[C++ PATCH] Fix weird addr_expr not supported by dump_expr messages (PR c++/90767)

[Jakub Jelinek]

Hi!

The following patch is a minimal fix to avoid
cannot convert ‘‘addr_expr’ not supported by dump_type<type error>’ to ‘X*’
and similar messages.  The recently added complain_about_bad_argument
function expects a from_type argument, but conv->from isn't necessarily a
type, it can be an expression too.

With this patch one gets error like:
cannot convert ‘const X*’ to ‘X*’
and note like
initializing argument 'this' of ‘void X::foo()’
Still, perhaps what GCC 8 and earlier used to emit might be clearer:
pr90767-1.C: In member function ‘X::operator T() const’:
pr90767-1.C:12:7: error: no matching function for call to ‘X::foo() const’
pr90767-1.C:6:8: note: candidate: ‘void X::foo()’ <near match>
pr90767-1.C:6:8: note:   passing ‘const X*’ as ‘this’ argument discards qualifiers
There is the print_conversion_rejection function that handles the various
cases, like this vs. other arguments, conv->from with expr type vs. type
etc.
Though, I must say I don't understand the reasons why complain_about_bad_argument
has been added and whether we'd want to emit there what
print_conversion_rejection prints as notes with 2 leading spaces instead as
errors with no leading spaces.

In any case, I think the patch below is a step in the right direction.

2019-11-19  Jakub Jelinek  <jakub@redhat.com>

	PR c++/90767
	* call.c (complain_about_no_candidates_for_method_call): If
	conv->from is not a type, pass to complain_about_bad_argument
	lvalue_type of conv->from.

	* g++.dg/diagnostic/pr90767-1.C: New test.
	* g++.dg/diagnostic/pr90767-2.C: New test.

--- gcc/cp/call.c.jj	2019-11-18 18:49:14.461880924 +0100
+++ gcc/cp/call.c	2019-11-19 14:40:19.121937148 +0100
@@ -9861,8 +9861,11 @@ complain_about_no_candidates_for_method_
 	  if (const conversion_info *conv
 		= maybe_get_bad_conversion_for_unmatched_call (candidate))
 	    {
+	      tree from_type = conv->from;
+	      if (!TYPE_P (conv->from))
+		from_type = lvalue_type (conv->from);
 	      complain_about_bad_argument (conv->loc,
-					   conv->from, conv->to_type,
+					   from_type, conv->to_type,
 					   candidate->fn, conv->n_arg);
 	      return;
 	    }
--- gcc/testsuite/g++.dg/diagnostic/pr90767-1.C.jj	2019-11-19 14:48:00.386041586 +0100
+++ gcc/testsuite/g++.dg/diagnostic/pr90767-1.C	2019-11-19 14:46:53.395043036 +0100
@@ -0,0 +1,15 @@
+// PR c++/90767
+// { dg-do compile }
+
+struct X {
+  int n;
+  void foo ();	// { dg-message "initializing argument 'this'" }
+
+  template<typename T>
+  operator T () const
+    {
+      if (n == 0)
+	foo ();	// { dg-error "cannot convert 'const X\\*' to 'X\\*'" }
+      return n;
+    }
+};
--- gcc/testsuite/g++.dg/diagnostic/pr90767-2.C.jj	2019-11-19 14:50:48.923522136 +0100
+++ gcc/testsuite/g++.dg/diagnostic/pr90767-2.C	2019-11-19 14:52:27.324051149 +0100
@@ -0,0 +1,15 @@
+// PR c++/90767
+// { dg-do compile }
+
+struct A {
+  struct B { B (int) {} };
+
+  template <typename T>
+  void foo ()
+  {
+    int x = 0;
+    bar (x);	// { dg-error "cannot convert 'int' to 'A::B&'" }
+  }
+
+  void bar (B &arg) {}	// { dg-message "initializing argument 1" }
+};

	Jakub