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c++: naming a dependently-scoped template for CTAD [PR104641]

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In order to be able to perform CTAD for a dependently-scoped template
(such as A<T>::B in the testcase below), we need to permit a
typename-specifier to resolve to a template as per [dcl.type.simple]/3,
at least when it appears in a CTAD-enabled context.

This patch implements this using a new tsubst flag tf_tst_ok to control
when a TYPENAME_TYPE is allowed to name a template, and sets this flag
when substituting into the type of a CAST_EXPR, CONSTRUCTOR or VAR_DECL
(each of which is a CTAD-enabled context).

	PR c++/104641

gcc/cp/ChangeLog:

	* cp-tree.h (tsubst_flags::tf_tst_ok): New flag.
	* decl.cc (make_typename_type): Allow a typename-specifier to
	resolve to a template when tf_tst_ok, in which case return
	a CTAD placeholder for the template.
	* pt.cc (tsubst_decl) <case VAR_DECL>: Set tf_tst_ok when
	substituting the type.
	(tsubst): Clear tf_tst_ok and remember if it was set.
	<case TYPENAME_TYPE>: Pass tf_tst_ok to make_typename_type
	appropriately.
	(tsubst_copy) <case CAST_EXPR>: Set tf_tst_ok when substituting
	the type.
	(tsubst_copy_and_build) <case CAST_EXPR>: Likewise.
	<case CONSTRUCTOR>: Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/class-deduction107.C: New test.
This commit is contained in:
Patrick Palka 2022-03-12 15:00:51 -05:00
parent 03c83cf7aa
commit d3b0dc686c
4 changed files with 63 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
gcc/cp/cp-tree.h
View file

@ -5563,6 +5563,8 @@ enum tsubst_flags {
(build_target_expr and friends) */
tf_norm = 1 << 11, /* Build diagnostic information during
constraint normalization. */
tf_tst_ok = 1 << 12, /* Allow a typename-specifier to name
a template (C++17 or later). */
/* Convenient substitution flags combinations. */
tf_warning_or_error = tf_warning | tf_error
};

18
gcc/cp/decl.cc
View file

@ -4204,16 +4204,26 @@ make_typename_type (tree context, tree name, enum tag_types tag_type,
}
if (!want_template && TREE_CODE (t) != TYPE_DECL)
{
if (complain & tf_error)
error ("%<typename %T::%D%> names %q#T, which is not a type",
context, name, t);
return error_mark_node;
if ((complain & tf_tst_ok) && cxx_dialect >= cxx17
&& DECL_TYPE_TEMPLATE_P (t))
/* The caller permits this typename-specifier to name a template
(because it appears in a CTAD-enabled context). */;
else
{
if (complain & tf_error)
error ("%<typename %T::%D%> names %q#T, which is not a type",
context, name, t);
return error_mark_node;
}
}
if (!check_accessibility_of_qualified_id (t, /*object_type=*/NULL_TREE,
context, complain))
return error_mark_node;
if (!want_template && DECL_TYPE_TEMPLATE_P (t))
return make_template_placeholder (t);
if (want_template)
{
t = lookup_template_class (t, TREE_OPERAND (fullname, 1),

29
gcc/cp/pt.cc
View file

@ -14896,7 +14896,10 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
&& VAR_HAD_UNKNOWN_BOUND (t)
&& type != error_mark_node)
type = strip_array_domain (type);
type = tsubst (type, args, complain, in_decl);
tsubst_flags_t tcomplain = complain;
if (VAR_P (t))
tcomplain |= tf_tst_ok;
type = tsubst (type, args, tcomplain, in_decl);
/* Substituting the type might have recursively instantiated this
same alias (c++/86171). */
if (gen_tmpl && DECL_ALIAS_TEMPLATE_P (gen_tmpl)
@ -15582,6 +15585,9 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
bool fndecl_type = (complain & tf_fndecl_type);
complain &= ~tf_fndecl_type;
bool tst_ok = (complain & tf_tst_ok);
complain &= ~tf_tst_ok;
if (type
&& code != TYPENAME_TYPE
&& code != TEMPLATE_TYPE_PARM
@ -16169,8 +16175,10 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
return error_mark_node;
}
f = make_typename_type (ctx, f, typename_type,
complain | tf_keep_type_decl);
tsubst_flags_t tcomplain = complain | tf_keep_type_decl;
if (tst_ok)
tcomplain |= tf_tst_ok;
f = make_typename_type (ctx, f, typename_type, tcomplain);
if (f == error_mark_node)
return f;
if (TREE_CODE (f) == TYPE_DECL)
@ -17077,7 +17085,10 @@ tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl)
case CONVERT_EXPR:
case NOP_EXPR:
{
tree type = tsubst (TREE_TYPE (t), args, complain, in_decl);
tsubst_flags_t tcomplain = complain;
if (code == CAST_EXPR)
tcomplain |= tf_tst_ok;
tree type = tsubst (TREE_TYPE (t), args, tcomplain, in_decl);
tree op0 = tsubst_copy (TREE_OPERAND (t, 0), args, complain, in_decl);
return build1 (code, type, op0);
}
@ -20100,7 +20111,10 @@ tsubst_copy_and_build (tree t,
tree type;
tree op, r = NULL_TREE;
type = tsubst (TREE_TYPE (t), args, complain, in_decl);
tsubst_flags_t tcomplain = complain;
if (TREE_CODE (t) == CAST_EXPR)
tcomplain |= tf_tst_ok;
type = tsubst (TREE_TYPE (t), args, tcomplain, in_decl);
if (integral_constant_expression_p
&& !cast_valid_in_integral_constant_expression_p (type))
{
@ -21060,12 +21074,15 @@ tsubst_copy_and_build (tree t,
vec<constructor_elt, va_gc> *n;
constructor_elt *ce;
unsigned HOST_WIDE_INT idx;
tree type = tsubst (TREE_TYPE (t), args, complain, in_decl);
bool process_index_p;
int newlen;
bool need_copy_p = false;
tree r;
tsubst_flags_t tcomplain = complain;
if (COMPOUND_LITERAL_P (t))
tcomplain |= tf_tst_ok;
tree type = tsubst (TREE_TYPE (t), args, tcomplain, in_decl);
if (type == error_mark_node)
RETURN (error_mark_node);

24
gcc/testsuite/g++.dg/cpp1z/class-deduction107.C Normal file
View file

@ -0,0 +1,24 @@
// PR c++/104641
// { dg-do compile { target c++11 } }
template<class T>
struct A {
template<class U> struct B { B(U); };
private:
template<class U> struct C { C(U); };
};
template<class T>
void f() {
typename A<T>::B x = 0;
auto y = typename A<T>::B(0);
auto z = typename A<T>::B{0};
typename A<T>::C w(0); // { dg-error "private" "" { target c++17 } }
}
template void f<void>();
// { dg-error "not a type" "" { target c++14_down } 13 }
// { dg-error "not a type" "" { target c++14_down } 14 }
// { dg-error "not a type" "" { target c++14_down } 15 }
// { dg-error "not a type" "" { target c++14_down } 16 }