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[PATCH v2] C++: improvements to diagnostics using %P (more PR c++/85110)


I was going to ping this patch:
  https://gcc.gnu.org/ml/gcc-patches/2018-11/msg00875.html
but it has bit-rotted somewhat, so here's a refreshed version of it.

Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.

OK for trunk?

Thanks
Dave


Blurb from v1:

This patch is based on grepping the C++ frontend for %P
i.e. diagnostics that refer to a parameter number.  It fixes up
these diagnostics to highlight the pertinent param where appropriate
(and possible), along with various other tweaks, as described in the
ChangeLog.

gcc/cp/ChangeLog:
	PR c++/85110
	* call.c (conversion_null_warnings): Try to use the location of
	the expression for the warnings.  Add notes showing the parameter
	of the function decl, where available.
	(get_fndecl_argument_location): Gracefully reject
	non-FUNCTION_DECLs.  For implicitly-declared functions, use the
	fndecl location rather than that of the param.
	(maybe_inform_about_fndecl_for_bogus_argument_init): New function.
	(convert_like_real): Use it in various places to avoid repetition.
	* cp-tree.h (maybe_inform_about_fndecl_for_bogus_argument_init):
	New declaration.
	* decl2.c: Include "gcc-rich-location.h".
	(check_default_args): Use the location of the parameter when
	complaining about parameters with missing default arguments in
	preference to that of the fndecl.
	Attempt to record the location of first parameter with a default
	argument and add it as a secondary range to such errors.
	* typeck.c (convert_arguments): When complaining about parameters
	with incomplete types, attempt to use the location of the
	argument.  Where available, add a note showing the pertinent
	parameter in the fndecl.
	(convert_for_assignment): When complaining about bad conversions
	at function calls, use the location of the unstripped argument.
	(convert_for_initialization): When checking for bogus references,
	add an auto_diagnostic_group, and update the note to use the
	location of the pertinent parameter, rather than just the callee.

gcc/testsuite/ChangeLog:
	PR c++/85110
	* g++.dg/diagnostic/missing-default-args.C: New test.
	* g++.dg/diagnostic/param-type-mismatch-3.C: New test.
	* g++.dg/diagnostic/param-type-mismatch.C: Add tests for invalid
	references and incomplete types.
	* g++.dg/warn/Wconversion-null-4.C: New test.
---
 gcc/cp/call.c                                      | 88 ++++++++++++++--------
 gcc/cp/cp-tree.h                                   |  1 +
 gcc/cp/decl2.c                                     | 16 +++-
 gcc/cp/typeck.c                                    | 22 ++++--
 .../g++.dg/diagnostic/missing-default-args.C       | 53 +++++++++++++
 .../g++.dg/diagnostic/param-type-mismatch-3.C      | 26 +++++++
 .../g++.dg/diagnostic/param-type-mismatch.C        | 41 ++++++++++
 gcc/testsuite/g++.dg/warn/Wconversion-null-4.C     | 43 +++++++++++
 8 files changed, 251 insertions(+), 39 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/diagnostic/missing-default-args.C
 create mode 100644 gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-3.C
 create mode 100644 gcc/testsuite/g++.dg/warn/Wconversion-null-4.C

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index ee099cc..cfc5641 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -6681,16 +6681,24 @@ conversion_null_warnings (tree totype, tree expr, tree fn, int argnum)
   if (null_node_p (expr) && TREE_CODE (totype) != BOOLEAN_TYPE
       && ARITHMETIC_TYPE_P (totype))
     {
-      location_t loc =
-	expansion_point_location_if_in_system_header (input_location);
-
       if (fn)
-	warning_at (loc, OPT_Wconversion_null,
-		    "passing NULL to non-pointer argument %P of %qD",
-		    argnum, fn);
+	{
+	  location_t loc = EXPR_LOC_OR_LOC (expr, input_location);
+	  loc = expansion_point_location_if_in_system_header (loc);
+	  auto_diagnostic_group d;
+	  if (warning_at (loc, OPT_Wconversion_null,
+			  "passing NULL to non-pointer argument %P of %qD",
+			  argnum, fn))
+	    inform (get_fndecl_argument_location (fn, argnum),
+		    "  declared here");
+	}
       else
-	warning_at (loc, OPT_Wconversion_null,
-		    "converting to non-pointer type %qT from NULL", totype);
+	{
+	  location_t loc
+	    = expansion_point_location_if_in_system_header (input_location);
+	  warning_at (loc, OPT_Wconversion_null,
+		      "converting to non-pointer type %qT from NULL", totype);
+	}
     }
 
   /* Issue warnings if "false" is converted to a NULL pointer */
@@ -6698,9 +6706,15 @@ conversion_null_warnings (tree totype, tree expr, tree fn, int argnum)
 	   && TYPE_PTR_P (totype))
     {
       if (fn)
-	warning_at (input_location, OPT_Wconversion_null,
-		    "converting %<false%> to pointer type for argument %P "
-		    "of %qD", argnum, fn);
+	{
+	  location_t loc = EXPR_LOC_OR_LOC (expr, input_location);
+	  auto_diagnostic_group d;
+	  if (warning_at (loc, OPT_Wconversion_null,
+			  "converting %<false%> to pointer type for argument "
+			  "%P of %qD", argnum, fn))
+	    inform (get_fndecl_argument_location (fn, argnum),
+		    "  declared here");
+	}
       else
 	warning_at (input_location, OPT_Wconversion_null,
 		    "converting %<false%> to pointer type %qT", totype);
@@ -6740,6 +6754,15 @@ maybe_print_user_conv_context (conversion *convs)
 location_t
 get_fndecl_argument_location (tree fndecl, int argnum)
 {
+  /* Gracefully fail for e.g. TEMPLATE_DECL.  */
+  if (TREE_CODE (fndecl) != FUNCTION_DECL)
+    return DECL_SOURCE_LOCATION (fndecl);
+
+  /* The locations of implicitly-declared functions are likely to be
+     more meaningful than those of their parameters.  */
+  if (DECL_ARTIFICIAL (fndecl))
+    return DECL_SOURCE_LOCATION (fndecl);
+
   int i;
   tree param;
 
@@ -6757,6 +6780,18 @@ get_fndecl_argument_location (tree fndecl, int argnum)
   return DECL_SOURCE_LOCATION (param);
 }
 
+/* If FNDECL is non-NULL, issue a note highlighting ARGNUM
+   within its declaration (or the fndecl itself if something went
+   wrong).  */
+
+void
+maybe_inform_about_fndecl_for_bogus_argument_init (tree fn, int argnum)
+{
+  if (fn)
+    inform (get_fndecl_argument_location (fn, argnum),
+	    "  initializing argument %P of %qD", argnum, fn);
+}
+
 /* Perform the conversions in CONVS on the expression EXPR.  FN and
    ARGNUM are used for diagnostics.  ARGNUM is zero based, -1
    indicates the `this' argument of a method.  INNER is nonzero when
@@ -6834,9 +6869,8 @@ convert_like_real (conversion *convs, tree expr, tree fn, int argnum,
 					     complain);
 	      else
 		expr = cp_convert (totype, expr, complain);
-	      if (complained && fn)
-		inform (DECL_SOURCE_LOCATION (fn),
-			"  initializing argument %P of %qD", argnum, fn);
+	      if (complained)
+		maybe_inform_about_fndecl_for_bogus_argument_init (fn, argnum);
 	      return expr;
 	    }
 	  else if (t->kind == ck_user || !t->bad_p)
@@ -6863,9 +6897,8 @@ convert_like_real (conversion *convs, tree expr, tree fn, int argnum,
 				  "invalid conversion from %qH to %qI",
 				  TREE_TYPE (expr), totype);
 	}
-      if (complained && fn)
-	inform (get_fndecl_argument_location (fn, argnum),
-		"  initializing argument %P of %qD", argnum, fn);
+      if (complained)
+	maybe_inform_about_fndecl_for_bogus_argument_init (fn, argnum);
 
       return cp_convert (totype, expr, complain);
     }
@@ -6987,9 +7020,7 @@ convert_like_real (conversion *convs, tree expr, tree fn, int argnum,
 		       ? LOOKUP_IMPLICIT : LOOKUP_NORMAL);
 	  build_user_type_conversion (totype, convs->u.expr, flags, complain);
 	  gcc_assert (seen_error ());
-	  if (fn)
-	    inform (DECL_SOURCE_LOCATION (fn),
-		    "  initializing argument %P of %qD", argnum, fn);
+	  maybe_inform_about_fndecl_for_bogus_argument_init (fn, argnum);
 	}
       return error_mark_node;
 
@@ -7083,9 +7114,7 @@ convert_like_real (conversion *convs, tree expr, tree fn, int argnum,
 	    {
 	      auto_diagnostic_group d;
 	      maybe_print_user_conv_context (convs);
-	      if (fn)
-		inform (DECL_SOURCE_LOCATION (fn),
-			"  initializing argument %P of %qD", argnum, fn);
+	      maybe_inform_about_fndecl_for_bogus_argument_init (fn, argnum);
 	    }
 	  return error_mark_node;
 	}
@@ -7136,9 +7165,7 @@ convert_like_real (conversion *convs, tree expr, tree fn, int argnum,
 	{
 	  auto_diagnostic_group d;
 	  maybe_print_user_conv_context (convs);
-	  if (fn)
-	    inform (DECL_SOURCE_LOCATION (fn),
-		    "  initializing argument %P of %qD", argnum, fn);
+	  maybe_inform_about_fndecl_for_bogus_argument_init (fn, argnum);
 	}
 
       return build_cplus_new (totype, expr, complain);
@@ -7165,9 +7192,8 @@ convert_like_real (conversion *convs, tree expr, tree fn, int argnum,
 	    else
 	      gcc_unreachable ();
 	    maybe_print_user_conv_context (convs);
-	    if (fn)
-	      inform (DECL_SOURCE_LOCATION (fn),
-		      "  initializing argument %P of %qD", argnum, fn);
+	    maybe_inform_about_fndecl_for_bogus_argument_init (fn, argnum);
+
 	    return error_mark_node;
 	  }
 
@@ -9299,8 +9325,8 @@ complain_about_bad_argument (location_t arg_loc,
   error_at (&richloc,
 	    "cannot convert %qH to %qI",
 	    from_type, to_type);
-  inform (get_fndecl_argument_location (fndecl, parmnum),
-	  "  initializing argument %P of %qD", parmnum, fndecl);
+  maybe_inform_about_fndecl_for_bogus_argument_init (fndecl,
+						     parmnum);
 }
 
 /* Subroutine of build_new_method_call_1, for where there are no viable
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 111a123..c1f9931 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -6145,6 +6145,7 @@ extern location_t get_fndecl_argument_location  (tree, int);
 extern void complain_about_bad_argument	(location_t arg_loc,
 						 tree from_type, tree to_type,
 						 tree fndecl, int parmnum);
+extern void maybe_inform_about_fndecl_for_bogus_argument_init (tree, int);
 
 
 /* A class for recording information about access failures (e.g. private
diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index ffc0d0d..265826a 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -48,6 +48,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "intl.h"
 #include "c-family/c-ada-spec.h"
 #include "asan.h"
+#include "gcc-rich-location.h"
 
 /* Id for dumping the raw trees.  */
 int raw_dump_id;
@@ -5179,14 +5180,25 @@ check_default_args (tree x)
 {
   tree arg = TYPE_ARG_TYPES (TREE_TYPE (x));
   bool saw_def = false;
+  location_t loc_of_first_default_arg = UNKNOWN_LOCATION;
   int i = 0 - (TREE_CODE (TREE_TYPE (x)) == METHOD_TYPE);
   for (; arg && arg != void_list_node; arg = TREE_CHAIN (arg), ++i)
     {
       if (TREE_PURPOSE (arg))
-	saw_def = true;
+	{
+	  saw_def = true;
+	  location_t loc = get_fndecl_argument_location (x, i);
+	  if (loc != DECL_SOURCE_LOCATION (x))
+	    loc_of_first_default_arg = loc;
+	}
       else if (saw_def && !PACK_EXPANSION_P (TREE_VALUE (arg)))
 	{
-	  error ("default argument missing for parameter %P of %q+#D", i, x);
+	  location_t loc = get_fndecl_argument_location (x, i);
+	  gcc_rich_location richloc (loc);
+	  if (loc_of_first_default_arg != UNKNOWN_LOCATION)
+	    richloc.add_range (loc_of_first_default_arg);
+	  error_at (&richloc,
+		    "default argument missing for parameter %P of %q#D", i, x);
 	  TREE_PURPOSE (arg) = error_mark_node;
 	}
     }
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index f45c06e..c3807de 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -4007,11 +4007,19 @@ convert_arguments (tree typelist, vec<tree, va_gc> **values, tree fndecl,
 	    {
               if (complain & tf_error)
                 {
+		  location_t loc = EXPR_LOC_OR_LOC (val, input_location);
                   if (fndecl)
-                    error ("parameter %P of %qD has incomplete type %qT",
-                           i, fndecl, type);
+		    {
+		      auto_diagnostic_group d;
+		      error_at (loc,
+				"parameter %P of %qD has incomplete type %qT",
+				i, fndecl, type);
+		      inform (get_fndecl_argument_location (fndecl, i),
+			      "  declared here");
+		    }
                   else
-                    error ("parameter %P has incomplete type %qT", i, type);
+		    error_at (loc, "parameter %P has incomplete type %qT", i,
+			      type);
                 }
 	      parmval = error_mark_node;
 	    }
@@ -8795,6 +8803,8 @@ convert_for_assignment (tree type, tree rhs,
   tree rhstype;
   enum tree_code coder;
 
+  location_t rhs_loc = EXPR_LOC_OR_LOC (rhs, input_location);
+
   /* Strip NON_LVALUE_EXPRs since we aren't using as an lvalue.  */
   if (TREE_CODE (rhs) == NON_LVALUE_EXPR)
     rhs = TREE_OPERAND (rhs, 0);
@@ -8901,7 +8911,7 @@ convert_for_assignment (tree type, tree rhs,
 						   parmnum, complain, flags);
 		}
 	      else if (fndecl)
-		complain_about_bad_argument (cp_expr_location (rhs),
+		complain_about_bad_argument (rhs_loc,
 					     rhstype, type,
 					     fndecl, parmnum);
 	      else
@@ -9068,6 +9078,7 @@ convert_for_initialization (tree exp, tree type, tree rhs, int flags,
 
   if (codel == REFERENCE_TYPE)
     {
+      auto_diagnostic_group d;
       /* This should eventually happen in convert_arguments.  */
       int savew = 0, savee = 0;
 
@@ -9077,9 +9088,8 @@ convert_for_initialization (tree exp, tree type, tree rhs, int flags,
 
       if (fndecl
 	  && (warningcount + werrorcount > savew || errorcount > savee))
-	inform (DECL_SOURCE_LOCATION (fndecl),
+	inform (get_fndecl_argument_location (fndecl, parmnum),
 		"in passing argument %P of %qD", parmnum, fndecl);
-
       return rhs;
     }
 
diff --git a/gcc/testsuite/g++.dg/diagnostic/missing-default-args.C b/gcc/testsuite/g++.dg/diagnostic/missing-default-args.C
new file mode 100644
index 0000000..f681842
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/missing-default-args.C
@@ -0,0 +1,53 @@
+// { dg-options "-fdiagnostics-show-caret" }
+
+/* Function.  */
+
+void test_1 (int a, int b = 42, int c, int d); // { dg-line test_1 }
+
+// { dg-error "default argument missing for parameter 3 of " "" { target *-*-* } test_1 }
+/* { dg-begin-multiline-output "" }
+ void test_1 (int a, int b = 42, int c, int d);
+                     ~~~~~~~~~~  ~~~~^
+   { dg-end-multiline-output "" } */
+
+// { dg-error "default argument missing for parameter 4 of " "" { target *-*-* } test_1 }
+/* { dg-begin-multiline-output "" }
+ void test_1 (int a, int b = 42, int c, int d);
+                     ~~~~~~~~~~         ~~~~^
+   { dg-end-multiline-output "" } */
+
+
+/* Non-static member fn.  */
+
+struct test_2
+{
+  void member_2 (int a, int b = 42, int c); // { dg-error "default argument missing for parameter 3 of " }
+};
+
+
+/* { dg-begin-multiline-output "" }
+   void member_2 (int a, int b = 42, int c);
+                         ~~~~~~~~~~  ~~~~^
+   { dg-end-multiline-output "" } */
+
+
+/* Static member fn.  */
+
+struct test_3
+{
+  static void member_3 (int a, int b = 42, int c); // { dg-error "default argument missing for parameter 3 of " }
+};
+/* { dg-begin-multiline-output "" }
+   static void member_3 (int a, int b = 42, int c);
+                                ~~~~~~~~~~  ~~~~^
+   { dg-end-multiline-output "" } */
+
+
+/* Template.  */
+
+template <typename Type>
+void test_4 (int a, int b = 42, int c); // { dg-error "default argument missing for parameter 3 of " }
+/* { dg-begin-multiline-output "" }
+ void test_4 (int a, int b = 42, int c);
+                     ~~~~~~~~~~  ~~~~^
+   { dg-end-multiline-output "" } */
diff --git a/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-3.C b/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-3.C
new file mode 100644
index 0000000..3ffbbd8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch-3.C
@@ -0,0 +1,26 @@
+// { dg-do compile { target c++14 } }
+// { dg-options "-fdiagnostics-show-caret" }
+
+void f2(int, char (*)(int), int) { } // { dg-line f2 }
+
+void test_1 ()
+{
+  auto glambda = [](auto a) { return a; }; // { dg-line candidate }
+  int (*fp)(int) = glambda;
+  f2(1, glambda, 3); // { dg-error "invalid user-defined conversion" }
+  /* { dg-begin-multiline-output "" }
+   f2(1, glambda, 3);
+         ^~~~~~~
+     { dg-end-multiline-output "" } */
+  // { dg-message "candidate is: " "" { target *-*-* } candidate }
+  /* { dg-begin-multiline-output "" }
+   auto glambda = [](auto a) { return a; };
+                  ^
+     { dg-end-multiline-output "" } */
+  // { dg-message "no known conversion from " "" { target *-*-* } candidate }
+  // { dg-message "initializing argument 2 of " "" { target *-*-* } f2 }
+  /* { dg-begin-multiline-output "" }
+ void f2(int, char (*)(int), int) { }
+              ^~~~~~~~~~~~~
+     { dg-end-multiline-output "" } */
+}
diff --git a/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch.C b/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch.C
index cb5c360..54ffb06 100644
--- a/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch.C
+++ b/gcc/testsuite/g++.dg/diagnostic/param-type-mismatch.C
@@ -224,4 +224,45 @@ int test_11 (int first, int second, float third)
      { dg-end-multiline-output "" } */
 }
 
+/* Bad reference.  */
+
+struct s12;
+
+extern int callee_12 (int one, s12 &second, float three); // { dg-line callee_12 }
+
+int test_12 (int first, int second, float third)
+{
+  return callee_12 (first, second, third); // { dg-error "invalid initialization of reference of " }
+  /* { dg-begin-multiline-output "" }
+   return callee_12 (first, second, third);
+                            ^~~~~~
+     { dg-end-multiline-output "" } */
+  // { dg-message "in passing argument 2 of " "" { target *-*-* } callee_12 }
+  /* { dg-begin-multiline-output "" }
+ extern int callee_12 (int one, s12 &second, float three);
+                                ~~~~~^~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+/* Incomplete type.  */
+
+struct s13;
+
+extern int callee_13 (int one, s13 second, float three); // { dg-line callee_13 }
+
+int test_13 (int first, int second, float third)
+{
+  return callee_13 (first, second, third); // { dg-error "has incomplete type" }
+  /* { dg-begin-multiline-output "" }
+   return callee_13 (first, second, third);
+                            ^~~~~~
+     { dg-end-multiline-output "" } */
+  // { dg-message "declared here" "" { target *-*-* } callee_13 }
+  /* { dg-begin-multiline-output "" }
+ extern int callee_13 (int one, s13 second, float three);
+                                ~~~~^~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+
 // TODO: template callsite
diff --git a/gcc/testsuite/g++.dg/warn/Wconversion-null-4.C b/gcc/testsuite/g++.dg/warn/Wconversion-null-4.C
new file mode 100644
index 0000000..465dc5a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wconversion-null-4.C
@@ -0,0 +1,43 @@
+// { dg-do compile  }
+// { dg-options "-Wconversion-null -fdiagnostics-show-caret" }
+
+#include <stddef.h>
+
+void callee_1 (int, int, int) {} // { dg-message "declared here" }
+
+void caller_1 (void)
+{
+  callee_1 (0, NULL, 2); // { dg-warning "passing NULL to non-pointer argument 2 of" }
+  /* { dg-begin-multiline-output "" }
+   callee_1 (0, NULL, 2);
+                ^~~~
+     { dg-end-multiline-output "" } */
+  /* { dg-begin-multiline-output "" }
+ void callee_1 (int, int, int) {}
+                     ^~~
+     { dg-end-multiline-output "" } */
+}
+
+void callee_2 (int, void *, int) {} // { dg-message "declared here" "" { target { ! c++11 } } }
+// { dg-message "initializing argument 2 of " "" { target c++11 } .-1 }
+
+void caller_2 (void)
+{
+  callee_2 (0, false, 2); // { dg-warning "converting 'false' to pointer type for argument 2 of " "" { target { ! c++11 } } }
+  // { dg-error "cannot convert" "" { target c++11 } .-1 }
+
+  /* { dg-begin-multiline-output "" }
+   callee_2 (0, false, 2);
+                ^~~~~
+     { dg-end-multiline-output "" { target { ! c++11 } } } */
+  /* { dg-begin-multiline-output "" }
+   callee_2 (0, false, 2);
+                ^~~~~
+                |
+                bool
+     { dg-end-multiline-output "" { target c++11 } } */
+  /* { dg-begin-multiline-output "" }
+ void callee_2 (int, void *, int) {}
+                     ^~~~~~
+     { dg-end-multiline-output "" } */
+}
-- 
1.8.5.3


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