Imported from #8276 (closed), which was originally about a Haddock bug (that was different in nature but appeared similarly):

I still experience this panic on GHC 7.8.2 with Windows x86_64:

$ ghci
GHCi, version 7.8.2: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
λ> import StaticFlags
λ> import Data.IORef
λ> readIORef v_opt_C_ready
Loading package array-0.5.0.0 ... linking ... done.
Loading package deepseq-1.3.0.2 ... linking ... done.
Loading package bytestring-0.10.4.0 ... linking ... done.
Loading package containers-0.5.5.1 ... linking ... done.
Loading package Win32-2.3.0.2 ... linking ... done.
Loading package filepath-1.3.0.2 ... linking ... done.
Loading package old-locale-1.0.0.6 ... linking ... done.
Loading package time-1.4.2 ... linking ... done.
Loading package directory-1.2.1.0 ... linking ... done.
Loading package pretty-1.1.1.1 ... linking ... done.
Loading package process-1.2.0.0 ... linking ... done.
Loading package Cabal-1.18.1.3 ... linking ... done.
Loading package binary-0.7.1.0 ... linking ... done.
Loading package bin-package-db-0.0.0.0 ... linking ... done.
Loading package hoopl-3.10.0.1 ... linking ... done.
Loading package hpc-0.6.0.1 ... linking ... done.
Loading package template-haskell ... linking ... done.
Loading package transformers-0.3.0.0 ... linking ... done.
Loading package ghc-7.8.2 ... linking ... done.
False
λ> staticFlags
ghc.exe: panic! (the 'impossible' happened)
(GHC version 7.8.2 for x86_64-unknown-mingw32):
Static flags have not been initialised!
Please call GHC.parseStaticFlags early enough.

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

But not with GHC 7.8.2 on Linux x86_64:

$ ghci
GHCi, version 7.8.2: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
λ> import StaticFlags
λ> import Data.IORef
λ> readIORef v_opt_C_ready
Loading package array-0.5.0.0 ... linking ... done.
Loading package deepseq-1.3.0.2 ... linking ... done.
Loading package bytestring-0.10.4.0 ... linking ... done.
Loading package containers-0.5.5.1 ... linking ... done.
Loading package filepath-1.3.0.2 ... linking ... done.
Loading package old-locale-1.0.0.6 ... linking ... done.
Loading package time-1.4.2 ... linking ... done.
Loading package directory-1.2.1.0 ... linking ... done.
Loading package pretty-1.1.1.1 ... linking ... done.
Loading package process-1.2.0.0 ... linking ... done.
Loading package Cabal-1.18.1.3 ... linking ... done.
Loading package binary-0.7.1.0 ... linking ... done.
Loading package bin-package-db-0.0.0.0 ... linking ... done.
Loading package hoopl-3.10.0.1 ... linking ... done.
Loading package hpc-0.6.0.1 ... linking ... done.
Loading package template-haskell ... linking ... done.
Loading package transformers-0.3.0.0 ... linking ... done.
Loading package ghc-7.8.2 ... linking ... done.
True
λ> staticFlags
[]

This has caused problems for me when running programs such as HERMIT on Windows, since at some point, parseStaticFlagsFull seems to be called during program execution. A workaround is to call initStaticOpts manually somewhere in the program, but I feel like that shouldn't be necessary.

The one above was on Windows. Also reported:

Hello,

A similar panic also happens when running Liquid Haskell http://goto.ucsd.edu/~rjhala/liquid/haskell/blog/about/ on a file that uses the Units of Measure plugin https://github.com/adamgundry/uom-plugin

liquid: liquid: panic! (the 'impossible' happened)
(GHC version 7.10.1 for x86_64-unknown-linux):
Static flags have not been initialised!
Please call GHC.parseStaticFlags early enough.