chore: reintroduce warnings as errors

package.yaml

@@ -245,8 +245,10 @@ default-extensions:
   - StandaloneKindSignatures
   - NoStarIsType
 ghc-options:
-  - -w
+  - -Wall
   - -Wmissing-home-modules
+  - -Wredundant-constraints
+  - -Widentities
   - -Wincomplete-uni-patterns
   - -fno-warn-type-defaults
   - -fno-warn-unrecognised-pragmas
@@ -256,7 +258,8 @@ ghc-options:
   - -freduction-depth=0
 when:
   - condition: flag(pedantic)
-    ghc-options:      
+    ghc-options:
+      - -Werror
       - -fwarn-tabs
   - condition: flag(dev)
     then:

src/Handler/Course/List.hs

@@ -215,7 +215,6 @@ makeCourseTable colChoices psValidator' = do
 
 getCourseListR :: Handler Html
 getCourseListR = do
-  let varNotUsed = "just a test to see whether warnings are disabled properly"
   muid <- maybeAuthId
   let colonnade = widgetColonnade $ mconcat
         [ colCourse -- colCourseDescr