treewide: use whenJust

Author: Anton-Latukha

.hlint.yaml

@@ -2686,3 +2686,7 @@
     lhs: "Data.Bool.bool True"
     rhs: "Use `whenTrue` from HNix Prelude"
 
+- hint:
+    lhs: "maybe mempty"
+    note: "Use `whenJust`"
+    rhs: whenJust

src/Nix/Builtins.hs

@@ -207,10 +207,7 @@ foldNixPath z f =
       go
       z
       $ (fromInclude . stringIgnoreContext <$> dirs)
-        <> maybe
-            mempty
-            uriAwareSplit
-            mPath
+        <> uriAwareSplit `whenJust` mPath
         <> [ fromInclude $ "nix=" <> toText dataDir <> "/nix/corepkgs" ]
  where
 

src/Nix/Pretty.hs

@@ -132,15 +132,14 @@ prettyParams :: Params (NixDoc ann) -> Doc ann
 prettyParams (Param n           ) = prettyVarName n
 prettyParams (ParamSet mname variadic pset) =
   prettyParamSet variadic pset <>
-    maybe
+     toDoc `whenJust` mname
+ where
+  toDoc :: VarName -> Doc ann
+  toDoc (coerce -> name) =
+    bool
       mempty
-      (\ (coerce -> name) ->
-        bool
-          mempty
-          ("@" <> pretty name)
-          (not (Text.null name))
-      )
-      mname
+      ("@" <> pretty name)
+      (not (Text.null name))
 
 prettyParamSet :: Variadic -> ParamSet (NixDoc ann) -> Doc ann
 prettyParamSet variadic args =
@@ -164,10 +163,7 @@ prettyBind (Inherit s ns _p) =
   "inherit " <> scope <> align (fillSep $ prettyVarName <$> ns) <> ";"
   where
     scope =
-      maybe
-        mempty
-        ((<> " ") . parens . withoutParens)
-        s
+      ((<> " ") . parens . withoutParens) `whenJust` s
 
 prettyKeyName :: NKeyName (NixDoc ann) -> Doc ann
 prettyKeyName (StaticKey "") = "\"\""
@@ -255,10 +251,7 @@ exprFNixDoc = \case
    where
     r     = mkNixDoc selectOp (wrapParens appOpNonAssoc r')
     ordoc =
-      maybe
-        mempty
-        ((" or " <>) . wrapParens appOpNonAssoc)
-        o
+      ((" or " <>) . wrapParens appOpNonAssoc) `whenJust` o
   NHasAttr r attr ->
     mkNixDoc hasAttrOp (wrapParens hasAttrOp r <> " ? " <> prettySelector attr)
   NEnvPath     p -> simpleExpr $ pretty @String $ coerce $ "<" <> p <> ">"

src/Nix/Render/Frame.hs

@@ -55,10 +55,7 @@ renderFrames (x : xs) = do
  where
   go :: NixFrame -> [Doc ann]
   go f =
-    maybe
-      mempty
-      (\ pos -> ["While evaluating at " <> pretty (sourcePosPretty pos) <> colon])
-      (framePos @v @m f)
+    (\ pos -> ["While evaluating at " <> pretty (sourcePosPretty pos) <> colon]) `whenJust` framePos @v @m f
 
 framePos
   :: forall v (m :: Type -> Type)

src/Nix/TH.hs

@@ -68,7 +68,7 @@ freeVars e = case unFix e of
     Set.unions
       [ freeVars expr
       , pathFree path
-      , maybe mempty freeVars orExpr
+      , freeVars `whenJust` orExpr
       ]
   (NHasAttr expr            path) -> freeVars expr <> pathFree path
   (NAbs     (Param varname) expr) -> Set.delete varname (freeVars expr)
@@ -79,7 +79,7 @@ freeVars e = case unFix e of
     Set.difference
       (Set.unions $ freeVars <$> mapMaybe snd pset)
       (Set.difference
-        (maybe mempty one varname)
+        (one `whenJust` varname)
         (Set.fromList $ fst <$> pset)
       )
   (NLet         bindings expr   ) ->

src/Nix/Utils.hs

@@ -195,11 +195,10 @@ whenJust
   => (a -> b)
   -> Maybe a
   -> b
-whenJust f ma =
+whenJust =
   maybe
     mempty
-    f
-    ma
+{-# inline whenJust #-}
 
 
 -- | Apply a single function to both components of a pair.

src/Nix/XML.hs

@@ -111,10 +111,7 @@ paramsXML (ParamSet mname variadic pset) =
       [ Attr (unqual "ellipsis") "1" ]
       (variadic == Variadic)
   nattr =
-    maybe
-      mempty
-      ((: mempty) . Attr (unqual "name") . toString)
-      mname
+    ((: mempty) . Attr (unqual "name") . toString) `whenJust` mname
 
 paramSetXML :: ParamSet r -> [Content]
 paramSetXML = fmap (\(k, _) -> Elem $ mkEName "attr" (toString k))