Typed Template Haskell splices broken in HEAD (7.11) (#10945) · Issues · Glasgow Haskell Compiler / GHC

Typed Template Haskell splices broken in HEAD (7.11)

In the latest HEAD (e2b579e8) when I say:

$$(return [
   SigD (mkName "m")
        (ForallT [PlainTV (mkName "a")]
                 []
                 (AppT (AppT ArrowT (VarT (mkName "a"))) (VarT (mkName "a"))))
 , FunD (mkName "m")
        [Clause [VarP (mkName "x")] (NormalB (VarE (mkName "x"))) []]
 ])

I get:

ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 7.11.20151007 for x86_64-unknown-linux):
        runRnSplice
  $$(return
       [SigD
          (mkName "m")
          (ForallT
             [PlainTV (mkName "a")]
             []
             (AppT (AppT ArrowT (VarT (mkName "a"))) (VarT (mkName "a")))),
        FunD
          (mkName "m")
          [Clause [VarP (mkName "x")] (NormalB (VarE (mkName "x"))) []]])

This code compiles correctly in GHC 7.10.1.

Trac metadata

Trac field	Value
Version	7.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Template Haskell
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	goldfire
Operating system
Architecture

In the latest HEAD (e2b579e8d77357e8b36f57d15daead101586ac8e) when I say:

```hs
$$(return [
   SigD (mkName "m")
        (ForallT [PlainTV (mkName "a")]
                 []
                 (AppT (AppT ArrowT (VarT (mkName "a"))) (VarT (mkName "a"))))
 , FunD (mkName "m")
        [Clause [VarP (mkName "x")] (NormalB (VarE (mkName "x"))) []]
 ])
```

I get:

```
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 7.11.20151007 for x86_64-unknown-linux):
        runRnSplice
  $$(return
       [SigD
          (mkName "m")
          (ForallT
             [PlainTV (mkName "a")]
             []
             (AppT (AppT ArrowT (VarT (mkName "a"))) (VarT (mkName "a")))),
        FunD
          (mkName "m")
          [Clause [VarP (mkName "x")] (NormalB (VarE (mkName "x"))) []]])
```

This code compiles correctly in GHC 7.10.1.

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

| Trac field             | Value            |
| ---------------------- | ---------------- |
| Version                | 7.11             |
| Type                   | Bug              |
| TypeOfFailure          | OtherFailure     |
| Priority               | high             |
| Resolution             | Unresolved       |
| Component              | Template Haskell |
| Test case              |                  |
| Differential revisions |                  |
| BlockedBy              |                  |
| Related                |                  |
| Blocking               |                  |
| CC                     | goldfire         |
| Operating system       |                  |
| Architecture           |                  |

</details>