Replace @assert with throw() in winprompt()

[petershintech]

1. The extra argument, stdcall, is a bug. The return value is just a boolean.
2. T conversion can be failed if something wrong happens in the system. So, in this case, need to raise an exception rather than assertion. I think SystemError would be the best choice for this case.

Wondering why the extra argument bug was not caught by tests. If it is missing in tests, can I have your help to add a unit test for winprompt()?

[yuyichao]

https://docs.julialang.org/en/v1/manual/calling-c-and-fortran-code/#Calling-Convention-1

[yuyichao]

stdcall has nothing to do with return type.

[petershintech]

Yichao. Thanks for the information. I only checked https://docs.julialang.org/en/v1/base/c/#ccall
It seems the doc string of ccall() needs to be updated. Am I right?

.

[JeffBezanson]

According to its documentation, this function can only fail if the buffer is too small. Do we have a reason to believe 1024 is always enough? If so, then the existing assertion is actually correct. (Either way though, if this happens it's our bug, since there's nothing the user/caller can do to get a bigger buffer.)

[JeffBezanson]

Also, when the function fails it updates the length argument to tell you how much space is needed. So an alternative fix is to handle that case and retry the call with a bigger buffer, after which an assertion would be warranted.

[petershintech]

I think retrying the call with a bigger buffer is a good choice to make the code more solid, but if it fails again, we need to raise an exception rather than insert an assertion, because the outcome of the call depends on the response of an external program. If Julia allows @Assert to be deactivated in the future, the critical check can be bypassed.

[musm]

#38828 addresses resizing the buffer in case of failure