On Wed, Oct 28, 2020 at 03:18:18PM -0400, Jason Merrill via Gcc-patches wrote:
> On 10/16/20 11:31 AM, Marek Polacek wrote:
> > In this testcase we weren't able to deduce b's type:
> >
> > template<typename T> void Task() { }
> > auto b = { &Task<int> };
> >
> > because resolve_nondeduced_context doesn't iterate on the {}'s elements.
> > So make sure to look into {} too. We don't need to handle nested {}
> > here.
>
> Why don't we? That rationale should be in a comment.
I don't think we can deduce from a nested init-list; none of the following
work:
#include <initializer_list>
template<typename T>
void fn() {};
struct X { } x;
auto a = { { fn<int> } }; // unable to deduce std::initializer_list<auto>
from {{fn<int>}}
auto b = { { x, x } }; // unable to deduce std::initializer_list<auto> from
{{x, x}}
auto c = { { 1 } }; // unable to deduce std::initializer_list<auto> from {{1}}
clang++ says "cannot deduce actual type for variable 'a' with type 'auto'
from initializer list".
I've added a comment:
-- >8 --
In this testcase we weren't able to deduce b's type:
template<typename T> void Task() { }
auto b = { &Task<int> };
because resolve_nondeduced_context doesn't iterate on the {}'s elements.
So make sure to look into {} too. We don't need to handle nested {}
here.
We could either tweak resolve_nondeduced_context to handle CONSTRUCTORs
or add a _ctor version, but then resolve_nondeduced_context_or_error
would need some changes too -- it'd have to check the result of a call
to r_n_c for each element.
gcc/cp/ChangeLog:
PR c++/93107
* pt.c (do_auto_deduction): Call resolve_nondeduced_context for
the elements of a { } list.
gcc/testsuite/ChangeLog:
PR c++/93107
* g++.dg/cpp0x/initlist-deduce3.C: New test.
---
gcc/cp/pt.c | 8 ++++++-
gcc/testsuite/g++.dg/cpp0x/initlist-deduce3.C | 22 +++++++++++++++++++
2 files changed, 29 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/initlist-deduce3.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 531554d702d..b569644514c 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -29241,7 +29241,13 @@ do_auto_deduction (tree type, tree init, tree
auto_node,
if (type == error_mark_node)
return error_mark_node;
- init = resolve_nondeduced_context (init, complain);
+ if (BRACE_ENCLOSED_INITIALIZER_P (init))
+ /* We don't recurse here because we can't deduce from a nested
+ initializer_list. */
+ for (constructor_elt &elt : *CONSTRUCTOR_ELTS (init))
+ elt.value = resolve_nondeduced_context (elt.value, complain);
+ else
+ init = resolve_nondeduced_context (init, complain);
if (context == adc_decomp_type
&& auto_node == type
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist-deduce3.C
b/gcc/testsuite/g++.dg/cpp0x/initlist-deduce3.C
new file mode 100644
index 00000000000..b8417d7bf0c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist-deduce3.C
@@ -0,0 +1,22 @@
+// PR c++/93107
+// { dg-do compile { target c++11 } }
+
+using size_t = decltype(sizeof 0);
+
+namespace std {
+ template<typename T> struct initializer_list {
+ const T *ptr;
+ size_t n;
+ initializer_list(const T*, size_t);
+ };
+}
+
+template<typename T>
+void Task() {}
+
+auto a = &Task<int>;
+auto b = { &Task<int> };
+auto e{ &Task<int> };
+auto f = { &Task<int>, &Task<int> };
+std::initializer_list<void(*)()> c = { &Task<int> };
+auto d = { static_cast<void(*)()>(&Task<int>) };
base-commit: 79991e2348a864ace6ea2bf108a7502862f1129f
--
2.28.0
