Generate a diff between two sets of options.

haskell-ci.cabal

@@ -81,6 +81,7 @@ library haskell-ci-internal
     HaskellCI.Config.CopyFields
     HaskellCI.Config.Docspec
     HaskellCI.Config.Doctest
+    HaskellCI.Config.Diff
     HaskellCI.Config.Dump
     HaskellCI.Config.Empty
     HaskellCI.Config.Folds

src/HaskellCI/Config/Diff.hs

@@ -0,0 +1,131 @@
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FunctionalDependencies #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TypeApplications  #-}
+module HaskellCI.Config.Diff where
+
+import HaskellCI.Prelude
+
+import Distribution.Simple.Utils (fromUTF8BS)
+import Distribution.Fields.Field (FieldName)
+import Distribution.Utils.ShortText (fromShortText)
+
+import qualified Distribution.Compat.Lens        as L
+import qualified Distribution.Compat.CharParsing as C
+import qualified Distribution.FieldGrammar       as C
+import qualified Distribution.Parsec             as C
+import qualified Distribution.Pretty             as C
+import qualified Text.PrettyPrint                as PP
+
+import HaskellCI.OptionsGrammar
+
+data ShowDiffOptions = ShowAllOptions | ShowChangedOptions
+    deriving (Eq, Show, Generic, Binary)
+
+instance C.Parsec ShowDiffOptions where
+    parsec = ShowAllOptions <$ C.string "all"
+        <|> ShowChangedOptions <$ C.string "changed"
+
+instance C.Pretty ShowDiffOptions where
+    pretty ShowAllOptions = PP.text "all"
+    pretty ShowChangedOptions = PP.text "changed"
+
+data DiffConfig = DiffConfig
+    { diffShowOptions :: ShowDiffOptions
+    , diffShowOld :: Bool
+    } deriving (Show, Generic, Binary)
+
+diffConfigGrammar
+    :: ( OptionsGrammar c g
+       , Applicative (g DiffConfig)
+       , c (Identity ShowDiffOptions))
+    => g DiffConfig DiffConfig
+diffConfigGrammar = DiffConfig
+    <$> C.optionalFieldDef "diff-show-options" (field @"diffShowOptions") ShowChangedOptions
+        ^^^ help "Which fields to show"
+    <*> C.booleanFieldDef "diff-show-old" (field @"diffShowOld") False
+        ^^^ help "Show the old values for every field"
+
+newtype DiffOptions s a =
+  DiffOptions { runDiffOptions :: (s, s) -> DiffConfig -> [String] }
+  deriving Functor
+
+instance Applicative (DiffOptions s) where
+    pure _ = DiffOptions $ \_ _ -> []
+    DiffOptions f <*> DiffOptions x = DiffOptions (f <> x)
+
+diffConfigs :: DiffConfig -> DiffOptions a a -> a -> a -> [String]
+diffConfigs config grammar oldVal newVal =
+  runDiffOptions grammar (oldVal, newVal) config
+
+diffUnique
+    :: Eq b
+    => (a -> b)
+    -> (a -> String)
+    -> FieldName
+    -> L.ALens' s a
+    -> (s, s)
+    -> DiffConfig
+    -> [String]
+diffUnique project render fn lens (diffOld, diffNew) opts =
+  case diffShowOptions opts of
+    ShowChangedOptions | notEqual -> []
+    ShowAllOptions | notEqual -> newLine
+    _ -> oldLine ++ newLine
+  where
+    notEqual = project oldValue == project newValue
+    oldValue = L.aview lens $ diffOld
+    newValue = L.aview lens $ diffNew
+
+    oldLine
+        | diffShowOld opts = ["-- " ++ fromUTF8BS fn ++ ": " ++ render oldValue]
+        | otherwise = []
+
+    newLine = [ fromUTF8BS fn ++ ": " ++ render newValue, ""]
+
+
+instance C.FieldGrammar C.Pretty DiffOptions where
+    blurFieldGrammar lens (DiffOptions diff) =
+        DiffOptions $ diff . bimap (L.aview lens) (L.aview lens)
+
+    uniqueFieldAla fn pack valueLens = DiffOptions $
+        diffUnique (C.prettyShow . pack) (C.prettyShow . pack) fn valueLens
+
+    booleanFieldDef fn valueLens _ = DiffOptions $
+        diffUnique id C.prettyShow fn valueLens
+
+    optionalFieldAla fn pack valueLens = DiffOptions $
+        diffUnique toPretty toPretty fn valueLens
+      where
+        toPretty = maybe "" C.prettyShow . fmap pack
+
+    optionalFieldDefAla fn pack valueLens _ = DiffOptions $
+        diffUnique id (C.prettyShow . pack) fn valueLens
+
+    monoidalFieldAla fn pack valueLens = DiffOptions $
+        diffUnique (C.prettyShow . pack) (C.prettyShow . pack) fn valueLens
+
+    freeTextField fn valueLens = DiffOptions $
+        diffUnique id (fromMaybe "") fn valueLens
+
+    freeTextFieldDef fn valueLens = DiffOptions $
+        diffUnique id id fn valueLens
+
+    freeTextFieldDefST fn valueLens = DiffOptions $
+        diffUnique id fromShortText fn valueLens
+
+    prefixedFields _ _   = pure []
+    knownField _         = pure ()
+    deprecatedSince _  _ = id
+    availableSince _ _   = id
+    removedIn _ _        = id
+    hiddenField          = id
+
+instance OptionsGrammar C.Pretty DiffOptions where
+    metahelp _ = help
+
+    help h (DiffOptions xs) = DiffOptions $ \vals config ->
+        case xs vals config of
+            [] -> []
+            diffString -> ("-- " ++ h) : diffString