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c++: variadic lambda template and empty pack [PR97246]

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In get<0>, Is is empty, so the first parameter pack of the lambda is empty,
but after the fix for PR94546 we were wrongly associating it with the
partial instantiation of 'v'.

gcc/cp/ChangeLog:

	PR c++/97246
	PR c++/94546
	* pt.c (extract_fnparm_pack): Check DECL_PACK_P here.
	(register_parameter_specializations): Not here.

gcc/testsuite/ChangeLog:

	PR c++/97246
	* g++.dg/cpp2a/lambda-generic-variadic21.C: New test.
This commit is contained in:
Jason Merrill 2021-02-11 19:45:22 -05:00
parent 3e2f329e94
commit ac001ddd0c
2 changed files with 43 additions and 14 deletions
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38
gcc/cp/pt.c
View File

@ -12302,29 +12302,40 @@ extract_fnparm_pack (tree tmpl_parm, tree *spec_p)
{
/* Collect all of the extra "packed" parameters into an
argument pack. */
tree parmvec;
tree argpack = make_node (NONTYPE_ARGUMENT_PACK);
tree argpack;
tree spec_parm = *spec_p;
int i, len;
int len;
for (len = 0; spec_parm; ++len, spec_parm = TREE_CHAIN (spec_parm))
if (tmpl_parm
&& !function_parameter_expanded_from_pack_p (spec_parm, tmpl_parm))
break;
/* Fill in PARMVEC and PARMTYPEVEC with all of the parameters. */
parmvec = make_tree_vec (len);
spec_parm = *spec_p;
for (i = 0; i < len; i++, spec_parm = DECL_CHAIN (spec_parm))
if (len == 1 && DECL_PACK_P (spec_parm))
{
tree elt = spec_parm;
if (DECL_PACK_P (elt))
elt = make_pack_expansion (elt);
TREE_VEC_ELT (parmvec, i) = elt;
/* The instantiation is still a parameter pack; don't wrap it in a
NONTYPE_ARGUMENT_PACK. */
argpack = spec_parm;
spec_parm = DECL_CHAIN (spec_parm);
}
else
{
/* Fill in PARMVEC with all of the parameters. */
tree parmvec = make_tree_vec (len);
argpack = make_node (NONTYPE_ARGUMENT_PACK);
for (int i = 0; i < len; i++)
{
tree elt = spec_parm;
if (DECL_PACK_P (elt))
elt = make_pack_expansion (elt);
TREE_VEC_ELT (parmvec, i) = elt;
spec_parm = DECL_CHAIN (spec_parm);
}
/* Build the argument packs. */
SET_ARGUMENT_PACK_ARGS (argpack, parmvec);
/* Build the argument packs. */
SET_ARGUMENT_PACK_ARGS (argpack, parmvec);
}
*spec_p = spec_parm;
return argpack;
@ -25716,8 +25727,7 @@ register_parameter_specializations (tree pattern, tree inst)
}
for (; tmpl_parm; tmpl_parm = DECL_CHAIN (tmpl_parm))
{
if (!DECL_PACK_P (tmpl_parm)
|| (spec_parm && DECL_PACK_P (spec_parm)))
if (!DECL_PACK_P (tmpl_parm))
{
register_local_specialization (spec_parm, tmpl_parm);
spec_parm = DECL_CHAIN (spec_parm);

19
gcc/testsuite/g++.dg/cpp2a/lambda-generic-variadic21.C Normal file
View File

@ -0,0 +1,19 @@
// PR c++/97246
// { dg-do compile { target c++20 } }
template <int... Is, typename T>
T arg_T(decltype(Is)..., T, ...);
template <int I, int... Is>
inline constexpr auto get =
[]<typename... T>(decltype(Is)..., T... v, ...) {
static_assert( sizeof...(T) == sizeof...(v) );
if constexpr ( sizeof...(T) == 1 )
return (v,...);
else {
using V = decltype(arg_T<__integer_pack(I)...>(v...));
return get<I,__integer_pack(I)...>.template operator()<V>(v...);
}
};
static_assert( get<0>('\0', short{1}, 2, long{3}) == 0 );