DND_Reborn
The High Aldwin
But that's about seeing, not about having a path to the target. You can Bless an invisible ally as long as they're not behind total cover.
So, basically, their logic is magical energies can't penetrate barriers? I suppose I could buy that in certain situations (such as behind a wall, with no ready access within range), but it seems ludicrous for examples when someone is behind a glass window.
But even when an open path exists but is not a straight line (such as in the OP example)? Nah, I can't go with that one--even if others say it is a house-rule, I say just a difference in interpretation. After all, the text does not say a "straight" clear path.

Oh, sorry, I misread. So this is about range, and whether you can choose new targets if you initially pick one that turns out not to be valid. I don't see what it has to do with total cover?
No, it was an example of how being seen should be the real prerequisite to target pretty much anything other than AoE spells/effects. Total cover should prevent things from being seen, which would make the OP's situation obvious: you can't see your ally around the corner, you can't target him with Bless.
I am not thrilled about that either, TBH. I think the wording in Bless should say "chosen creature" instead of "target" to avoid confusion.