Re: [PATCH] coroutines : Do not accept throwing final await expressions [PR95616].

[Nathan Sidwell <nathan@acm.org>]

On 3/4/21 2:54 PM, Iain Sandoe wrote:
> Hi,
> 
>  From the PR:
> 
> The wording of [dcl.fct.def.coroutine]/15 states:
>   * The expression co_await promise.final_suspend() shall not be
>     potentially-throwing ([except.spec]).
> 
> See http://eel.is/c++draft/dcl.fct.def.coroutine#15
> and http://eel.is/c++draft/except.spec#6
> 
> ie. all of the following must be declared noexcept (if they form part of the await-expression):
> - promise_type::final_suspend()
> - finalSuspendObj.operator co_await()
> - finalSuspendAwaiter.await_ready()
> - finalSuspendAwaiter.await_suspend()
> - finalSuspendAwaiter.await_resume()
> - finalSuspedObj destructor
> - finalSuspendAwaiter destructor
> 
> This implements the checks for these cases and rejects such code with
> a diagnostic.
> 
> [ accepts invalid ]
> tested on x86_64-darwin, x86_64-linux-gnu,
> OK for master / 10.x?
> thanks
> Iain
> 
> 
> gcc/cp/ChangeLog:
> 
> 	PR c++/95616
> 	* coroutines.cc (coro_diagnose_throwing_fn): New helper.
> 	(coro_diagnose_throwing_final_aw_expr): New helper.
> 	(build_co_await): Diagnose throwing final await expression
> 	components.
> 	(build_init_or_final_await): Diagnose a throwing promise
> 	final_suspend() call.
> 

ok.  Does this DTRT in the presence of -fno-exceptions?  (i.e. use of 
that flag means you don't have to decorate everything with noexcept)

nathan

-- 
Nathan Sidwell