Unicode reports with no messages are not very obvious

[ISSOtm]

Those print

Error: can't compare apples with oranges
   ╭─[ <unknown>:1:1 ]
   │
 1 │ apple == orange;
   │ ─────    ──────
───╯

...which I find visually unclear without the tip pointing to the label.

Suggestion: print tildes (~) for labels that lack such a tip?

[zesterer]

Hmm, I'm struggling to imagine how this could be improved. If desired, a message can just be added to the label: but since this has not been done, I'd think that this diagnostic is rendering as it should. When you say 'print tildes', what do you mean? I don't think that ~~~~~ is any more readable than a horizontal bar, personally.

[ISSOtm]

I think it's not necessarily more readable, but it's more eye-catching. Straight bars look merely like underlines, and IMO don't do a very good job at pointing out the relevant sections of the snippet (at least without colour).

[zesterer]

I've just been playing around with it, but I don't think that either tildes or 'horizontal spans' look like they're in the right place.

Straight bars look merely like underlines

Well, that's perfect: it is an underline.

[ISSOtm]

Yeah, but I find that my eye skips over straight lines too easily. Maybe that's just a me problem. (And, again, colour helps, but sometimes that's disabled.)

There is precedent in using tildes in at least Clang and I think GCC? Though I don't know if they had a design rationale for that.

[zesterer]

Hmm. While I do understand what you're saying, I think that switching to an entirely different style of formatting for specific labels like this is likely to be confusing to users (it implies that the differing style means something). If there's a way to reconcile these two things, I'd be interested to hear about it. For now, I'm going to put this issue on the back burner.

[ISSOtm]

Fair analysis, yeah. (Perhaps a “opinions wanted” label would work better, since it's not quite technical help that's wanted?)

[moritzruth]

I really like the look of the "horizontal span"-style marker:

If this could be could used for all spans, even for spans with labels, you would not have the problem of users thinking it means something special.

I think the tildes look worse than the lines we have now without providing any benefit.