[SWF] Safe cast doesn't throw exception in case of a failing cast

[wolfhoundgelert]

In the haxe manual https://haxe.org/manual/expression-cast-safe.html

The Haxe compiler guarantees that an exception of type String is thrown in this case.

But nothing happens on SWF-target https://try.haxe.org/#9c38D

[Simn]

Are you testing this in a debug flash player? Check if a throw does something I guess.

[wolfhoundgelert]

[back2dos]

You're not using the result of the cast, so it's just optimized away:

• result unused, no exception: https://try.haxe.org/#eCeBc
• result used, exception: https://try.haxe.org/#1914E

Related: #5774

[nadako]

#5774 was about unsafe cast, this is a safe cast tho, so it shouldn't be optimized away, I think.

[Simn]

You're not using the result of the cast, so it's just optimized away

That shouldn't be the case because a safe-cast is not side-effect free. I see the cast in the dump...

[nadako]

This condition looks suspicious https://github.com/HaxeFoundation/haxe/blob/development/src/generators/genswf9.ml#L1318, but i'm pretty sure it was there for ages...

[wolfhoundgelert]

@back2dos

result used, exception: https://try.haxe.org/#1914E

Ok, but we have different behavior on JS (exception) and on SWF (null) if we do cast with null
https://try.haxe.org/#fAaDd

minimal: https://try.haxe.org/#A384c

[Simn]

This is indeed a (very old) SWF generator bug.

[wolfhoundgelert]

@nadako

but i'm pretty sure it was there for ages...

I've caught this bug on some big real project due to huge amount of error-reports in our log-system))

[wolfhoundgelert]

Thanks a lot!)