c++/reflection: splice parsing fixes [PR123823]

This patch fixes the problem that when cp_parser_splice_specifier sees
:]<, it always thinks it's a template-id.  Consequently, this should compile
but does not:

  int i;
  constexpr auto r = ^^i;
  bool b = [:r:] < 42;

because we think that a template argument list follows the splice.

Fixed by implementing [temp.names]/3 better: only attempt to parse
a template argument list if we saw template or typename.  As an
extension, also parse a template argument list if the splice yielded
a TEMPLATE_DECL -- in that case, chances are that the user simply
forgot to specify 'template'.  In that case we'll suggest adding
'template' in cp_parser_splice_expression.

We should accept the following given [temp.names]/3:

  S<[:r:] < 43> s;

and we should also accept:

  [:r:] < 42 > 0;

I also realized that my code to detect unparenthesized splice
expressions as template arguments is wrong.  [expr.prim.splice] says that

  constexpr auto i = e<[:^^h:]>;

is ill-formed, but "S<[:r:] >= 1>" is fine as per [temp.names]/6.  I moved
the checking to cp_parser_template_argument while making sure that we
only complain when the splice-expression is the whole template-argument.

This patch also fixes 123640.

	PR c++/123823
	PR c++/123640

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_splice_specifier): New typename_p parameter.
	Use cp_parser_nth_token_starts_template_argument_list_p instead of
	checking CPP_LESS.  Check for typename/template/TEMPLATE_DECL before
	parsing a template-id.
	(cp_parser_splice_type_specifier): Adjust the call to
	cp_parser_splice_specifier.
	(cp_parser_splice_expression): Don't detect unparenthesized splice
	expressions here.  Adjust the call to cp_parser_splice_specifier.
	(cp_parser_splice_scope_specifier): Adjust the call to
	cp_parser_splice_specifier.
	(cp_parser_skip_entire_splice_expr): New, broken out of...
	(cp_parser_splice_spec_is_nns_p): ...this.
	(cp_parser_template_id): Call pop_deferring_access_checks.
	(cp_parser_template_argument): Detect unparenthesized splice
	expressions here.

gcc/testsuite/ChangeLog:

	* g++.dg/reflect/crash6.C: Adjust expected diagnostic.
	* g++.dg/reflect/expr3.C: Likewise.  Test more cases.
	* g++.dg/reflect/splice4.C: Adjust expected diagnostic.
	* g++.dg/reflect/error12.C: New test.
	* g++.dg/reflect/parse1.C: New test.
	* g++.dg/reflect/parse2.C: New test.
	* g++.dg/reflect/parse3.C: New test.
	* g++.dg/reflect/parse4.C: New test.
	* g++.dg/reflect/parse5.C: New test.
	* g++.dg/reflect/parse6.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>

0 files changed, 0 insertions, 0 deletions