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Fix multilevel deduction where an outer pack is used in the type of an

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inner non-type pack at a different index.

We previously considered the index of the outer pack (which would refer
to an unrelated template parameter) to be deduced by deducing the inner
pack, because we inspected the (largely meaningless) type of an expanded
non-type template parameter pack.
This commit is contained in:
Richard Smith 2020-06-22 16:45:12 -07:00
parent e135cf8a03
commit 009c9b83ac
2 changed files with 7 additions and 6 deletions
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5
clang/lib/Sema/SemaTemplateDeduction.cpp
View File

@ -738,8 +738,9 @@ private:
// type, so we need to collect the pending deduced values for those packs.
if (auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(
TemplateParams->getParam(Index))) {
if (auto *Expansion = dyn_cast<PackExpansionType>(NTTP->getType()))
ExtraDeductions.push_back(Expansion->getPattern());
if (!NTTP->isExpandedParameterPack())
if (auto *Expansion = dyn_cast<PackExpansionType>(NTTP->getType()))
ExtraDeductions.push_back(Expansion->getPattern());
}
// FIXME: Also collect the unexpanded packs in any type and template
// parameter packs that are pack expansions.

8
clang/test/SemaTemplate/deduction-guide.cpp
View File

@ -1,14 +1,14 @@
// RUN: %clang_cc1 -std=c++2a -verify -ast-dump -ast-dump-decl-types -ast-dump-filter "deduction guide" %s | FileCheck %s
// expected-no-diagnostics
template<auto ...> struct X {};
template<typename T, typename ...Ts> struct A { // expected-note 2{{candidate}}
template<Ts ...Ns, T *...Ps> A(X<Ps...>, Ts (*...qs)[Ns]); // expected-note {{candidate}}
template<typename T, typename ...Ts> struct A {
template<Ts ...Ns, T *...Ps> A(X<Ps...>, Ts (*...qs)[Ns]);
};
int arr1[3], arr2[3];
short arr3[4];
// FIXME: The CTAD deduction here succeeds, but the initialization deduction spuriously fails.
A a(X<&arr1, &arr2>{}, &arr1, &arr2, &arr3); // FIXME: expected-error {{no matching constructor}}
A a(X<&arr1, &arr2>{}, &arr1, &arr2, &arr3);
using AT = decltype(a);
using AT = A<int[3], int, int, short>;