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c++: Fix specialization of constrained member template.

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The resolution of comment CA104 clarifies that we need to do direct
substitution of constraints in order to determine which member template
corresponds to an explicit specialization.

gcc/cp/ChangeLog
2020-05-11  Jason Merrill  <jason@redhat.com>

	Resolve C++20 NB comment CA104
	* pt.c (determine_specialization): Compare constraints for
	specialization of member template of class instantiation.
This commit is contained in:
Jason Merrill 2020-05-11 15:46:59 -04:00
parent 0f50f6daa1
commit 52c5933f58
4 changed files with 42 additions and 4 deletions
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6
gcc/cp/ChangeLog
View File

@ -1,3 +1,9 @@
2020-05-11 Jason Merrill <jason@redhat.com>
Resolve C++20 NB comment CA104
* pt.c (determine_specialization): Compare constraints for
specialization of member template of class instantiation.
2020-05-11 Jason Merrill <jason@redhat.com>
PR c++/92583

28
gcc/cp/pt.c
View File

@ -2282,8 +2282,29 @@ determine_specialization (tree template_id,
below. */
if (tsk == tsk_template)
{
if (compparms (fn_arg_types, decl_arg_types))
candidates = tree_cons (NULL_TREE, fn, candidates);
if (!comp_template_parms (DECL_TEMPLATE_PARMS (fn),
current_template_parms))
continue;
if (!same_type_p (TREE_TYPE (TREE_TYPE (decl)),
TREE_TYPE (TREE_TYPE (fn))))
continue;
if (!compparms (fn_arg_types, decl_arg_types))
continue;
tree freq = get_trailing_function_requirements (fn);
tree dreq = get_trailing_function_requirements (decl);
if (!freq != !dreq)
continue;
if (freq)
{
tree fargs = DECL_TI_ARGS (fn);
tsubst_flags_t complain = tf_none;
freq = tsubst_constraint (freq, fargs, complain, fn);
if (!cp_tree_equal (freq, dreq))
continue;
}
candidates = tree_cons (NULL_TREE, fn, candidates);
continue;
}
@ -2472,7 +2493,8 @@ determine_specialization (tree template_id,
*targs_out = copy_node (DECL_TI_ARGS (fn));
/* Propagate the candidate's constraints to the declaration. */
set_constraints (decl, get_constraints (fn));
if (tsk != tsk_template)
set_constraints (decl, get_constraints (fn));
/* DECL is a re-declaration or partial instantiation of a template
function. */

10
gcc/testsuite/g++.dg/cpp2a/concepts-spec1.C Normal file
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@ -0,0 +1,10 @@
// Example from CA 104 proposal.
// { dg-do compile { target concepts } }
template <class T> concept C = sizeof(T) == 8;
template <class T> struct A {
template <class U> U f(U) requires C<typename T::type>; // #1
template <class U> U f(U) requires C<T>; // #2
};
template <> template <class U> U A<int>::f(U) requires C<int> { } // OK, specializes #2

2
gcc/testsuite/g++.dg/template/nontype18.C
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@ -5,4 +5,4 @@ template<int I> struct A
template<typename T> void foo();
};
template<int I> template<typename T> void A<0>::foo() {} // { dg-error "template parameter" }
template<int I> template<typename T> void A<0>::foo() {} // { dg-error "" }