[gcc r12-8310] c++, coroutines: Improve check for throwing final await [PR104051].

[Iain D Sandoe <iains@gcc.gnu.org>]

https://gcc.gnu.org/g:7b96274a340bc0e9bcaef9baff3a44ec2f12c3df

commit r12-8310-g7b96274a340bc0e9bcaef9baff3a44ec2f12c3df
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Mon Apr 18 16:23:30 2022 +0100

    c++, coroutines: Improve check for throwing final await [PR104051].
    
    We check that the final_suspend () method returns a sane type (i.e. a class
    or structure) but, unfortunately, that check has to be later than the one
    for a throwing case.  If the use returns some nonsensical type from the
    method, we need to handle that in the checking for noexcept.
    
    Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
    
            PR c++/104051
    
    gcc/cp/ChangeLog:
    
            * coroutines.cc (coro_diagnose_throwing_final_aw_expr): Handle
            non-target expression inputs.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/coroutines/pr104051.C: New test.

Diff:
---
 gcc/cp/coroutines.cc                       | 13 +++++++------
 gcc/testsuite/g++.dg/coroutines/pr104051.C | 29 +++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index 7f2377624eb..551ddc9cc41 100644
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -883,13 +883,14 @@ coro_diagnose_throwing_fn (tree fndecl)
 static bool
 coro_diagnose_throwing_final_aw_expr (tree expr)
 {
-  tree t = TARGET_EXPR_INITIAL (expr);
+  if (TREE_CODE (expr) == TARGET_EXPR)
+    expr = TARGET_EXPR_INITIAL (expr);
   tree fn = NULL_TREE;
-  if (TREE_CODE (t) == CALL_EXPR)
-    fn = CALL_EXPR_FN(t);
-  else if (TREE_CODE (t) == AGGR_INIT_EXPR)
-    fn = AGGR_INIT_EXPR_FN (t);
-  else if (TREE_CODE (t) == CONSTRUCTOR)
+  if (TREE_CODE (expr) == CALL_EXPR)
+    fn = CALL_EXPR_FN (expr);
+  else if (TREE_CODE (expr) == AGGR_INIT_EXPR)
+    fn = AGGR_INIT_EXPR_FN (expr);
+  else if (TREE_CODE (expr) == CONSTRUCTOR)
     return false;
   else
     {
diff --git a/gcc/testsuite/g++.dg/coroutines/pr104051.C b/gcc/testsuite/g++.dg/coroutines/pr104051.C
new file mode 100644
index 00000000000..ce7ae55405a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/pr104051.C
@@ -0,0 +1,29 @@
+// { dg-additional-options "-fsyntax-only" }
+#include <coroutine>
+#include <vector>
+template <typename> struct promise {
+  struct final_awaitable {
+    bool await_ready() noexcept;
+    template <typename Promise>
+    std::coroutine_handle<>
+        await_suspend(std::coroutine_handle<Promise>) noexcept;
+    void await_resume() noexcept;
+  };
+  auto get_return_object() {
+    return std::coroutine_handle<promise>::from_promise(*this);
+  }
+  auto initial_suspend() { return std::suspend_always(); }
+  auto final_suspend() noexcept { return true; }
+  void unhandled_exception();
+};
+template <typename T> struct task {
+  using promise_type = promise<T>;
+  task(std::coroutine_handle<promise<T>>);
+  bool await_ready();
+  std::coroutine_handle<> await_suspend(std::coroutine_handle<>);
+  T await_resume();
+};
+task<std::vector<int>> foo() { // { dg-error {awaitable type 'bool' is not a structure} }
+  while ((co_await foo()).empty())
+    ;
+}