normaliseType is not well-kinded (#14729) · Issues · Glasgow Haskell Compiler / GHC

normaliseType is not well-kinded

Suppose we have

Proxy :: forall k. k -> Type

type family F a
type instance F Int = Bool

and we're trying to normalise the target

Proxy (F Int) x

Clearly, for this target to be well kinded, we need x :: F Int. Currently, the output of normaliseType is Proxy Bool x, which is just plain wrong.

I need to implement logic like in flatten_args on my branch in normaliseType to fix this.

Trac metadata

Trac field	Value
Version	8.2.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

Suppose we have

```
Proxy :: forall k. k -> Type

type family F a
type instance F Int = Bool
```

and we're trying to normalise the target

```
Proxy (F Int) x
```

Clearly, for this target to be well kinded, we need `x :: F Int`. Currently, the output of `normaliseType` is `Proxy Bool x`, which is just plain wrong.

I need to implement logic like in `flatten_args` on [my branch](https://github.com/goldfirere/ghc) in `normaliseType` to fix this.

<details><summary>Trac metadata</summary>

| Trac field             | Value        |
| ---------------------- | ------------ |
| Version                | 8.2.2        |
| Type                   | Bug          |
| TypeOfFailure          | OtherFailure |
| Priority               | normal       |
| Resolution             | Unresolved   |
| Component              | Compiler     |
| Test case              |              |
| Differential revisions |              |
| BlockedBy              |              |
| Related                |              |
| Blocking               |              |
| CC                     |              |
| Operating system       |              |
| Architecture           |              |

</details>