[Bug c++/99518] New: trailing requires clause adds nonexistent reference declarator to function parameter

[Bug c++/99518] New: trailing requires clause adds nonexistent reference declarator to function parameter

[nickgray0 at brown dot edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99518

            Bug ID: 99518
           Summary: trailing requires clause adds nonexistent reference
                    declarator to function parameter
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nickgray0 at brown dot edu
  Target Milestone: ---

the following code fails to compile

    #include <concepts>

    auto f(std::integral auto x) {}
    auto g(auto x) requires requires { { x }->std::integral; } {}

    auto main()->int {
        f(42); // OK
        g(42); // error
    }



error message: In function 'int main()':
<source>:8:9: error: no matching function for call to 'g(int)'
    8 |     g(42); // error
      |         ^
<source>:4:6: note: candidate: 'template<class auto:2> auto g(auto:2) requires
requires{{g::x} -> decltype(auto) [requires std::integral<<placeholder>, >];}'
    4 | auto g(auto x) requires requires { { x }->std::integral; } {}
      |      ^
<source>:4:6: note:   template argument deduction/substitution failed:
<source>:4:6: note: constraints not satisfied
<source>: In substitution of 'template<class auto:2> auto g(auto:2) requires
requires{{x} -> decltype(auto) [requires std::integral<<placeholder>, >];}
[with auto:2 = int]':
<source>:8:9:   required from here
<source>:4:6:   required by the constraints of 'template<class auto:2> auto
g(auto:2) requires requires{{x} -> decltype(auto) [requires
std::integral<<placeholder>, >];}'
<source>:4:25:   in requirements  [with auto:2 = int]
<source>:4:38: note: 'x' does not satisfy return-type-requirement, because
    4 | auto g(auto x) requires requires { { x }->std::integral; } {}
      |                                      ^
<source>:4:38: error: deduced expression type does not satisfy placeholder
constraints
    4 | auto g(auto x) requires requires { { x }->std::integral; } {}
      |                                    ~~^~~~~~~~~~~~~~~~~~
<source>:4:38: note: constraints not satisfied
In file included from <source>:1:
/opt/compiler-explorer/gcc-trunk-20210310/include/c++/11.0.1/concepts:102:13:  
required for the satisfaction of 'integral<decltype(auto) [requires
std::integral<<placeholder>, >]>' [with decltype(auto) [requires
std::integral<<placeholder>, >] = int&]
/opt/compiler-explorer/gcc-trunk-20210310/include/c++/11.0.1/concepts:102:24:
note: the expression 'is_integral_v<_Tp> [with _Tp = int&]' evaluated to
'false'
  102 |     concept integral = is_integral_v<_Tp>;

[Bug c++/99518] trailing requires clause adds nonexistent reference declarator to function parameter

[nickgray0 at brown dot edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99518

--- Comment #1 from nickgray0 at brown dot edu ---
I just looked up the standard and it seems GCC is correct to reject the code
and Clang's implementation (which happily compiles the code) is incorrect. the
compound requirement requires the parenthesized expression (which in this case,
turns 'x' to int&) to satisfy the return type constraint.

Sorry for the false alarm.

[Bug c++/99518] trailing requires clause adds nonexistent reference declarator to function parameter

[nickgray0 at brown dot edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99518

nickgray0 at brown dot edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from nickgray0 at brown dot edu ---
closed