MatCat.OpenSource/8sa1-gcc
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

c++: constrained CTAD for nested class template [PR97679]

Browse Source 
In the testcase below, we're crashing during constraint checking of the
implicitly generated deduction guides for the nested class template A::B
because we never substitute the outer template arguments (for A) into
the constraint, neither ahead of time nor as part of satisfaction.

Ideally we'd like to avoid substituting into a constraint ahead of
time, but the "flattening" vector 'tsubst_args' is constructed under the
assumption that all outer template arguments are already substituted in,
and eliminating this assumption to yield a flattening vector that
includes outer (generic) template arguments suitable for substituting
into the constraint would be tricky and error-prone.  So this patch
takes the approximate approach of substituting the outer arguments into
the constraint ahead of time, so that the subsequent substitution of
'tsubst_args' is coherent and so later satisfaction just works.

gcc/cp/ChangeLog:

	PR c++/97679
	* pt.c (build_deduction_guide): Document OUTER_ARGS.  Substitute
	them into the propagated constraints.

gcc/testsuite/ChangeLog:

	PR c++/97679
	* g++.dg/cpp2a/concepts-ctad3.C: New test.
This commit is contained in:
Patrick Palka 2021-04-08 13:07:37 -04:00
parent 0567998287
commit 05708d6eef
2 changed files with 33 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
gcc/cp/pt.c
View File

@ -28602,7 +28602,8 @@ rewrite_tparm_list (tree oldelt, unsigned index, unsigned level,
/* Returns a C++17 class deduction guide template based on the constructor
CTOR. As a special case, CTOR can be a RECORD_TYPE for an implicit default
guide, REFERENCE_TYPE for an implicit copy/move guide, or TREE_LIST for an
aggregate initialization guide. */
aggregate initialization guide. OUTER_ARGS are the template arguments
for the enclosing scope of the class. */
static tree
build_deduction_guide (tree type, tree ctor, tree outer_args, tsubst_flags_t complain)
@ -28728,7 +28729,15 @@ build_deduction_guide (tree type, tree ctor, tree outer_args, tsubst_flags_t com
if (fparms == error_mark_node)
ok = false;
if (ci)
ci = tsubst_constraint_info (ci, tsubst_args, complain, ctor);
{
if (outer_args)
/* FIXME: We'd like to avoid substituting outer template
arguments into the constraint ahead of time, but the
construction of tsubst_args assumes that outer arguments
are already substituted in. */
ci = tsubst_constraint_info (ci, outer_args, complain, ctor);
ci = tsubst_constraint_info (ci, tsubst_args, complain, ctor);
}
/* Parms are to have DECL_CHAIN tsubsted, which would be skipped if
cp_unevaluated_operand. */
@ -28744,7 +28753,12 @@ build_deduction_guide (tree type, tree ctor, tree outer_args, tsubst_flags_t com
fparms = tsubst_arg_types (fparms, targs, NULL_TREE, complain, ctor);
fargs = tsubst (fargs, targs, complain, ctor);
if (ci)
ci = tsubst_constraint_info (ci, targs, complain, ctor);
{
if (outer_args)
/* FIXME: As above. */
ci = tsubst_constraint_info (ci, outer_args, complain, ctor);
ci = tsubst_constraint_info (ci, targs, complain, ctor);
}
}
--processing_template_decl;

16
gcc/testsuite/g++.dg/cpp2a/concepts-ctad3.C Normal file
View File

@ -0,0 +1,16 @@
// PR c++/97679
// { dg-do compile { target c++20 } }
template <bool V> struct A {
template <class T> struct B {
B(T) requires V;
template <class U> B(T, U) requires V || (__is_same(T, char) && __is_same(U, int));
};
};
A<true>::B x1(0);
A<false>::B x2(0); // { dg-error "deduction|no match" }
A<true>::B y1(0, '0');
A<false>::B y2(0, '0'); // { dg-error "deduction|no match" }
A<false>::B y3('0', 0);