From 6fb7e3c29188ab7cde0b963957caf6182536c77d Mon Sep 17 00:00:00 2001
From: Marek Polacek <polacek@redhat.com>
Date: Fri, 16 Oct 2020 11:00:12 -0400
Subject: [PATCH] c++: Deducing type from initializer_list<auto> [PR93107]

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>) };
-- 
2.30.2