Renamer is not applied properly to the expressions in declaration splices

To recreate this make a Haskell file say named 'T.hs', with the following code:

{-# LANGUAGE TemplateHaskell #-}
(() -> ())

Then try to compile it:

$> ghc-stage2 T.hs
[...]
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.1.20160617 for x86_64-unknown-linux):
	tcMonoExpr _
[...]

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

mentioned in issue #11184 (closed)

mentioned in issue #12411 (closed)

changed weight to 5

added Tbug Trac import labels

similarly for

{-# LANGUAGE TemplateHaskell #-}
a@b

added newcomer label

changed title from Bug (or Unhelpful Error) with TemplateHaskell to Renamer is not applied properly to the expressions in declaration splices

changed weight to 7

Trac metadata

Trac field	Value
Priority	normal → high

The problem here is that RnExpr.patSynErr returns a EWildPat, which shouldn't appear in the AST post-renaming. See D2539 for one possible fix.

Trac metadata

Trac field	Value
Differential revisions	- → D2539

changed milestone to %8.0.2

Trac metadata

Trac field	Value
Version	8.1 → 8.0.1

I've updated D2539 with a new approach suggested by Simon. Let's see whether it passes Harbormaster.

BTW, #12411 (closed) demonstrates another occurrence of the same error message. I have no idea if Phab:2539 happens to fix that bug too, however.

mentioned in commit bce99086

closed

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

mentioned in commit 184d7cb8

Ben, you set this milestone to 8.0.2, but marked the issue as closed. Should this be set as merge?

Thanks for pointing that out, Ryan! #12584 (closed) was merged to ghc-8.0 as 47ae01bf.

mentioned in issue #12788 (closed)

mentioned in commit ec22bacd

added Phigh label