llvm-project/clang/test/SemaCXX/implicit-exception-spec.cpp

// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -verify -std=c++11 -Wall %s

template<bool b> struct ExceptionIf { static int f(); };
template<> struct ExceptionIf<false> { typedef int f; };

// The exception specification of a defaulted default constructor depends on
// the contents of in-class member initializers. However, the in-class member
// initializers can depend on the exception specification of the constructor,
// since the class is considered complete within them. We reject any such cases.
namespace InClassInitializers {
  // Noexcept::Noexcept() is implicitly declared as noexcept(false), because it
  // directly invokes ThrowSomething(). However...
  //
  // If noexcept(Noexcept()) is false, then Noexcept() is a constant expression,
  // so noexcept(Noexcept()) is true. But if noexcept(Noexcept()) is true, then
  // Noexcept::Noexcept is not declared constexpr, therefore noexcept(Noexcept())
  // is false.
  bool ThrowSomething() noexcept(false);
  struct ConstExpr {
    bool b = noexcept(ConstExpr()) && ThrowSomething(); // expected-error {{exception specification is not available until end of class definition}}
  };
  // We can use it now.
  bool w = noexcept(ConstExpr());

  // Much more obviously broken: we can't parse the initializer without already
  // knowing whether it produces a noexcept expression.
  struct TemplateArg {
    int n = ExceptionIf<noexcept(TemplateArg())>::f(); // expected-error {{exception specification is not available until end of class definition}}
  };
  bool x = noexcept(TemplateArg());

  // And within a nested class.
  struct Nested {
    struct Inner {
      int n = ExceptionIf<noexcept(Nested())>::f(); // expected-error {{exception specification is not available until end of class definition}}
    } inner;
  };
  bool y = noexcept(Nested());
  bool z = noexcept(Nested::Inner());
}

// FIXME:
// The same problem arises in delayed parsing of exception specifications,
// which clang does not yet support.
namespace ExceptionSpecification {
  struct Nested { // expected-note {{not complete}}
    struct T {
      T() noexcept(!noexcept(Nested())); // expected-error {{incomplete type}}
    } t;
  };
}

// FIXME:
// The same problem arises in delayed parsing of default arguments,
// which clang does not yet support.
namespace DefaultArgument {
  struct Default { // expected-note {{defined here}}
    struct T {
      T(int = ExceptionIf<noexcept(Default())::f()); // expected-error {{call to implicitly-deleted default constructor}}
    } t;
  };
}