[Bug c++/85110] Missing underlines for some bad arguments

["dmalcolm at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85110

--- Comment #3 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
Author: dmalcolm
Date: Thu Mar 29 14:43:01 2018
New Revision: 258957

URL: https://gcc.gnu.org/viewcvs?rev=258957&root=gcc&view=rev
Log:
More underlining of bad arguments (PR c++/85110)

As of r256448, the C++ frontend underlines many bad arguments in its
diagnostics; those where perform_overload_resolution returns a
non-NULL candidate, but there's a failure in convert_like_real.

However, for the case where perform_overload_resolution fails, but
there's a single non-viable candidate, the error is diagnosed by
cp_build_function_call_vec, and that currently doesn't underline
the bad argument:

$ cat test.cc
void callee (int one, const char **two, int three);

void
caller (const char *fmt)
{
  callee (1, fmt, 3);
}

We emit:

$ g++ test.cc
test.cc: In function 'void caller(const char*)':
test.cc:6:20: error: cannot convert 'const char*' to 'const char**' for
argument '2' to 'void callee(int, const char**, int)'
   callee (1, fmt, 3);
                    ^

It's going through convert_for_assignment, and
implicitly using input_location.

This patch updates convert_for_assignment for this case, using
an EXPR_LOCATION if there is one, or falling back to input_location
otherwise, underlining the argument in question:

test.cc: In function 'void caller(const char*)':
test.cc:6:14: error: cannot convert 'const char*' to 'const char**' for
argument '2' to 'void callee(int, const char**, int)'
   callee (1, fmt, 3);
              ^~~

gcc/cp/ChangeLog:
        PR c++/85110
        * typeck.c (convert_for_assignment): When complaining due to
        conversions for an argument, attempt to use the location of the
        argument.

gcc/testsuite/ChangeLog:
        PR c++/85110
        * g++.dg/diagnostic/param-type-mismatch-2.C: New test.


Added:
    trunk/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-2.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/ChangeLog