df4a756c
by Matthew Pickering at 2025-06-16T09:42:19+01:00
Improve error messages when implicit lifting fails
This patch concerns programs which automatically try to fix level errors
by inserting `Lift`. For example:
```
foo x = [| x |]
~>
foo x = [| $(lift x) |]
```
Before, there were two problems with the message.
1. (#26031), the location of the error was reported as the whole
quotation.
2. (#26035), the message just mentions there is no Lift instance, but
gives no indicate why the user program needed a Lift instance in the
first place.
This problem is especially bad when you disable
`ImplicitStagePersistence`, so you just end up with a confusing "No
instance for" message rather than an error message about levels
This patch fixes both these issues.
Firstly, `PendingRnSplice` differentiates between a user-written splice
and an implicit lift. Then, the Lift instance is precisely requested
with a specific origin in the typechecker. If the instance fails to be
solved, the message is reported using the `TcRnBadlyLevelled`
constructor (like a normal level error).
Fixes #26031, #26035