[Bug c++/89997] Garbled expression in error message with -fconcepts

["pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89997

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
In GCC 10+ (with -fconcepts-diagnostics-depth=2), GCC produces:


<source>: In function 'void test()':
<source>:17:16: error: use of function 'void check() requires requires(X x, T
val) {x.X::operator<<()("hello") << val;} [with T = int]' with unsatisfied
constraints
   17 |     check<int>(); // mangled error
      |                ^
<source>:13:6: note: declared here
   13 | void check() requires requires (X x, T val) { x << "hello" << val; } {}
      |      ^~~~~
<source>:13:6: note: constraints not satisfied
<source>: In instantiation of 'void check() requires requires(X x, T val)
{x.X::operator<<()("hello") << val;} [with T = int]':
<source>:17:16:   required from here
<source>:13:6:   required by the constraints of 'template<class T> void check()
requires requires(X x, T val) {x.X::operator<<()("hello") << val;}'
<source>:13:23:   in requirements with 'X x', 'T val' [with T = int]
<source>:13:60: note: the required expression '("hello"->x.X::operator<<() <<
val)' is invalid, because
   13 | void check() requires requires (X x, T val) { x << "hello" << val; } {}
      |                                               ~~~~~~~~~~~~~^~~~~~
<source>:13:63: error: invalid conversion from 'int' to 'void*' [-fpermissive]
   13 | void check() requires requires (X x, T val) { x << "hello" << val; } {}
      |                                                               ^~~
      |                                                               |
      |                                                               int
<source>:9:19: note:   initializing argument 1 of 'X Y::operator<<(void*)'
    9 |     X operator<< (void*);
      |                   ^~~~~

Is this good enoug now?


Note clang produces:
<source>:17:5: error: no matching function for call to 'check'
    check<int>(); // mangled error
    ^~~~~~~~~~
<source>:13:6: note: candidate template ignored: constraints not satisfied
[with T = int]
void check() requires requires (X x, T val) { x << "hello" << val; } {}
     ^
<source>:13:60: note: because 'x << "hello" << val' would be invalid: invalid
operands to binary expression ('Y' and 'int')
void check() requires requires (X x, T val) { x << "hello" << val; } {}
                                                           ^