error/warning for unary -,+ in void context?

[JeffBezanson]

I recently saw a case where code like this:

x = f(z) + g(z) - h(z)
y = ...

was reformatted to:

x = f(z) + g(z)
         - h(z)
y = ...

Of course, that silently changes the x value computed, and the value of - h(z) is just ignored. While rare, it's totally understandable how a change like this could be made accidentally. It makes me wonder if we should actually make this an error. Very few cases are affected; this can basically only happen with - and +, and it's hard to see why you would want to call those with one argument in void context.

[stevengj]

I've defined +(::String) to file an issue for the most recently loaded package, so adding a warning here would break my workflow.

[StefanKarpinski]

I realize that's not a serious comment, but that wouldn't be in void context, so this change actually wouldn't break your workflow 😁

[stevengj]

Actually it would be in a void context—the point of the joke was that this would only affect someone who has perversely defined a unwary +/- method with a side effect.

[DanielDoehring]

I recently lost half a day in debugging a statement of the form

a = b 
   + c

which is not the desired
a = b + c

I can understand that a leading - is taken without complaints, but what about throwing at least a warning if there are statements beginning with an + ?
In my opinion, there are extremely few cases (not talking about the representation of internal functions like sum for one element) where a user would use + with only one operator.