Created attachment 51127 [details] a diagnositic message to print functions arguments for comparison This example code from core 1001(http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1001) is still giving no matching template declaration error. template<class T> struct A { typedef T arr[3]; }; template<class T> void f(const typename A<T>::arr) { } // #1 template void f<int>(const A<int>::arr); 1. This happens for all gcc versions. The root cause is template function argument is considered as ‘(const int*)’ instead of ‘(int*)’ (see attached debug output for details.) 2. C++ standard requires top level cv qualifier being dropped when forming function type.(https://timsong-cpp.github.io/cppwp/dcl.fct#5) 3. When both 'const' are removed from template function and specialization, there is no error which proves array type works as long as there is no top level cv qualifier. 4. I feel this is rather a high-profile bug as the example code is listed in active core language issues long ago, particularly when both clang and MSVC have fixed this issue. (see godbolt: https://www.godbolt.org/z/cofrEWEbs)
(In reply to nick huang from comment #0) > This example code from core > 1001(http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1001) is > still giving no matching template declaration error. The issue is still open and has not been resolved yet. > 2. C++ standard requires top level cv qualifier being dropped when forming > function type.(https://timsong-cpp.github.io/cppwp/dcl.fct#5) Yes, that's what the issue quotes, and it also says "It is not clear how or whether this adjustment should be applied to parameters of function templates when the parameter has a dependent type, however." > > 3. When both 'const' are removed from template function and specialization, > there is no error which proves array type works as long as there is no top > level cv qualifier. > > 4. I feel this is rather a high-profile bug as the example code is listed in > active core language issues long ago, The issue is still active, meaning the standard has not been fixed to say what the correct behaviour is.
We already have a bug for this. *** This bug has been marked as a duplicate of bug 51851 ***
bug 51851 has been fixed by latest release/gcc-10, but not this issue. So, I suggest to change this bug status to New.
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>: https://gcc.gnu.org/g:79802c5dcc043a515f429bb2bec7573b8537c32a commit r12-4453-g79802c5dcc043a515f429bb2bec7573b8537c32a Author: Jason Merrill <jason@redhat.com> Date: Tue Sep 28 10:02:04 2021 -0400 c++: array cv-quals and template specialization [PR101402] PRs 101402, 102033, etc. demonstrated that the fix for PR92010 wasn't handling all cases of the CWG1001/1322 issue with parameter type qual stripping and arrays with templates. The problem turned out to be in determine_specialization, which did an extra substitution without the 92010 fix and then complained that the result didn't match. But just removing that wrong/redundant code meant that we were accepting specializations with different numbers of parameters, because the code in fn_type_unification that compares types in this case wasn't checking for length mismatch. After fixing that, I realized that fn_type_unification couldn't tell the difference between variadic and non-variadic function types, because the args array doesn't include the terminal void we use to indicate non-variadic function type. So I added it, and made the necessary adjustments. Thanks to qingzhe "nick" huang <nickhuang99@hotmail.com> for the patch that led me to dig more into this, and the extensive testcases. PR c++/51851 PR c++/101402 PR c++/102033 PR c++/102034 PR c++/102039 PR c++/102044 gcc/cp/ChangeLog: * pt.c (determine_specialization): Remove redundant code. (fn_type_unification): Check for mismatched length. (type_unification_real): Ignore terminal void. (get_bindings): Don't stop at void_list_node. * class.c (resolve_address_of_overloaded_function): Likewise. gcc/testsuite/ChangeLog: * g++.dg/template/fnspec2.C: New test. * g++.dg/template/parm-cv1.C: New test. * g++.dg/template/parm-cv2.C: New test. * g++.dg/template/parm-cv3.C: New test.