https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90413
Bug ID: 90413
Summary: Bad diagnostic when trying to copy an uncopyable type
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: barry.revzin at gmail dot com
Target Milestone: ---
Here's a short repro:
template<class T>
struct Bar {
Bar() {}
Bar(const Bar&) {
static_assert(sizeof(T) == 1, "");
}
};
template<class T>
struct Foo {
Foo() {}
Foo(const Foo&) = default;
Bar<T> b;
};
template<class T>
struct Baz {
Baz() {}
Baz(const Baz& o) : b(o.b) {}
Bar<T> b;
};
int main() {
#ifdef DEFAULT
Foo<int> f;
Foo<int> g = f;
#else
Baz<int> f;
Baz<int> g = f;
#endif
}
Without -DDEFAULT, the diagnostic points to the offending line (<source>:26
does appear in the trace):
<source>: In instantiation of 'Bar<T>::Bar(const Bar<T>&) [with T = int]':
<source>:17:30: required from 'Baz<T>::Baz(const Baz<T>&) [with T = int]'
<source>:26:18: required from here
<source>:5:33: error: static assertion failed
5 | static_assert(sizeof(T) == 1, "");
| ~~~~~~~~~~^~~~
Compiler returned: 1
With -DDEFAULT, the offending line disappears (no mention of <source>:23 here
at all)!
<source>: In instantiation of 'Bar<T>::Bar(const Bar<T>&) [with T = int]':
<source>:11:5: required from here
<source>:5:33: error: static assertion failed
5 | static_assert(sizeof(T) == 1, "");
| ~~~~~~~~~~^~~~
Compiler returned: 1
In larger examples, this makes it very difficult to actually find the source of
error. A larger reproduction, closer to the real example we ran into:
#include <unordered_map>
struct X {
X(X const&) = delete;
};
using Map = std::unordered_map<int, X>;
void copy_func(Map) {}
void map_error(Map& m) {
copy_func(m);
}
The 9.1 error is as follows (note that the line copy_func(m) appears nowhere in
this trace, despite being the proximal cause of offense):
In file included from
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/x86_64-linux-gnu/bits/c++allocator.h:33,
from
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/bits/allocator.h:46,
from
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/unordered_map:40,
from <source>:1:
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/ext/new_allocator.h:
In instantiation of 'void __gnu_cxx::new_allocator<_Tp>::construct(_Up*,
_Args&& ...) [with _Up = std::pair<const int, X>; _Args = {const
std::pair<const int, X>&}; _Tp = std::__detail::_Hash_node<std::pair<const int,
X>, false>]':
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/bits/alloc_traits.h:482:2:
required from 'static void std::allocator_traits<std::allocator<_Tp1>
>::construct(std::allocator_traits<std::allocator<_Tp1> >::allocator_type&,
_Up*, _Args&& ...) [with _Up = std::pair<const int, X>; _Args = {const
std::pair<const int, X>&}; _Tp = std::__detail::_Hash_node<std::pair<const int,
X>, false>; std::allocator_traits<std::allocator<_Tp1> >::allocator_type =
std::allocator<std::__detail::_Hash_node<std::pair<const int, X>, false> >]'
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/bits/hashtable_policy.h:2087:36:
required from 'std::__detail::_Hashtable_alloc<_NodeAlloc>::__node_type*
std::__detail::_Hashtable_alloc<_NodeAlloc>::_M_allocate_node(_Args&& ...)
[with _Args = {const std::pair<const int, X>&}; _NodeAlloc =
std::allocator<std::__detail::_Hash_node<std::pair<const int, X>, false> >;
std::__detail::_Hashtable_alloc<_NodeAlloc>::__node_type =
std::__detail::_Hash_node<std::pair<const int, X>, false>]'
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/bits/hashtable.h:1243:46:
required from 'std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
_H1, _H2, _Hash, _RehashPolicy, _Traits>::_Hashtable(const
std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash,
_RehashPolicy, _Traits>&) [with _Key = int; _Value = std::pair<const int, X>;
_Alloc = std::allocator<std::pair<const int, X> >; _ExtractKey =
std::__detail::_Select1st; _Equal = std::equal_to<int>; _H1 = std::hash<int>;
_H2 = std::__detail::_Mod_range_hashing; _Hash =
std::__detail::_Default_ranged_hash; _RehashPolicy =
std::__detail::_Prime_rehash_policy; _Traits =
std::__detail::_Hashtable_traits<false, false, true>]'
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/bits/unordered_map.h:181:7:
required from here
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/ext/new_allocator.h:145:20:
error: use of deleted function 'constexpr std::pair<_T1, _T2>::pair(const
std::pair<_T1, _T2>&) [with _T1 = const int; _T2 = X]'
145 | noexcept(noexcept(::new((void *)__p)
| ^~~~~~~~~~~~~~~~~~
146 | _Up(std::forward<_Args>(__args)...)))
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/unordered_map:43,
from <source>:1:
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/bits/stl_pair.h:318:17:
note: 'constexpr std::pair<_T1, _T2>::pair(const std::pair<_T1, _T2>&) [with
_T1 = const int; _T2 = X]' is implicitly deleted because the default definition
would be ill-formed:
318 | constexpr pair(const pair&) = default; ///< Copy constructor
| ^~~~
/opt/compiler-explorer/gcc-trunk-20190509/include/c++/10.0.0/bits/stl_pair.h:318:17:
error: use of deleted function 'X::X(const X&)'
<source>:4:5: note: declared here
4 | X(X const&) = delete;
| ^
Compiler returned: 1
Compile the above with clang using -stdlib=libc++ and you get, somewhere in the
trace:
<source>:12:15: note: in instantiation of member function
'std::__1::unordered_map<int, X, std::__1::hash<int>, std::__1::equal_to<int>,
std::__1::allocator<std::__1::pair<const int, X> > >::unordered_map' requested
here
copy_func(m);
^
It's still not generally a _great_ error diagnostic, but it does point me back
to the original source which makes it possible to track down the problem.
