Bug 102039 - another case of template function signature incorrectly dropping top-level cv-qualifier with function parameter dependent on template argument
Summary: another case of template function signature incorrectly dropping top-level cv...
Status: RESOLVED FIXED
Alias: None
Product: gcc
Classification: Unclassified
Component: c++ (show other bugs)
Version: 10.2.0
: P3 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL:
Keywords: rejects-valid
Depends on:
Blocks: 24666
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Reported: 2021-08-24 12:17 UTC by qingzhe huang
Modified: 2021-10-25 08:59 UTC (History)
1 user (show)

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Description qingzhe huang 2021-08-24 12:17:56 UTC
You can say this is another dup of PR101402, but the nature is different because the dependent-type is now from function template argument itself which is different from another template class of PR101402. And that is why I file it to be a possibly future test case.

struct A{
        typedef int Arr3[3];
};

template<class T>
void f(const typename T::Arr3){}

template<>
void f<A>(const int[3]){}
Comment 1 Andrew Pinski 2021-08-24 22:32:13 UTC
This is another one where the arrays decay too fast to pointers in the argument.

Or rather not fast enough:
struct A{
        typedef int Arr3[3];
};
template<class T>
void f(const typename T::Arr3){}
template<>
void f<A>(const int*){}

Or maybe not, I will leave this more to C++ standards expert because ICC (EDG) also rejects both of these testcases for the same reason as GCC.
Comment 2 GCC Commits 2021-10-15 21:00:42 UTC
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.
Comment 3 qingzhe huang 2021-10-25 08:59:58 UTC
fixed by patch under PR101402