We already have generic support for predicate-like traits that yield a
boolean value via TRAIT_EXPR, but we lack the same support for traits
that yield a type instead of a value. Such support would streamline
implementing efficient builtins for the standard library type traits.
To that end this patch implements a generic TRAIT_TYPE type alongside
TRAIT_EXPR, and reimplements the existing UNDERLYING_TYPE builtin trait
using this new TRAIT_TYPE.
gcc/cp/ChangeLog:
* cp-objcp-common.cc (cp_common_init_ts): Replace
UNDERLYING_TYPE with TRAIT_TYPE.
* cp-tree.def (TRAIT_TYPE): Define.
(UNDERLYING_TYPE): Remove.
* cp-tree.h (TRAIT_TYPE_KIND_RAW): Define.
(TRAIT_TYPE_KIND): Define.
(TRAIT_TYPE_TYPE1): Define.
(TRAIT_TYPE_TYPE2): Define.
(WILDCARD_TYPE_P): Return true for TRAIT_TYPE.
(finish_trait_type): Declare.
* cxx-pretty-print.cc (cxx_pretty_printer::primary_expression):
Adjust after renaming pp_cxx_trait_expression.
(cxx_pretty_printer::simple_type_specifier) <case TRAIT_TYPE>:
New.
(cxx_pretty_printer::type_id): Replace UNDERLYING_TYPE with
TRAIT_TYPE.
(pp_cxx_trait_expression): Rename to ...
(pp_cxx_trait): ... this. Handle TRAIT_TYPE as well. Correct
pretty printing of the trailing arguments.
* cxx-pretty-print.h (pp_cxx_trait_expression): Rename to ...
(pp_cxx_trait_type): ... this.
* error.cc (dump_type) <case UNDERLYING_TYPE>: Remove.
<case TRAIT_TYPE>: New.
(dump_type_prefix): Replace UNDERLYING_WITH with TRAIT_TYPE.
(dump_type_suffix): Likewise.
* mangle.cc (write_type) <case UNDERLYING_TYPE>: Remove.
<case TRAIT_TYPE>: New.
* module.cc (trees_out::type_node) <case UNDERLYING_TYPE>:
Remove.
<case TRAIT_TYPE>: New.
(trees_in::tree_node): Likewise.
* parser.cc (cp_parser_primary_expression): Adjust after
renaming cp_parser_trait_expr.
(cp_parser_trait_expr): Rename to ...
(cp_parser_trait): ... this. Call finish_trait_type for traits
that yield a type.
(cp_parser_simple_type_specifier): Adjust after renaming
cp_parser_trait_expr.
* pt.cc (for_each_template_parm_r) <case UNDERLYING_TYPE>:
Remove.
<case TRAIT_TYPE>: New.
(tsubst): Likewise.
(unify): Replace UNDERLYING_TYPE with TRAIT_TYPE.
(dependent_type_p_r): Likewise.
* semantics.cc (finish_underlying_type): Don't return
UNDERLYING_TYPE anymore when processing_template_decl.
(finish_trait_type): Define.
* tree.cc (strip_typedefs) <case UNDERLYING_TYPE>: Remove.
<case TRAIT_TYPE>: New.
(cp_walk_subtrees): Likewise.
* typeck.cc (structural_comptypes): Likewise.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/alias-decl-59.C: Adjust expected error message.
* g++.dg/ext/underlying_type7.C: Likewise.
* g++.dg/ext/underlying_type13.C: New test.
* g++.dg/ext/underlying_type14.C: New test.