Proposed resolution (2025-01-21, approved by CWG 2025-02-14):

Change in 9.12.10 [dcl.attr.nodiscard] paragraph 4 as follows:

Recommended practice: Appearance of a nodiscard call as a potentially-evaluated discarded-value expression (7.2 [expr.prop]) of non-void type is discouraged unless explicitly cast to void. Implementations should issue a warning in such cases. The value of a has-attribute-expression for the nodiscard attribute should be 0 unless the implementation can issue such warnings.

(From submission #628.)

A warning is currently, but ought not to be, encouraged for a call to a [[nodiscard]] function with a void return type. Such a situation may arise for dependent return types. For example:

  [[nodiscard]] void f();
  template<class T> [[nodiscard]] T g();

  void h() {
    f();                // suggested change: warning no longer recommended
    (void)f();          // warning not recommended
    g<int>();           // warning recommended
    g<void>();          // suggested change: warning no longer recommended
    (void)g<void>();    // warning not recommended
  }