Add flag for turning warnings into errors

.github/workflows/ci.yaml

@@ -25,7 +25,7 @@ jobs:
         with:
           ghc-version: ${{ matrix.ghc }}
           cabal-version: ${{ matrix.cabal }}
-      - run: cabal configure --enable-tests
+      - run: cabal configure --enable-tests --flags pedantic --jobs
       - run: cabal freeze
       - run: cat cabal.project.freeze
       - uses: actions/cache@v2

brittany.cabal

@@ -30,6 +30,11 @@ source-repository head
   type: git
   location: https://github.com/lspitzner/brittany.git
 
+flag pedantic
+  default: False
+  description: Enables @-Werror@, which turns warnings into errors.
+  manual: True
+
 common library
   build-depends:
     , aeson ^>= 2.0.1
@@ -75,6 +80,9 @@ common library
     -Wno-safe
     -Wno-unsafe
 
+  if flag(pedantic)
+    ghc-options: -Werror
+
 common executable
   import: library