#dbugfix 18493

[Mike Franklin]

On Tuesday, 17 April 2018 at 12:13:06 UTC, Mike Franklin wrote:
> On Tuesday, 17 April 2018 at 05:33:53 UTC, Radu wrote:
>
>> This is very odd, as the following compiles:
>> ---
>> struct S
>> {
>>     this(this)
>>     {
>>     }
>>
>>     ~this()
>>     {
>>     }
>> }
>>
>> struct C
>> {
>>     S s1;
>> }
>> ---
>>
>> If the scope failure would cause this then I assume it would 
>> not work at all in any case.
>
> Yeah! I think that is also a bug.

Nope, that's not a bug.  The reason the try-catch is only 
generated with two or more fields is to ensure that if an 
exception is thrown while blitting `s2`, `s1`'s destructor will 
still be called.

I'm not sure what the proper fix is yet.  The compiler could 
require you to attribute `this(this)` with `nothrow` in order to 
promise the compiler that it won't throw.  Then the compiler 
would know that it wouldn't need to add the try-catch around the 
postblit because there's no way for it to throw.  That would also 
ensure consistent behavior when compiling the same code with or 
without -betterC.

However, since throwing is off-limits entirely for -betterC, it 
doesn't make much sense to generate try-catch statements, only to 
have the compiler emit an error about it.

Maybe I should implement both. I need to sleep on it.

Mike