Re: [PATCH] c++, coroutines: Improve check for throwing final await [PR104051].

[Jason Merrill <jason@redhat.com>]

On 4/18/22 11:34, Iain Sandoe wrote:
> 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 user returns some nonsensical type from the
> method, we need to handle that in the checking for noexcept.
> 
> tested on x86_64-darwin, OK for mainline? (when?),

OK.

> thanks
> Iain
> 
> 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.
> ---
>   gcc/cp/coroutines.cc                       | 13 +++++-----
>   gcc/testsuite/g++.dg/coroutines/pr104051.C | 29 ++++++++++++++++++++++
>   2 files changed, 36 insertions(+), 6 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/coroutines/pr104051.C
> 
> diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
> index d2a765cac11..cb9bbed51e6 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())
> +    ;
> +}