c++: co_await and initializer_list [PR103871]

When flatten_await_stmt processes the backing array for an initializer_list,
we call cp_build_modify_expr to initialize the promoted variable from the
TARGET_EXPR; that needs to be accepted.

	PR c++/103871
	PR c++/98056

gcc/cp/ChangeLog:

	* typeck.cc (cp_build_modify_expr): Allow array initialization of
	DECL_ARTIFICIAL variable.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/co-await-initlist1.C: New test.

2 files changed, 23 insertions, 0 deletions

diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index d5a3e50..afb9560 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -9630,6 +9630,8 @@ cp_build_modify_expr (location_t loc, tree lhs, enum tree_code modifycode,
 	}
 
       /* Allow array assignment in compiler-generated code.  */
+      else if (DECL_P (lhs) && DECL_ARTIFICIAL (lhs))
+	/* OK, used by coroutines (co-await-initlist1.C).  */;
       else if (!current_function_decl
 	       || !DECL_DEFAULTED_FN (current_function_decl))
 	{
diff --git a/gcc/testsuite/g++.dg/coroutines/co-await-initlist1.C b/gcc/testsuite/g++.dg/coroutines/co-await-initlist1.C
new file mode 100644
index 0000000..b8e8923
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/co-await-initlist1.C
@@ -0,0 +1,21 @@
+// PR c++/103871
+// { dg-do compile { target c++20 } }
+
+#include <coroutine>
+#include <initializer_list>
+
+struct my_coro {
+  struct promise_type {
+    my_coro get_return_object();
+    std::suspend_never initial_suspend();
+    std::suspend_never final_suspend() noexcept;
+    void unhandled_exception();
+  };
+};
+
+std::suspend_never inner(std::initializer_list<int>);
+
+my_coro doesnt_work()
+{
+  co_await inner({ 1,2,3 });
+}