[C++ Patch / RFC] PR 51242

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,

this PR is about the rejection (in C++11 mode of course) of:

enum class MyEnum { A = 1 };

struct MyClass
{
  MyEnum Field1 : 3;
};


whereas the corresponding unscoped enum case already works. As noticed 
by Jon, it seems that the below straightforward patchlet is enough to 
solve the problem but then we have a warning issue:

51242.C:5:19: warning: ‘MyClass::Field1’ is too small to hold all values 
of ‘enum class MyEnum’ [enabled by default]

which is easily explained: the underlying type is fixed (to an implicit 
int type), thus in finish_enum_value_list, fixed_underlying_type_p is 
true and the code "restricting" the ENUM_UNDERLYING_TYPE for diagnostic 
purposes doesn't run. In other terms, we warn for the same reason we for 
example -Wnarrowing warn (before erroring out) for:

enum class Code {
  SUCCESS = 0
};

Code a;

short r[] = {a};


That seems intended, but especially annoying in the bitfield case. An 
idea could be giving a name to the "too small to hold all values" 
warning and making possible disabling it. What do you suggest?

Thanks!
Paolo.

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