“Nested” class-template argument deduction with parentheses: GCC vs. clang

问题

Related, but (IMHO) different: Nested template argument deduction for class templates not working

The following C++17 code is rejected from GCC 8, but clang compiles it without any issues. The GCC's error message is included as a comment just before the problematic line.

Which compiler is correct here?

https://godbolt.org/z/WG6f7G

template<class T>
struct Foo {
    Foo(T) {}
};

template<class T>
struct Bar {
     Bar(T) {};
};

void works() {
    Bar bar{1};// {}
    Foo foo(bar);// ()
}

void works_too() {
    Foo foo{Bar{1}};// {{}}
}

void error_in_gcc() {
// error: 'auto' parameter not permitted in this context
    Foo foo(Bar{1});// ({})
}

void but_this_works() {
    Foo(Bar{1});// ({})
}

回答1:

Comments to this question state that this is a GCC bug. It has been filed as GCC bug report 89062.

来源：https://stackoverflow.com/questions/54369677/nested-class-template-argument-deduction-with-parentheses-gcc-vs-clang