more defensive coding: guard against a non-iterable loclist

[ahrex]

Sometimes s:HandleExit can execute a deferred linter callback, which ends up setting the l:loclist that's passed into ale#engine#HandleLoclist at the end of s:HandleExit to a dictionary. This dictionary cannot be iterated over, and thus errors out.

Guard against trying to iterate over values that don't make sense.

[idbrii]

ale#engine#FixLocList doesn't do much if it receives a dictionary loclist. If it's never valid to pass a dict to it, could we prevent the error closer to where it's triggered to make it more obvious what's gone wrong? (Presumably there's a bug in some linter callback that's causing this problem?)

Instead, maybe s:HandleExit could do an :echoerr if l:linter.callback produced a dictionary and set l:loclist = []. That would make the issue more obvious to anyone writing linters and prevent further errors. Or swallow the error at that point.

[ahrex]

Updated to match this guidance:

Or swallow the error at that point.

I chose to use a try/catch with a for loop over checking the type of l:loclist because it emulates what ale#engine#FixLocList would do down the call stack, ensuring fidelity.

Thanks!

[hsanson]

Thanks.