[Bug c++/125406] New: No warning for using a [[deprecated]] enum in a variable template

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125406

            Bug ID: 125406
           Summary: No warning for using a [[deprecated]] enum in a
                    variable template
           Product: gcc
           Version: 16.1.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

template<typename T>
struct limits
{
  [[deprecated]] static constexpr int value = 1;
};

#ifdef WARNS
static_assert( limits<int>::value == 1 );
#else
template<typename T> constexpr bool var = limits<T>::value == 1;
static_assert( var<int> );
#endif

With -DWARNS defined we get a warning as expected:

e.cc:8:29: warning: ‘limits<int>::value’ is deprecated
[-Wdeprecated-declarations]
    8 | static_assert( limits<int>::value == 1 );
      |                             ^~~~~
e.cc:4:39: note: declared here
    4 |   [[deprecated]] static constexpr int value = 1;
      |                                       ^~~~~

But without -DWARNS (when the deprecated member is used in the variable
template's initializer) there is no warning.