On 3/16/22 17:18, Marek Polacek wrote:
Zero-length pack expansions are treated as if no list were provided
at all, that is, with
template<typename...> struct S { };
template<typename T, typename... Ts>
void g() {
S<std::is_same<T, Ts>...>;
}
g<int> will result in S<>. In the following test we have something
similar:
template <typename T, typename... Ts>
using IsOneOf = disjunction<is_same<T, Ts>...>;
and then we have "IsOneOf<OtherHolders>..." where OtherHolders is an
empty pack. Since r11-7931, we strip_typedefs in TYPE_PACK_EXPANSION.
In this test that results in "IsOneOf<OtherHolders>" being turned into
"disjunction<>". So the whole expansion is now "disjunction<>...". But
then we error in make_pack_expansion because find_parameter_packs_r won't
find the pack OtherHolders.
We strip the alias template because dependent_alias_template_spec_p says
it's not dependent. It it not dependent because this alias is not
TEMPLATE_DECL_COMPLEX_ALIAS_P. My understanding is that currently we
consider an alias complex if it
1) expands a pack from the enclosing class, as in
template<template<typename... U> typename... TT>
struct S {
template<typename... Args>
using X = P<TT<Args...>...>;
};
where the alias expands TT; or
2) the expansion does *not* name all the template parameters, as in
template<typename...> struct R;
template<typename T, typename... Ts>
using U = R<X<Ts>...>;
where T is not named in the expansion.
But IsOneOf is neither. And it can't know how it's going to be used.
Therefore I think we cannot make it complex (and in turn dependent) to fix
this bug.
After much gnashing of teeth, I think we simply want to avoid stripping
the alias if the new pattern doesn't have any parameter packs to expand.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/11?
PR c++/104008
gcc/cp/ChangeLog:
* tree.cc (strip_typedefs): Don't strip an alias template when
doing so would result in losing a parameter pack.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/variadic-alias3.C: New test.
* g++.dg/cpp0x/variadic-alias4.C: New test.
---
gcc/cp/tree.cc | 13 +++++-
gcc/testsuite/g++.dg/cpp0x/variadic-alias3.C | 45 ++++++++++++++++++
gcc/testsuite/g++.dg/cpp0x/variadic-alias4.C | 48 ++++++++++++++++++++
3 files changed, 105 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/variadic-alias3.C
create mode 100644 gcc/testsuite/g++.dg/cpp0x/variadic-alias4.C
diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 6e9be713c51..eb59e56610b 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -1778,7 +1778,18 @@ strip_typedefs (tree t, bool *remove_attributes,
unsigned int flags)
if (TYPE_P (pat))
{
type = strip_typedefs (pat, remove_attributes, flags);
- if (type != pat)
+ /* Empty packs can thwart our efforts here. Consider
+
+ template <typename T, typename... Ts>
+ using IsOneOf = disjunction<is_same<T, Ts>...>;
+
+ where IsOneOf seemingly uses all of its template parameters in
+ its expansion (and does not expand a pack from the enclosing
+ class), so the alias is not marked as complex. However, it may
+ be used as in "IsOneOf<Ts>", where Ts is an empty parameter pack,
+ and stripping it down into "disjunction<>" here would exclude the
+ Ts pack, resulting in an error. */
+ if (type != pat && uses_parameter_packs (type))
I wonder if we want to verify that the result of uses_parameter_packs
matches PACK_EXPANSION_PARAMETER_PACKS, not just that it's non-null?
But I can't think how to write a testcase where those two questions have
different answers.
The patch is OK, thanks.
{
result = copy_node (t);
PACK_EXPANSION_PATTERN (result) = type;
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic-alias3.C
b/gcc/testsuite/g++.dg/cpp0x/variadic-alias3.C
new file mode 100644
index 00000000000..6b6dd9f4c85
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic-alias3.C
@@ -0,0 +1,45 @@
+// PR c++/104008
+// { dg-do compile { target c++11 } }
+
+template <typename...> struct conjunction;
+template <typename...> struct disjunction;
+template <typename, typename> struct is_same;
+template <bool> struct enable_if;
+template <bool _Cond> using enable_if_t = typename enable_if<_Cond>::type;
+struct B;
+struct __uniq_ptr_impl {
+ struct _Ptr {
+ using type = B *;
+ };
+ using pointer = _Ptr::type;
+};
+struct unique_ptr {
+ using pointer = __uniq_ptr_impl::pointer;
+ unique_ptr(pointer);
+};
+template <typename T, typename... Ts>
+using IsOneOf = disjunction<is_same<T, Ts>...>;
+
+template <typename...> struct any_badge;
+
+struct badge {
+ badge(any_badge<>);
+ badge();
+};
+
+template <typename...> struct any_badge {
+ template <typename... OtherHolders,
+ enable_if_t<conjunction<IsOneOf<OtherHolders>...>::value>>
+ any_badge();
+};
+
+template <typename, typename... _Args> unique_ptr make_unique(_Args... __args);
+
+struct B {
+ B(badge);
+ unique_ptr b_ = make_unique<B>(badge{});
+};
+
+template <typename, typename... _Args> unique_ptr make_unique(_Args... __args)
{
+ return new B(__args...);
+}
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic-alias4.C
b/gcc/testsuite/g++.dg/cpp0x/variadic-alias4.C
new file mode 100644
index 00000000000..896a4725627
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic-alias4.C
@@ -0,0 +1,48 @@
+// PR c++/104008
+// { dg-do compile { target c++11 } }
+// Differs from variadic-alias3.C only in the pattern of a pack expansion
+// in line 34. But it's important to check that we also deal with more
+// complex patterns.
+
+template <typename...> struct conjunction;
+template <typename...> struct disjunction;
+template <typename, typename> struct is_same;
+template <bool> struct enable_if;
+template <bool _Cond> using enable_if_t = typename enable_if<_Cond>::type;
+struct B;
+struct __uniq_ptr_impl {
+ struct _Ptr {
+ using type = B *;
+ };
+ using pointer = _Ptr::type;
+};
+struct unique_ptr {
+ using pointer = __uniq_ptr_impl::pointer;
+ unique_ptr(pointer);
+};
+template <typename T, typename... Ts>
+using IsOneOf = disjunction<is_same<T, Ts>...>;
+
+template <typename...> struct any_badge;
+
+struct badge {
+ badge(any_badge<>);
+ badge();
+};
+
+template <typename...> struct any_badge {
+ template <typename... OtherHolders,
+ enable_if_t<conjunction<IsOneOf<OtherHolders>&...>::value>>
+ any_badge();
+};
+
+template <typename, typename... _Args> unique_ptr make_unique(_Args... __args);
+
+struct B {
+ B(badge);
+ unique_ptr b_ = make_unique<B>(badge{});
+};
+
+template <typename, typename... _Args> unique_ptr make_unique(_Args... __args)
{
+ return new B(__args...);
+}
base-commit: 7fd6e36ea9aa8575841ff1da08b4aebc0298abe2
