Fix -Wall and -Wunused-packages in stylish-haskell plugin (#4015)

* Fix -Wall and -Wunused-packages in stylish-haskell plugin

* Format

---------

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: jhrcek

plugins/hls-stylish-haskell-plugin/hls-stylish-haskell-plugin.cabal

@@ -19,14 +19,17 @@ source-repository head
     type:     git
     location: https://github.com/haskell/haskell-language-server.git
 
+common warnings
+  ghc-options: -Wall -Wunused-packages
+
 library
+  import: warnings
   exposed-modules:  Ide.Plugin.StylishHaskell
   hs-source-dirs:   src
   build-depends:
     , base             >=4.12 && <5
     , directory
     , filepath
-    , ghc
     , ghc-boot-th
     , ghcide           == 2.6.0.0
     , hls-plugin-api   == 2.6.0.0
@@ -38,6 +41,7 @@ library
   default-language: Haskell2010
 
 test-suite tests
+  import: warnings
   type:             exitcode-stdio-1.0
   default-language: Haskell2010
   hs-source-dirs:   test

plugins/hls-stylish-haskell-plugin/src/Ide/Plugin/StylishHaskell.hs

@@ -11,7 +11,8 @@ import           Control.Monad.Except             (throwError)
 import           Control.Monad.IO.Class
 import           Data.Text                        (Text)
 import qualified Data.Text                        as T
-import           Development.IDE                  hiding (pluginHandlers)
+import           Development.IDE                  hiding (getExtensions,
+                                                   pluginHandlers)
 import           Development.IDE.Core.PluginUtils
 import           Development.IDE.GHC.Compat       (ModSummary (ms_hspp_opts),
                                                    extensionFlags)