[C++ Patch] PR 51786

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,

we got a couple of duplicates of this. The issue is that things like:

struct A {};
void foo() { decltype(A()); }

are turned by finish_decltype_type, called by 
cp_parser_simple_declaration via cp_parser_decl_specifier_seq, into 
something like:

struct A {};
void foo() { struct A; }

and later check_tag_decl, called via shadow_tag, doesn't see anything 
wrong wrt [dcl.dcl]/3, to wit doesn't see a declaration which doesn't 
declare anything. "Luckily" we have declares_class_or_enum available and 
we can query it to figure out whether a diagnostic is in fact in order.

Tested x86_64-linux.

Thanks,
Paolo.

PS: in fact we issue a permerror, not an error: I did some tests and I 
don't think that unconditionally zeroing the type even if we end up only 
emitting a warning can cause problems. But please double check, thanks!

//////////////////////////////

Attachment: CL_51786
Description: Text document

Attachment: patch_51786
Description: Text document