Add explicit strategies to deriving clauses

Problem:  The `deriving ($classes...)` is becoming obsolete.

Solution: Replace with `deriving $strat ($classes...)`;
          make old deriving a warning.

links-tests/Test/Xrefcheck/FtpLinks.hs

@@ -29,7 +29,7 @@ ftpOptions =
 
 -- | Option specifying FTP host.
 newtype FtpHostOpt = FtpHostOpt Text
-  deriving (Show, Eq)
+  deriving stock (Show, Eq)
 
 instance IsOption FtpHostOpt where
   defaultValue = FtpHostOpt "ftp://localhost"

package.yaml

@@ -55,6 +55,7 @@ ghc-options:
   - -Wall
   - -Wincomplete-record-updates
   - -Wincomplete-uni-patterns
+  - -Wmissing-deriving-strategies
 
 dependencies:
   - aeson

src/Xrefcheck/Core.hs

@@ -40,7 +40,7 @@ import Data.DList qualified as DList
 data Flavor
   = GitHub
   | GitLab
-  deriving (Show)
+  deriving stock (Show)
 
 allFlavors :: [Flavor]
 allFlavors = [GitHub, GitLab]
@@ -61,7 +61,7 @@ instance FromJSON Flavor where
 -- We keep this in text because scanners for different formats use different
 -- representation of this thing, and it actually appears in reports only.
 newtype Position = Position (Maybe Text)
-  deriving (Show, Eq, Generic)
+  deriving stock (Show, Eq, Generic)
 
 instance Buildable Position where
   build (Position pos) = case pos of
@@ -77,7 +77,7 @@ data Reference = Reference
   , rAnchor :: Maybe Text
     -- ^ Section or custom anchor tag.
   , rPos    :: Position
-  } deriving (Show, Generic)
+  } deriving stock (Show, Generic)
 
 -- | Context of anchor.
 data AnchorType
@@ -87,14 +87,14 @@ data AnchorType
     -- ^ They can be set up manually
   | BiblioAnchor
     -- ^ Id of entry in bibliography
-  deriving (Show, Eq, Generic)
+  deriving stock (Show, Eq, Generic)
 
 -- | A referable anchor.
 data Anchor = Anchor
   { aType :: AnchorType
   , aName :: Text
   , aPos  :: Position
-  } deriving (Show, Eq, Generic)
+  } deriving stock (Show, Eq, Generic)
 
 data FileInfoDiff = FileInfoDiff
   { _fidReferences :: DList Reference
@@ -116,14 +116,14 @@ instance Monoid FileInfoDiff where
 data FileInfo = FileInfo
   { _fiReferences :: [Reference]
   , _fiAnchors    :: [Anchor]
-  } deriving (Show, Generic)
+  } deriving stock (Show, Generic)
 makeLenses ''FileInfo
 
 instance Default FileInfo where
   def = diffToFileInfo mempty
 
 newtype RepoInfo = RepoInfo (Map FilePath FileInfo)
-  deriving (Show)
+  deriving stock (Show)
 
 -----------------------------------------------------------
 -- Instances
@@ -189,7 +189,7 @@ data LocationType
     -- ^ Reference to a file at outer site
   | OtherLoc
     -- ^ Entry not to be processed (e.g. "mailto:e-mail")
-  deriving (Show)
+  deriving stock (Show)
 
 instance Buildable LocationType where
   build = \case
@@ -303,7 +303,7 @@ canonizeLocalRef ref =
 data VerifyProgress = VerifyProgress
   { vrLocal    :: !(Progress Int)
   , vrExternal :: !(Progress Int)
-  } deriving (Show)
+  } deriving stock (Show)
 
 initVerifyProgress :: [Reference] -> VerifyProgress
 initVerifyProgress references = VerifyProgress

src/Xrefcheck/Orphans.hs

@@ -44,4 +44,4 @@ instance Buildable FTPException where
   build (UnsuccessfulException e) = build e
   build (BogusResponseFormatException e) = build e
 
-deriving instance Eq FTPException
+deriving stock instance Eq FTPException

src/Xrefcheck/Progress.hs

@@ -36,7 +36,7 @@ data Progress a = Progress
     -- ^ Overall amount of work.
   , pErrors  :: !a
     -- ^ How many of the completed work finished with an error.
-  } deriving (Show)
+  } deriving stock (Show)
 
 -- | Initialise null progress.
 initProgress :: Num a => a -> Progress a

src/Xrefcheck/Scanners/Markdown.hs

@@ -73,7 +73,7 @@ data IgnoreMode
   | Paragraph
   | File
   | None
-  deriving Eq
+  deriving stock (Eq)
 
 -- | A fold over a `Node`.
 cataNode :: (Maybe PosInfo -> NodeType -> [c] -> c) -> Node -> c

src/Xrefcheck/Verify.hs

@@ -64,10 +64,10 @@ import Xrefcheck.System
 -----------------------------------------------------------
 
 newtype VerifyResult e = VerifyResult [e]
-  deriving (Show, Eq, Functor)
+  deriving newtype (Show, Eq, Functor)
 
-deriving instance Semigroup (VerifyResult e)
-deriving instance Monoid (VerifyResult e)
+deriving newtype instance Semigroup (VerifyResult e)
+deriving newtype instance Monoid (VerifyResult e)
 
 instance Buildable e => Buildable (VerifyResult e) where
   build vr = case verifyErrors vr of
@@ -114,7 +114,7 @@ data VerifyError
   | ExternalFtpException FTPException
   | FtpEntryDoesNotExist FilePath
   | ExternalResourceSomeError Text
-  deriving (Show, Eq)
+  deriving stock (Show, Eq)
 
 instance Buildable VerifyError where
   build = \case