (1) is unhelpful:
>
> bug.cc:8:17: error: variable or field 'f' declared void
> bug.cc:8:16: error: expected ';' before '(' token
>
> This is closely related to Bug 16663 but the diagnostic for (2) implies it
> might be possible to improve things without fixing bug 16663, as this is
> much better:
>
> bug.cc:10:26: error: 'f' is not a template function
>
> Is it possible to give the same "is not a template function" diagnostic for
> (1)?
The message is now:
$ /usr/local/bin/g++ -c -Wall -Wextra -pedantic 44283.cc
44283.cc:8:17: error: variable or field ‘f’ declared void
template void f(X, int); // (1)
^
44283.cc:8:16: error: expected ‘;’ before ‘(’ token
template void f(X, int); // (1)
^
44283.cc:10:26: error: ‘f’ is not a template function
template void f(int, char); // (2)
^
$
so it has the "is not a template function" diagnostic now, but it could still
probably be improved.
>
> Comeau does significantly better, reporting:
> identifier "X" is undefined
> and
> "f" is not a class or function template name in the current scope
>
>
>
> If the invalid instantiation is for a class template the diagnostic is fine:
>
> namespace NS
> {
> template<typename T> struct S;
> }
>
> template struct S<X>;
>
> bug2.cc:6:17: error: 'S' is not a template
> bug2.cc:6:19: error: 'X' was not declared in this scope
> bug2.cc:6:17: error: explicit instantiation of non-template type 'S'
>
> The only improvement I would make would be to add something like "in this
> scope" to the first error.
>
With carets, this is now:
$ /usr/local/bin/g++ -c -Wall -Wextra -pedantic 44283_2.cc
44283_2.cc:6:17: error: ‘S’ is not a class template
template struct S<X>;
^
44283_2.cc:6:19: error: ‘X’ was not declared in this scope
template struct S<X>;
^
44283_2.cc:6:17: error: explicit instantiation of non-template type ‘S’
template struct S<X>;
^
$
(note the addition of the word 'class')
>
> Here's another bad diagnostic for instantiating a template function, which
> doesn't have any undeclared type:
>
> namespace NS
> {
> template<int N> void g() { }
> }
>
> template void g<0>();
>
> bug3.cc:6:15: error: variable or field 'g' declared void
> bug3.cc:6:16: error: expected ';' before '<' token
>
> Surely it's possible to say "g is not a template function" when the compiler
> sees "template ... g<...>" ?
>
This is still bad even with carets:
$ /usr/local/bin/g++ -c -Wall -Wextra -pedantic 44283_3.cc
44283_3.cc:6:15: error: variable or field ‘g’ declared void
template void g<0>();
^
44283_3.cc:6:16: error: expected ‘;’ before ‘<’ token
template void g<0>();
^
$
> Comeau is much better again:
>
> "ComeauTest.c", line 6: error: g is not a template,
> Should it be XX::g?, where XX is some namespace?
> Did you #include the right header?
> template void g<0>();
> ^
>
> "ComeauTest.c", line 6: error: invalid explicit instantiation declaration
> template void g<0>();
> ^
So, confirmed that the errors could be improved.
