相关疑难解决方法(0)

与 GCC 12.2 和 MSVC 19.33 相比，以下代码示例不能使用 Clang 15 或 Clang trunk 进行编译。嵌套required子句中的约束表达式是否无效？

struct t {
    constexpr auto b() const noexcept
    { return true; }
};

template<typename T>
concept c = requires(T t) {
    requires t.b();
};

static_assert(c<t>);

Clang 产生的错误消息：

<source>:11:1: error: static assertion failed
static_assert(c<t>);
^             ~~~~
<source>:11:15: note: because 't' does not satisfy 'c'
static_assert(c<t>);
              ^
<source>:8:14: note: because 't.b()' would be invalid: constraint variable 't'
cannot be used in an evaluated context
    requires t.b();
             ^ …