Re: [PATCH] Add gnu::diagnose_as attribute

[Matthias Kretz <m.kretz@gsi.de>]

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> On Tuesday, 4 May 2021 15:34:13 CEST David Malcolm wrote:
> > Does the patch interact correctly with the %H and %I codes that try to
> > show the differences between two template types?

While looking into this, I noticed that given

namespace std {
  struct A {};
  typedef A B;
}

const std::B would print as "'const B' {aka 'const std::A'}", i.e. without 
printing the scope of the typedef. I traced it to cp/error.c (dump_type). In 
the `if (TYPE_P (t) && typedef_variant_p (t))` branch, in the final else 
branch only cv-qualifiers and identifier are printed:

  pp_cxx_cv_qualifier_seq (pp, t);
  pp_cxx_tree_identifier (pp, TYPE_IDENTIFIER (t));

I believe the following should go in between, correct?

  pp_cxx_cv_qualifier_seq (pp, t);
  if (! (flags & TFF_UNQUALIFIED_NAME))
    dump_scope (pp, CP_DECL_CONTEXT (TYPE_NAME (t)), flags);
  pp_cxx_tree_identifier (pp, TYPE_IDENTIFIER (t));

This is important for my diagnose_as patch because otherwise the output is:

  'const string' {aka 'const std::string'}

which is confusing and unnecessarily verbose. Patch below.


From: Matthias Kretz <kretz@kde.org>

dump_type on 'const std::string' should not print 'const string' unless
TFF_UNQUALIFIED_NAME is requested.

gcc/cp/ChangeLog:
	* error.c: Call dump_scope when printing a typedef.
---
 gcc/cp/error.c | 2 ++
 1 file changed, 2 insertions(+)


-- 
──────────────────────────────────────────────────────────────────────────
 Dr. Matthias Kretz                           https://mattkretz.github.io
 GSI Helmholtz Centre for Heavy Ion Research               https://gsi.de
 std::experimental::simd              https://github.com/VcDevel/std-simd
──────────────────────────────────────────────────────────────────────────

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diff --git a/gcc/cp/error.c b/gcc/cp/error.c
index 10b547afaa7..edeaad44bcd 100644
--- a/gcc/cp/error.c
+++ b/gcc/cp/error.c
@@ -511,6 +511,8 @@ dump_type (cxx_pretty_printer *pp, tree t, int flags)
       else
 	{
 	  pp_cxx_cv_qualifier_seq (pp, t);
+	  if (! (flags & TFF_UNQUALIFIED_NAME))
+	    dump_scope (pp, CP_DECL_CONTEXT (TYPE_NAME (t)), flags);
 	  pp_cxx_tree_identifier (pp, TYPE_IDENTIFIER (t));
 	  return;
 	}