[Bug c++/82334] improve list of candidates for a member definition that doesn't match declaration

[Bug c++/82334] improve list of candidates for a member definition that doesn't match declaration

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82334

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2017-09-27 00:00:00         |2021-8-9

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This example is from PR 101811

struct X {
    void f();
};

template<int i>  // this line should not be here
void X::f()
{}

GCC is pretty bad here:

<source>:6:6: error: no declaration matches 'void X::f()'
    6 | void X::f()
      |      ^
<source>:2:10: note: candidate is: 'void X::f()'
    2 |     void f();
      |          ^
<source>:1:8: note: 'struct X' defined here
    1 | struct X {
      |        ^

But Clang is no better:

<source>:6:9: error: out-of-line definition of 'f' does not match any
declaration in 'X'
void X::f()
        ^
<source>:2:10: note: member declaration nearly matches
    void f();
         ^

It seems to give up on noticing why the candidate doesn't match and just says
"nearly matches" as a generic fallback.

To fix this bug will need a list of things to check for. Did it fail to match
because one is cv-qualified and the other isn't? Maybe one is ref-qualified and
the other isn't? Maybe one is a function template and the other isn't? Maybe
the number or type of parameter (or template parameters) doesn't match etc.