This PR points out that std::is_convertible has given the wrong answer in static_assert (!std::is_convertible_v <int () const, int (*) ()>, "");
since r13-2822 implemented __is_{,nothrow_}convertible. std::is_convertible uses the imaginary To test() { return std::declval<From>(); } to do its job. Here, From is 'int () const'. std::declval is defined as: template<class T> typename std::add_rvalue_reference<T>::type declval() noexcept; std::add_rvalue_reference is defined as "If T is a function type that has no cv- or ref- qualifier or an object type, provides a member typedef type which is T&&, otherwise type is T." In our case, T is cv-qualified, so the result is T, so we end up with int () const declval() noexcept; which is invalid. In other words, this is pretty much like: using T = int () const; T fn1(); // bad, fn returning a fn T& fn2(); // bad, cannot declare reference to qualified function type T* fn3(); // bad, cannot declare pointer to qualified function type using U = int (); U fn4(); // bad, fn returning a fn U& fn5(); // OK U* fn6(); // OK I think is_convertible_helper needs to simulate std::declval better. I wouldn't be surprised if other type traits needed a similar fix. Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/13? I've tested the new test with G++12 and clang++ as well (with std::is_convertible). PR c++/109680 gcc/cp/ChangeLog: * method.cc (is_convertible_helper): Correct simulating std::declval. gcc/testsuite/ChangeLog: * g++.dg/ext/is_convertible6.C: New test. --- gcc/cp/method.cc | 20 ++++++++++++++++++++ gcc/testsuite/g++.dg/ext/is_convertible6.C | 16 ++++++++++++++++ 2 files changed, 36 insertions(+) create mode 100644 gcc/testsuite/g++.dg/ext/is_convertible6.C diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc index 00eae56eb5b..38eb7520312 100644 --- a/gcc/cp/method.cc +++ b/gcc/cp/method.cc @@ -2245,6 +2245,26 @@ is_convertible_helper (tree from, tree to) { if (VOID_TYPE_P (from) && VOID_TYPE_P (to)) return integer_one_node; + /* std::is_{,nothrow_}convertible test whether the imaginary function + definition + + To test() { return std::declval<From>(); } + + is well-formed. A function can't return a function... */ + if (FUNC_OR_METHOD_TYPE_P (to) + /* ...neither can From be a function with cv-/ref-qualifiers: + std::declval is defined as + + template<class T> + typename std::add_rvalue_reference<T>::type declval() noexcept; + + and std::add_rvalue_reference yields T when T is a function with + cv- or ref-qualifiers, making the definition ill-formed. + ??? Should we check this in other uses of build_stub_object too? */ + || (FUNC_OR_METHOD_TYPE_P (from) + && (type_memfn_quals (from) != TYPE_UNQUALIFIED + || type_memfn_rqual (from) != REF_QUAL_NONE))) + return error_mark_node; cp_unevaluated u; tree expr = build_stub_object (from); deferring_access_check_sentinel acs (dk_no_deferred); diff --git a/gcc/testsuite/g++.dg/ext/is_convertible6.C b/gcc/testsuite/g++.dg/ext/is_convertible6.C new file mode 100644 index 00000000000..180582663e8 --- /dev/null +++ b/gcc/testsuite/g++.dg/ext/is_convertible6.C @@ -0,0 +1,16 @@ +// PR c++/109680 +// { dg-do compile { target c++11 } } + +#define SA(X) static_assert((X),#X) + +SA(!__is_convertible(int () const, int (*)())); +SA(!__is_convertible(int (*)(), int () const)); + +SA( __is_convertible(int (), int (*)())); +SA(!__is_convertible(int (*)(), int ())); + +SA( __is_convertible(int (int), int (*) (int))); +SA(!__is_convertible(int (*) (int), int (int))); + +SA(!__is_convertible(int (int) const, int (*) (int))); +SA(!__is_convertible(int (*) (int), int (int) const)); base-commit: 33020780a9699f1146eeed61783cec89fde337a0 -- 2.40.1