scope(success) lowered to try-catch ?

[Steven Schveighoffer]

On 6/17/18 6:58 AM, Cauterite wrote:
> Hello,
> I'm not sure whether I'm missing something obvious here, but is there a 
> reason for scope(success) being lowered to a try-catch statement?
> I would have expected only scope(exit) and scope(failure) to actually 
> interact with exception handling, while scope(success) simply places 
> code on the path of normal control flow.
> 
> Example (windows x32):
> 
> ---
> 
> // main.d
> void main() {
>      scope(success) {}
> }
> 
>> dmd -betterC main.d
> Error: Cannot use try-catch statements with -betterC
> 
> ---
> 
> Regardless of whether -betterC is used, you can see in the disassembly 
> that having a scope(success) anywhere in the function causes the SEH 
> prologue to be emitted in the code.
> 
> Is there a reason scope(success) needs to set up for exception handling?
> Or is this a bug / potential enhancement ?

I think you are right, adding scope(success) should just add the 
statements to the end of the scope.

Here's what I think happens: Because scope(anything) needs to put things 
like this:

try
{
    normal code
    scope(success) code
} catch(Exception e) {
    scope(failure) code
    throw e;
} finally {
    scope(exit) code
}

so any time you use a scope statement, it has to set up this framework 
so it can have the correct place to put things (there may be 
scope(failure) or scope(exit) code later). But I think we can fix this.

-Steve