https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95310
Bug ID: 95310
Summary: [concepts] Unrelated template parameters printed in
diagnostic
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ensadc at mailnesia dot com
CC: asutton at gcc dot gnu.org
Target Milestone: ---
https://godbolt.org/z/M8CVwc
====
template <class T>
using iter_reference_t = decltype(*T{});
template <typename F>
struct result {
using type = iter_reference_t<F>;
};
template <class Out, class T>
concept indirectly_writable = requires(Out&& o, T&& t) {
iter_reference_t<Out>(*o) = 0;
};
static_assert(indirectly_writable<const int*, int&>);
====
<source>:13:15: error: static assertion failed
13 | static_assert(indirectly_writable<const int*, int&>);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<source>:13:15: note: constraints not satisfied
<source>:10:9: required by the constraints of 'template<class Out, class T>
concept indirectly_writable'
<source>:10:31: in requirements with 'Out&& o', 'T&& t' [with F = const int*;
T = int&; Out = const int*]
<source>:11:29: note: the required expression 'decltype(*{})(*o)=0' is invalid
11 | iter_reference_t<Out>(*o) = 0;
| ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
cc1plus: note: set '-fconcepts-diagnostics-depth=' to at least 2 for more
detail
====
Note "[with F = const int*; T = int&; Out = const int*]". The 'F = const int*;'
part is spurious.
When the template parameter of `result` has the same name as the parameter of
the concept (which is the case I originally encountered), the output can be
quite confusing.
The expression 'decltype(*{})(*o)=0' also seems wrong.
Might be related to bug 94862.
