On Wed, 2019-11-20 at 00:38 +0100, Jakub Jelinek wrote:
> 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.
I added complain_about_bad_argument in r264250 (aka
b78e49d1ddf1a09e16152353b41bf7c0b44d6405); the intent is to special-
case when there's a single candidate due to a bad argument, underlining
the pertinent bogus argument at the callsite, rather than having the
caret at the final close-paren of the call.
But it looks like I forgot about the "this" case. Does it make more
sense for pr90767-1.C to reject the special-casing if conv->n_arg is -1
for the "this"? (either in
complain_about_no_candidates_for_method_call, or in
maybe_get_bad_conversion_for_unmatched_call); perhaps like this:
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 0034c1c..eefb7ab 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -9855,16 +9855,18 @@ complain_about_no_candidates_for_method_call (tree
instance,
else
{
/* Special-case for when there's a single candidate that's failing
- due to a bad argument type. */
+ due to a bad argument type (but not for the "this" argument),
+ so that we can underline the pertinent argument at the callsite. */
if (z_candidate *candidate = single_z_candidate (candidates))
if (const conversion_info *conv
= maybe_get_bad_conversion_for_unmatched_call (candidate))
- {
- complain_about_bad_argument (conv->loc,
- conv->from, conv->to_type,
- candidate->fn, conv->n_arg);
- return;
- }
+ if (conv->n_arg != -1)
+ {
+ complain_about_bad_argument (conv->loc,
+ conv->from, conv->to_type,
+ candidate->fn, conv->n_arg);
+ return;
+ }
tree arglist = build_tree_list_vec (user_args);
tree errname = name;
(caveat: barely tested)
Dave
> In any case, I think the patch below is a step in the right
> direction.
>
> 2019-11-19 Jakub Jelinek <ja...@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
