c++/modules: member alias tmpl partial inst [PR103994]

Alias templates are weird in that their specializations can appear in
both decl_specializations and type_specializations.  They're always in
the decl table, and additionally appear in the type table only at parse
time via finish_template_type.  There seems to be no good reason for
them to appear in both tables, and the code paths end up stepping over
each other in particular for a partial instantiation such as
A<B>::key_arg<T> in the below modules testcase: the type code path
(lookup_template_class) wants to set TI_TEMPLATE to the most general
template whereas the decl code path (tsubst_template_decl called during
instantiation of A<B>) already set TI_TEMPLATE to the partially
instantiated TEMPLATE_DECL.  This TI_TEMPLATE change ends up confusing
modules which decides to stream the logically equivalent TYPE_DECL and
TEMPLATE_DECL for this partial instantiation separately.

This patch fixes this by making lookup_template_class dispatch to
instantiate_alias_template early for alias template specializations.
In turn we now add such specializations only to the decl table.  This
admits some nice simplification in the modules code which otherwise has
to cope with such specializations appearing in both tables.

	PR c++/103994

gcc/cp/ChangeLog:

	* cp-tree.h (add_mergeable_specialization): Remove second
	parameter.
	* module.cc (depset::disc_bits::DB_ALIAS_TMPL_INST_BIT): Remove.
	(depset::disc_bits::DB_ALIAS_SPEC_BIT): Remove.
	(depset::is_alias_tmpl_inst): Remove.
	(depset::is_alias): Remove.
	(merge_kind::MK_tmpl_alias_mask): Remove.
	(merge_kind::MK_alias_spec): Remove.
	(merge_kind_name): Remove entries for alias specializations.
	(trees_out::core_vals) <case TEMPLATE_DECL>: Adjust after
	removing is_alias_tmpl_inst.
	(trees_in::decl_value): Adjust add_mergeable_specialization
	calls.
	(trees_out::get_merge_kind) <case depset::EK_SPECIALIZATION>:
	Use MK_decl_spec for alias template specializations.
	(trees_out::key_mergeable): Simplify after MK_tmpl_alias_mask
	removal.
	(depset::hash::make_dependency): Adjust after removing
	DB_ALIAS_TMPL_INST_BIT.
	(specialization_add): Don't allow alias templates when !decl_p.
	(depset::hash::add_specializations): Remove now-dead code
	accomodating alias template specializations in the type table.
	* pt.cc (lookup_template_class): Dispatch early to
	instantiate_alias_template for alias templates.  Simplify
	accordingly.
	(add_mergeable_specialization): Remove alias_p parameter and
	simplify accordingly.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/pr99425-1_b.H: s/alias/decl in dump scan.
	* g++.dg/modules/tpl-alias-1_a.H: Likewise.
	* g++.dg/modules/tpl-alias-2_a.H: New test.
	* g++.dg/modules/tpl-alias-2_b.C: New test.

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

0 files changed, 0 insertions, 0 deletions