Plugins/dynamic loading subtly broken (it seems)

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.

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown/Multiple
Architecture