PatternSynonyms/OverloadedStrings regression in GHC HEAD

purescript-0.10.7 fails to build with GHC HEAD at the moment due to an apparent regression in the way pattern synonyms and overloaded strings interact. Here is a simplified example:

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE PatternSynonyms #-}
module Bug where

import Data.ByteString

newtype ProperName =
  ProperName { runProperName :: ByteString
               -- purescript actually uses the Text type, but this works
               -- just as well for the purposes of illustrating the bug
             }
newtype ModuleName = ModuleName [ProperName]

pattern TypeDataSymbol :: ModuleName
pattern TypeDataSymbol = ModuleName [ProperName "Type",ProperName "Data", ProperName "Symbol"]

Compiling this with GHC 7.10.3 or 8.0.2 works without issue. In GHC HEAD, if you compile this with optimization enabled, it'll trigger a GHC panic:

$ ~/Software/ghc5/inplace/bin/ghc-stage2 -O1 -fforce-recomp Bug.hs                                                                     
[1 of 1] Compiling Bug              ( Bug.hs, Bug.o )                                     
ghc-stage2: panic! (the 'impossible' happened)                                            
  (GHC version 8.1.20170303 for x86_64-unknown-linux):                                    
        isUnliftedType                                                                    
  r_a28T :: TYPE rep_a28S                                                                 
  Call stack:                                                                             
      CallStack (from HasCallStack):                                                      
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1191:58 in ghc:Outputable                                                                                    
        callStackDoc, called at compiler/utils/Outputable.hs:1195:37 in ghc:Outputable    
        pprPanic, called at compiler/types/Type.hs:1961:10 in ghc:Type

The presence of optimization is crucial for reproducing this bug, as compiling it with -O0 does not trigger the panic.

Trac metadata

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

changed milestone to %8.2.1

changed weight to 10

added Tbug Trac import labels

Aha. Thanks. Easy fix validating now.

mentioned in commit 8e053700

closed

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Test case	- → polykinds/T13394

reopened

Thanks, Simon. But you didn't include the original program as the test case! Rather, you included a slightly tweaked program that doesn't have as many list elements in TypeDataSymbol. This is crucial, as the original program still fails with a GHC panic even after 8e053700:

$ ~/Software/ghc2/inplace/bin/ghc-stage2 -O1 -fforce-recomp Bug.hs
[1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.1.20170307 for x86_64-unknown-linux):
        runtimeRepPrimRep
  typePrimRep (r_a28P :: TYPE rep_a28O)
  rep_a28O
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1191:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1195:37 in ghc:Outputable
        pprPanic, called at compiler/simplStg/RepType.hs:360:5 in ghc:RepType

Trac metadata

Trac field	Value
Resolution	ResolvedFixed → Unresolved

mentioned in commit bc0f3abd

closed

OK, now it should be fixed. There was a second bug!

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Test case	polykinds/T13394 → polykinds/T13394, T13394a

mentioned in issue #14393 (closed)

changed milestone to %8.2.2

I've merged #13394 (closed) to ghc-8.2 with 704cbae2. This will be present in 8.2.2.

added PatternSynonyms label

added compiler crash label

mentioned in issue #16509 (closed)

added Phighest label