[PATCH 1/2] More underlining of bad arguments (PR c++/85110)

[David Malcolm <dmalcolm at redhat dot com>]

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);
              ^~~

Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu; adds
117 PASS results to g++.sum.

Not a regression as such, but I've been calling out the underlined
arguments as a feature of gcc 8, so would be good to fix.

OK for trunk?

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.
---
 gcc/cp/typeck.c                                    |   5 +-
 .../g++.dg/diagnostic/param-type-mismatch-2.C      | 175 +++++++++++++++++++++
 2 files changed, 178 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-2.C

diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index 0c2ebd1..e733c79 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -8781,8 +8781,9 @@ convert_for_assignment (tree type, tree rhs,
 						   parmnum, complain, flags);
 		}
 	      else if (fndecl)
-		error ("cannot convert %qH to %qI for argument %qP to %qD",
-		       rhstype, type, parmnum, fndecl);
+		error_at (EXPR_LOC_OR_LOC (rhs, input_location),
+			  "cannot convert %qH to %qI for argument %qP to %qD",
+			  rhstype, type, parmnum, fndecl);
 	      else
 		switch (errtype)
 		  {
diff --git a/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-2.C b/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-2.C
new file mode 100644
index 0000000..ae84248
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-2.C
@@ -0,0 +1,175 @@
+// { dg-options "-fdiagnostics-show-caret" }
+
+/* A collection of calls where argument 2 is of the wrong type.  */
+
+/* decl, with argname.  */
+
+extern int callee_1 (int one, const char **two, float three);
+
+int test_1 (int first, const char *second, float third)
+{
+  return callee_1 (first, second, third); // { dg-error "27: cannot convert 'const char\\*' to 'const char\\*\\*' for argument '2' to 'int callee_1\\(int, const char\\*\\*, float\\)'" }
+  /* { dg-begin-multiline-output "" }
+   return callee_1 (first, second, third);
+                           ^~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+/* decl, without argname.  */
+
+extern int callee_2 (int, const char **, float);
+
+int test_2 (int first, const char *second, float third)
+{
+  return callee_2 (first, second, third); // { dg-error "27: cannot convert 'const char\\*' to 'const char\\*\\*' for argument '2' to 'int callee_2\\(int, const char\\*\\*, float\\)'" }
+  /* { dg-begin-multiline-output "" }
+   return callee_2 (first, second, third);
+                           ^~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+/* defn, with argname.  */
+
+static int callee_3 (int one, const char **two, float three)
+{
+  return callee_2 (one, two, three);
+}
+
+int test_3 (int first, const char *second, float third)
+{
+  return callee_3 (first, second, third); // { dg-error "27: cannot convert 'const char\\*' to 'const char\\*\\*' for argument '2' to 'int callee_3\\(int, const char\\*\\*, float\\)'" }
+  /* { dg-begin-multiline-output "" }
+   return callee_3 (first, second, third);
+                           ^~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+/* static member, with argname.  */
+
+struct s4 { static int member_1 (int one, const char **two, float three); }; // { dg-line s4_member_1 }
+
+int test_4 (int first, const char *second, float third)
+{
+  return s4::member_1 (first, second, third); // { dg-error "no matching function for call to 's4::member_1\\(int&, const char\\*&, float&\\)'" }
+  /* { dg-begin-multiline-output "" }
+   return s4::member_1 (first, second, third);
+                                            ^
+     { dg-end-multiline-output "" } */
+  // { dg-message "candidate: 'static int s4::member_1\\(int, const char\\*\\*, float\\)'" "" { target *-*-* } s4_member_1 }
+  /* { dg-begin-multiline-output "" }
+ struct s4 { static int member_1 (int one, const char **two, float three); };
+                        ^~~~~~~~
+     { dg-end-multiline-output "" } */
+  // { dg-message "no known conversion for argument 2 from 'const char\\*' to 'const char\\*\\*'" "" { target *-*-* } s4_member_1 }
+  // TODO: underline the pertinent param
+}
+
+/* non-static member, with argname.  */
+
+struct s5 { int member_1 (int one, const char **two, float three); }; // { dg-line s5_member_1 }
+
+int test_5 (int first, const char *second, float third)
+{
+  s5 inst;
+  return inst.member_1 (first, second, third); // { dg-error "no matching function for call to 's5::member_1\\(int&, const char\\*&, float&\\)'" }
+  /* { dg-begin-multiline-output "" }
+   return inst.member_1 (first, second, third);
+                                             ^
+     { dg-end-multiline-output "" } */
+  // { dg-message "candidate: 'int s5::member_1\\(int, const char\\*\\*, float\\)'" "" { target *-*-* } s5_member_1 }
+  /* { dg-begin-multiline-output "" }
+ struct s5 { int member_1 (int one, const char **two, float three); };
+                 ^~~~~~~~
+     { dg-end-multiline-output "" } */
+  // { dg-message "no known conversion for argument 2 from 'const char\\*' to 'const char\\*\\*'" "" { target *-*-* } s5_member_1 }
+  // TODO: underline the pertinent param
+}
+
+/* non-static member, with argname, via a ptr.  */
+
+struct s6 { int member_1 (int one, const char **two, float three); }; // { dg-line s6_member_1 }
+
+int test_6 (int first, const char *second, float third, s6 *ptr)
+{
+  return ptr->member_1 (first, second, third); // { dg-error "no matching function for call to 's6::member_1\\(int&, const char\\*&, float&\\)'" }
+  /* { dg-begin-multiline-output "" }
+   return ptr->member_1 (first, second, third);
+                                             ^
+     { dg-end-multiline-output "" } */
+  // { dg-message "candidate: 'int s6::member_1\\(int, const char\\*\\*, float\\)'" "" { target *-*-* } s6_member_1 }
+  /* { dg-begin-multiline-output "" }
+ struct s6 { int member_1 (int one, const char **two, float three); };
+                 ^~~~~~~~
+     { dg-end-multiline-output "" } */
+  // { dg-message "no known conversion for argument 2 from 'const char\\*' to 'const char\\*\\*'" "" { target *-*-* } s6_member_1 }
+  // TODO: underline the pertinent param
+}
+
+/* Template function.  */
+
+template <typename T>
+int test_7 (int one, T two, float three); // { dg-line test_7_decl }
+
+int test_7 (int first, const char *second, float third)
+{
+  return test_7 <const char **> (first, second, third); // { dg-line test_7_usage }
+  // { dg-error "no matching function" "" { target *-*-* } test_7_usage }
+  /* { dg-begin-multiline-output "" }
+   return test_7 <const char **> (first, second, third);
+                                                      ^
+     { dg-end-multiline-output "" } */
+  // { dg-message "candidate: 'template<class T> int test_7\\(int, T, float\\)'" "" { target *-*-* } test_7_decl }
+  /* { dg-begin-multiline-output "" }
+ int test_7 (int one, T two, float three);
+     ^~~~~~
+     { dg-end-multiline-output "" } */
+  // { dg-message "template argument deduction/substitution failed:" "" { target *-*-* } test_7_decl }
+  // { dg-message "cannot convert 'second' \\(type 'const char\\*'\\) to type 'const char\\*\\*'" "" { target *-*-* } test_7_usage }
+  /* { dg-begin-multiline-output "" }
+   return test_7 <const char **> (first, second, third);
+                                         ^~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+/* Template class, static function.  */
+
+template <typename T>
+struct s8 { static int member_1 (int one, T two, float three); }; // { dg-line s8_member_1 }
+
+int test_8 (int first, const char *second, float third)
+{
+  return s8 <const char **>::member_1 (first, second, third); // { dg-error "no matching function for call to 's8<const char\\*\\*>::member_1\\(int&, const char\\*&, float&\\)'" }
+  /* { dg-begin-multiline-output "" }
+   return s8 <const char **>::member_1 (first, second, third);
+                                                            ^
+     { dg-end-multiline-output "" } */
+  // { dg-message "candidate: 'static int s8<T>::member_1\\(int, T, float\\)" "" { target *-*-* } s8_member_1 }
+  /* { dg-begin-multiline-output "" }
+ struct s8 { static int member_1 (int one, T two, float three); };
+                        ^~~~~~~~
+     { dg-end-multiline-output "" } */
+  // { dg-message "no known conversion for argument 2 from 'const char\\*' to 'const char\\*\\*'" "" { target *-*-* } s8_member_1 }
+  // TODO: underline the pertinent param
+}
+
+/* Template class, non-static function.  */
+
+template <typename T>
+struct s9 { int member_1 (int one, T two, float three); }; // { dg-line s9_member_1 }
+
+int test_9 (int first, const char *second, float third)
+{
+  s9 <const char **> inst;
+  return inst.member_1 (first, second, third); // { dg-error "no matching function for call to 's9<const char\\*\\*>::member_1\\(int&, const char\\*&, float&\\)'" }
+  /* { dg-begin-multiline-output "" }
+   return inst.member_1 (first, second, third);
+                                             ^
+     { dg-end-multiline-output "" } */
+  // { dg-message "candidate: 'int s9<T>::member_1\\(int, T, float\\)" "" { target *-*-* } s9_member_1 }
+  /* { dg-begin-multiline-output "" }
+ struct s9 { int member_1 (int one, T two, float three); };
+                 ^~~~~~~~
+     { dg-end-multiline-output "" } */
+  // { dg-message "no known conversion for argument 2 from 'const char\\*' to 'const char\\*\\*'" "" { target *-*-* } s9_member_1 }
+  // TODO: underline the pertinent param
+}
-- 
1.8.5.3