Pattern match failure in RnNames.hs

When compiling dimensional-1.0.1.1 after patching numtype-dk with the patch at https://github.com/bjornbm/numtype-dk/issues/12 GHC does the "impossible":

[ 3 of 16] Compiling Numeric.Units.Dimensional.Dimensions.TypeLevel ( src/Numeric/Units/Dimensional/Dimensions/TypeLevel.hs, dist/dist-sandbox-68389a1a/build/Numeric/Units/Dimensional/Dimensions/TypeLevel.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.0.20160421 for x86_64-unknown-linux):
	Pattern match failure in do expression at compiler/rename/RnNames.hs:902:12-50

changed weight to 7

added Tbug Trac import labels

For simplicity I've provided the patched numtype-dk repo at http://code.xkrd.net/davean/numtype-dk.git

Additionally, this compiles clean on 7.10.3 (including with the patched numtype-dk).

changed the description

changed weight to 10

Here is a small reproducer:

T12026.hs:

module T12026 where

import Prelude (map ())

ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.0.20160421 for x86_64-unknown-linux):
	Pattern match failure in do expression at compiler/rename/RnNames.hs:902:12-50

Also fails with HEAD.

Trac metadata

Trac field	Value
Priority	high → highest

assigned to @mpickering

Trac metadata

Trac field	Value
Differential revisions	- → D2181

mentioned in commit 53f26f5a

changed milestone to %8.0.2

added 1 deleted label

closed

Merged to ghc-8.0 as 638c1d43.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

removed 1 deleted label

added compiler crash label

added Phighest label