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c++: Diagnose references to void in structured bindings [PR99650]

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We ICE on the following testcase, because std::tuple_element<...,...>::type
is void and for structured bindings we therefore need to create
void & or void && which is invalid.  We created such REFERENCE_TYPE and
later ICEd in the middle-end.
The following patch fixes it by diagnosing that.

2021-03-23  Jakub Jelinek  <jakub@redhat.com>

	PR c++/99650
	* decl.c (cp_finish_decomp): Diagnose void initializers when
	using tuple_element and get.

	* g++.dg/cpp1z/decomp55.C: New test.
This commit is contained in:
Jakub Jelinek 2021-03-23 10:23:42 +01:00
parent a28cc94a27
commit 3e07e7a6a7
2 changed files with 25 additions and 0 deletions
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6
gcc/cp/decl.c
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@ -8629,6 +8629,12 @@ cp_finish_decomp (tree decl, tree first, unsigned int count)
: get_tuple_element_type (type, i));
input_location = sloc;
if (VOID_TYPE_P (eltype))
{
error ("%<std::tuple_element<%u, %T>::type%> is %<void%>",
i, type);
eltype = error_mark_node;
}
if (init == error_mark_node || eltype == error_mark_node)
{
inform (dloc, "in initialization of structured binding "

19
gcc/testsuite/g++.dg/cpp1z/decomp55.C Normal file
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@ -0,0 +1,19 @@
// PR c++/99650
// { dg-do compile { target c++17 } }
namespace std {
template<typename T> struct tuple_size;
template<int, typename> struct tuple_element;
}
struct A {
int i;
template <int I> void get() { }
};
template<> struct std::tuple_size<A> { static const int value = 2; };
template<int I> struct std::tuple_element<I,A> { using type = void; };
A a = { 42 };
auto [ x, y ] = a; // { dg-error ".std::tuple_element<0, A>::type. is .void." }
// { dg-message "in initialization of structured binding variable 'x'" "" { target *-*-* } .-1 }