Uncurried Parameter to n-ary Function in Type Signature Causes Crash

If you uncomment the arrow, everything's fine; GHC crashes as-is.

f :: (a -> b) {- -> -} a -> c
f = undefined

Apparently GHC incorrectly parses any n-ary function parameter followed by another uncurried parameter in type signatures.

System Info: GHC v8.2.1 GCC v5.4.0 Linux Mint (Linux 4.8.0-53-generic #56 (closed)~16.04.1-Ubuntu SMP x86_64)

ghc -v -dcore-lint:

Glasgow Haskell Compiler, Version 8.2.1, stage 2 booted by GHC version 8.0.2
Using binary package database: /usr/local/haskell/ghc-8.2.1-x86_64/lib/ghc-8.2.1/package.conf.d/package.cache
Using binary package database: /home/nic/.ghc/x86_64-linux-8.2.1/package.conf.d/package.cache
package flags []
loading package database /usr/local/haskell/ghc-8.2.1-x86_64/lib/ghc-8.2.1/package.conf.d
loading package database /home/nic/.ghc/x86_64-linux-8.2.1/package.conf.d
wired-in package ghc-prim mapped to ghc-prim-0.5.1.0
wired-in package integer-gmp mapped to integer-gmp-1.0.1.0
wired-in package base mapped to base-4.10.0.0
wired-in package rts mapped to rts
wired-in package template-haskell mapped to template-haskell-2.12.0.0
wired-in package ghc mapped to ghc-8.2.1
wired-in package dph-seq not found.
wired-in package dph-par not found.
package flags []
loading package database /usr/local/haskell/ghc-8.2.1-x86_64/lib/ghc-8.2.1/package.conf.d
loading package database /home/nic/.ghc/x86_64-linux-8.2.1/package.conf.d
wired-in package ghc-prim mapped to ghc-prim-0.5.1.0
wired-in package integer-gmp mapped to integer-gmp-1.0.1.0
wired-in package base mapped to base-4.10.0.0
wired-in package rts mapped to rts-1.0
wired-in package template-haskell mapped to template-haskell-2.12.0.0
wired-in package ghc mapped to ghc-8.2.1
wired-in package dph-seq not found.
wired-in package dph-par not found.
*** Chasing dependencies:
Chasing modules from: *bug.hs
!!! Chasing dependencies: finished in 1.14 milliseconds, allocated 0.207 megabytes
Stable obj: []
Stable BCO: []
Ready for upsweep
  [NONREC
      ModSummary {
         ms_hs_date = 2017-12-08 23:11:58.321654412 UTC
         ms_mod = Main,
         ms_textual_imps = [(Nothing, Prelude)]
         ms_srcimps = []
      }]
*** Deleting temp files:
Deleting: 
compile: input file bug.hs
*** Checking old interface for Main (use -ddump-hi-diffs for more details):
[1 of 1] Compiling Main             ( bug.hs, bug.o )
*** Parser [Main]:
!!! Parser [Main]: finished in 0.13 milliseconds, allocated 0.090 megabytes
*** Renamer/typechecker [Main]:
*** Deleting temp files:
Deleting: 
*** Deleting temp dirs:
Deleting: 
ghc: panic! (the 'impossible' happened)
  (GHC version 8.2.1 for x86_64-unknown-linux):
	repSplitAppTys
  a_anL[sk:1]
  b_anM[sk:1]
  []
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable
        pprPanic, called at compiler/types/Type.hs:808:9 in ghc:Type

Trac metadata

Trac field	Value
Version	8.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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Uncurried Parameter to n-ary Function in Type Signature Causes Crash

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