Plugin recompilation check still panics

I get a panic as follows when trying to use a plugin with the latest commit on the 8.6 branch.

<no location info>: error:
    ghc: panic! (the 'impossible' happened)
  (GHC version 8.6.1.20180803 for x86_64-unknown-linux):
	mkPluginUsage: file not found
  LiftPlugin /nix/store/q8rg4mca5zqv98arpxd7164pqa72hf1n-ncurses-6.1/lib/libHSlift-plugin-0.1.0.0-LpWZumtLigSEjndVxGCyUH-ghc8.6.1.20180803.so
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1164:37 in ghc:Outputable
        pprPanic, called at compiler/deSugar/DsUsage.hs:215:15 in ghc:DsUsage

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

My example is nixified and not very minimal but I can provide it tomorrow if that would help.

Trac metadata

Trac field	Value
Version	8.4.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	highest
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed milestone to %8.6.1

changed weight to 10

added Tbug Trac import labels

Repro:

git clone -b plugin https://github.com/LightAndLight/typed-cfg.git
cachix use mpickering
nix-shell
cabal build

Trac metadata

Trac field	Value
Differential revisions	- → D5048

mentioned in commit b324c562

added 1 deleted label

closed

Merged with 13105a1a.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

removed 1 deleted label

mentioned in issue #15564 (closed)

added Phighest label