Consider this bogus code (from g++.dg/diagnostic/param-type-mismatch-2.C):

struct s4 { static int member_1 (int one, const char **two, float three); };

int test_4 (int first, const char *second, float third)
{
  return s4::member_1 (first, second, third);
}

Before this patch, g++ emits:

demo.cc: In function 'int test_4(int, const char*, float)':
demo.cc:5:44: error: no matching function for call to 's4::member_1(int&, const char*&, float&)'
5 |   return s4::member_1 (first, second, third);
  |                                            ^
demo.cc:1:24: note: candidate: 'static int s4::member_1(int, const char**, float)'
1 | struct s4 { static int member_1 (int one, const char **two, float three); };
  |                        ^~~~~~~~
demo.cc:1:24: note:   no known conversion for argument 2 from 'const char*' to 'const char**'

With this patch, it highlights the pertinent parameter in the
"no known conversion" note:

demo.cc: In function 'int test_4(int, const char*, float)':
demo.cc:5:44: error: no matching function for call to 's4::member_1(int&, const char*&, float&)'
5 |   return s4::member_1 (first, second, third);
  |                                            ^
demo.cc:1:24: note: candidate: 'static int s4::member_1(int, const char**, float)'
1 | struct s4 { static int member_1 (int one, const char **two, float three); };
  |                        ^~~~~~~~
demo.cc:1:56: note:   no known conversion for argument 2 from 'const char*' to 'const char**'
1 | struct s4 { static int member_1 (int one, const char **two, float three); };
  |                                           ~~~~~~~~~~~~~^~~

gcc/cp/ChangeLog:
	PR c++/85110
	* call.c (print_conversion_rejection): Add "fn" param and use it
	for "no known conversion" messages to underline the pertinent
	param.
	(print_z_candidate): Supply "fn" to the new param above.

gcc/testsuite/ChangeLog:
	PR c++/85110
	* g++.dg/diagnostic/param-type-mismatch-2.C: Update expected
	output to reflect underlining of pertinent parameter in decl
	for "no known conversion" messages.

From-SVN: r263957