[patch] libstdc++/56158 Extend valid values of iostream bitmask types

[Martin Sebor]

On 11/11/2015 02:48 AM, Jonathan Wakely wrote:
> As described in the PR, we have operator~ overloads defined for
> enumeration types which produce values outside the range of valid
> values for the type. In C++11 that can be trivially solved by giving
> the enumeration types a fixed underlying type, but this code needs to
> be valid in C++03 too.
>
> This patch defines new min/max enumerators as INT_MIN/INT_MAX so that
> every int value is also a valid value for the bitmask type.
>
> Does anyone see any problems with this solution, or better solutions?

Just a minor nit that the C-style cast in the below triggers
a -Wold-style-cast warning in Clang, in case libstdc++ tries
to be Clang-warning free. Since the type of __INT_MAX__ is
int it shouldn't be necessary.

+      _S_ios_fmtflags_min = ~(int)__INT_MAX__

>
> Any suggestions for how to test this, given that GCC's ubsan doesn't
> check for this, and we can't run the testsuite with ubsan anyway?

Use a case/switch statement with -Werror=switch-enum to make sure
all the cases are handled and none is duplicated or outside of the
valid values of the enumeration:

   void foo (ios::iostate s) {
       switch (s) {
       case badbit:
       case eofbit:
       case failbit:
       case goodbit:
       case __INT_MAX__:
       case ~__INT_MAX__: ;
     }
   }

Martin