https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89997
Bug ID: 89997
Summary: Garbled expression in error message with -fconcepts
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redbeard0531 at gmail dot com
Target Milestone: ---
Usually -fconcepts delivers excellent error messages, but this one is pretty
bad. It looks like this goes back to 6.2, when it first started to show the
expression.
https://godbolt.org/z/m9DlOZ
struct Y;
struct X {
Y operator<< (const char*);
};
struct Y {
X operator<< (void*);
};
template <typename T>
void check() requires requires (X x, T val) { x << "hello" << val; } {}
void test() {
check<int*>(); // no error
check<int>(); // mangled error
}
-------------
<source>: In function 'void test()':
<source>:16:16: error: cannot call function 'void check() requires (<requires
(X x, T val) <valid-expression (x.X::operator<<()("hello") << val)>> [with T =
int]'
16 | check<int>(); // mangled error
| ^
<source>:12:6: note: constraints not satisfied
12 | void check() requires requires (X x, T val) { x << "hello" << val; } {}
| ^~~~~
<source>:12:6: note: with 'X x'
<source>:12:6: note: with 'int val'
<source>:12:6: note: the required expression '("hello"->x.X::operator<<() <<
val)' would be ill-formed
What is that expression? How did it end up applying -> to a string literal!?
