HEAD panic: tcSyntaxOp "noSyntaxExpr"
The following program triggers a bug in 8.2.2 and 8.5.20171215.
```hs
-- Checks that the ordering constraint on the groupWith function is respected
{-# OPTIONS_GHC -XMonadComprehensions -XTransformListComp #-}
module ShouldFail where
import GHC.Exts (groupWith)
data Unorderable = Gnorf | Pinky | Brain
foo = [ ()
| Gnorf <- [Gnorf, Brain]
, then group by x using groupWith
]
```
Reproduce:
```
ghc bug.hs
```
Output:
`
[1 of 1] Compiling ShouldFail ( bug.hs, bug.o )
ghc: panic! (the 'impossible' happened)
(GHC version 8.5.20171215 for x86_64-unknown-linux):
tcSyntaxOp
"noSyntaxExpr"
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable
pprPanic, called at compiler/typecheck/TcExpr.hs:1436:31 in ghc:TcExpr
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug`
<details><summary>Trac metadata</summary>
| Trac field | Value |
| ---------------------- | ------------ |
| Version | 8.2.2 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture | |
</details>
<!-- {"blocked_by":[],"summary":"HEAD panic: tcSyntaxOp \"noSyntaxExpr\"","status":"New","operating_system":"","component":"Compiler","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"8.2.2","keywords":[],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"Bug","description":"\r\nThe following program triggers a bug in 8.2.2 and 8.5.20171215. \r\n\r\n{{{#!hs\r\n-- Checks that the ordering constraint on the groupWith function is respected\r\n{-# OPTIONS_GHC -XMonadComprehensions -XTransformListComp #-}\r\nmodule ShouldFail where\r\nimport GHC.Exts (groupWith)\r\ndata Unorderable = Gnorf | Pinky | Brain\r\nfoo = [ ()\r\n | Gnorf <- [Gnorf, Brain]\r\n , then group by x using groupWith\r\n ]\r\n}}}\r\n\r\nReproduce:\r\n\r\n{{{\r\nghc bug.hs\r\n}}}\r\n\r\nOutput:\r\n{{{\r\n[1 of 1] Compiling ShouldFail ( bug.hs, bug.o )\r\nghc: panic! (the 'impossible' happened)\r\n (GHC version 8.5.20171215 for x86_64-unknown-linux):\r\n\ttcSyntaxOp\r\n \"noSyntaxExpr\"\r\n Call stack:\r\n CallStack (from HasCallStack):\r\n callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable\r\n pprPanic, called at compiler/typecheck/TcExpr.hs:1436:31 in ghc:TcExpr\r\n\r\nPlease report this as a GHC bug: http://www.haskell.org/ghc/reportabug}}}","type_of_failure":"OtherFailure","blocking":[]} -->
issue