I'm a little confused as to the intent of this message. Is it trying to just point at the += (which seems correct)? If so, the underline-like arrow beneath the rest of the line looks really odd to me. Might just not be used to it though.. nor do I have any ideas as to what else we could do.

@Mark-Simulacrum, the primary span which doesn't have a label is as follows:

15 |     map.entry("e").or_insert(0) += 1;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

My assumption is that there should be only one span in this error, either:

15 |     map.entry("e").or_insert(0) += 1;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot use `+=` on type `&mut {integer}`

or

15 |     map.entry("e").or_insert(0) += 1;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot use `+=` on type `&mut {integer}`

Once we fix that, I'll have to find a new way to have a test for this bug, though.

Oh. I would have expected the span to be on +=, actually, not the whole expression or some part of it. Obviously that's a separate discussion though -- no need to fix here.

it's progress for sure. I still find these sorts of overlap scenarios pretty mind boggling regardless, though i'm not sure how best to fix in general. I'd sort of like to separate the ^^^ and --- on different lines. i.e., if I was highlighting this by hand I would probably do:

a  bc  d
^^^^
    ----

but anyway.