Previously if someone wrote an enum containing:
- `A` (untagged)
- `B` (tagged)
- `C` (tagged)
- `D` (untagged)
- `E` (tagged)
- `F` (untagged)
serde_derive would produce errors referring to B and E only, saying
you're supposed to put untagged variants at the end. The choice of B and
E for this error doesn't make a lot of sense because in order to resolve
the issue, the user must either:
- move A and D down
or:
- move B, C, and E up.
This commit changes the error to appear on A and D instead.
a398237930