c++: Fix parsing [[]][[]];

When working on the previous patch I put [[]] [[]] asm (""); into a
testcase, but was surprised it wasn't parsed.
The problem is that when cp_parser_std_attribute_spec returns NULL, it
can mean 2 different things, one is that the next token(s) are neither
[[ nor alignas (in that case the caller should break from the loop),
or when we parsed something like [[]] - it was valid attribute specifier,
but didn't specify any attributes in it.

The following patch fixes that by using a magic value of void_list_node
for the case where the first tokens are neither [[ nor alignas and so
where cp_parser_std_attribute_spec_seq should stop iterating to differentiate
it from NULL_TREE which stands for some attribute specifier has been parsed,
but it didn't contain any (or any valid) attributes.

2023-12-08  Jakub Jelinek  <jakub@redhat.com>

	* parser.cc (cp_parser_std_attribute_spec): Return void_list_node
	rather than NULL_TREE if token is neither CPP_OPEN_SQUARE nor
	RID_ALIGNAS CPP_KEYWORD.
	(cp_parser_std_attribute_spec_seq): For attr_spec == void_list_node
	break, for attr_spec == NULL_TREE continue.

	* g++.dg/cpp0x/gen-attrs-79.C: New test.

0 files changed, 0 insertions, 0 deletions