c++ - -Wshadow=global 将枚举类条目视为全局阴影。为什么？

Question

在 GCC 7.3 和 8.2 上使用 -Wshadow=global 进行编译时，编译器会警告以下代码片段有阴影。

constexpr int A = 0;

class Bar {
public:
    enum Bars {
        A = 0
    };
};

enum class Foo {
    A = 0     // warns this entry shadows global declaration of A
};

int main() {
    return 0;
}

<source>:11:9: warning: declaration of 'A' shadows a global declaration [-Wshadow]
     A = 0
         ^
<source>:1:15: note: shadowed declaration is here
 constexpr int A = 0;
               ^

因为枚举类在引用时需要枚举类名，我的理解是 A 的所有三个声明都是分开的:::A、::Bar::A 和 ::Foo::A。

Clang 7 不会发出带有 -Wshadow 的警告。

这是有效的阴影警告吗？如果是，为什么？

Answer 1

关于此问题的错误已提交，标题为 "-Wshadow generates an incorrect warning with enum classes" .但是，尚未确认这是一个错误。

Jonathan Wakely认为这不是错误，并给出了以下示例。

typedef unsigned char foo;
enum class myenum
{
  foo,
  bar = (foo)-1
};

Is the value -1L or 255?

If I rename myenum::foo to myenum::Foo the code silently changes meaning.

It also changes meaning if I reorder the declarations of myenum::foo and myenum::bar, which is exactly the sort of fragile code that deserves a warning.

问题中发布的示例也是如此。如果全局 int A 在 enum class Foo 之后 声明，则不再有警告。

另一个用户同意该主题:

In an ideal world we would only warn when ambiguity exists (in the user mind), that is, at "bar = (foo) -1". However, that is probably much more difficult and expensive than the current warning.