Make function arguments look more consistent

This change modifies the ‘HsApp’ printer to handle all function parameters
at once instead of following the AST order.

This allows us to consistently put each function argument on separate lines.
Previously, when printing the function f a b c, the AST would look like (((f
a) b) c), which would cause inconsistencies regarding to newlines (imagine f
a\n b).

Otherwise I tried to preserve the same behaviour as the previous printer,
and added a few tests.

This only changes the ‘p_hsExpr’ function, rest of the changes are caused by
the formatting change.

data/examples/declaration/rewrite-rule/basic1-out.hs

@@ -10,7 +10,8 @@
 
 {-# RULES
 "map/map"
-  map f
+  map
+    f
     (map g xs) =
     map
       (f . g)

data/examples/declaration/rewrite-rule/phase-out.hs

@@ -1,6 +1,7 @@
 {-# RULES
 "map/map" [2]
-  map f
+  map
+    f
     (map g xs) =
     map
       (f . g)
@@ -9,7 +10,8 @@
 
 {-# RULES
 "map/map" [1] forall x y z.
-  map f
+  map
+    f
     (map g xs) =
     map
       (f . g)

data/examples/declaration/value/function/application-out.hs

@@ -0,0 +1,17 @@
+foo =
+  f1
+    p1
+    p2
+    p3
+
+foo' =
+  f2
+    p1
+    p2
+    p3
+
+foo'' =
+  f3
+    p1
+    p2
+    p3

data/examples/declaration/value/function/application.hs

@@ -0,0 +1,12 @@
+foo =
+  f1
+    p1
+    p2 p3
+
+foo' = f2 p1
+  p2
+  p3
+
+foo'' =
+  f3 p1 p2
+    p3

data/examples/declaration/value/function/block-arguments-out.hs

@@ -25,3 +25,5 @@ f7 = foo \x -> y
 
 f8 = foo \x ->
   y
+
+f9 = foo do { bar } baz

data/examples/declaration/value/function/block-arguments.hs

@@ -21,3 +21,5 @@ f7 = foo \x -> y
 
 f8 = foo \x ->
   y
+
+f9 = foo do { bar } baz

data/examples/declaration/value/function/static-pointers-out.hs

@@ -14,6 +14,7 @@ bar =
 baz :: StaticPtr Bool
 baz =
   static
-    ( fun 1
+    ( fun
+        1
         2
     )

src/Ormolu/Exception.hs

@@ -51,7 +51,9 @@ instance Exception OrmoluException where
              )
           ++ ["Please, consider reporting the bug."]
     OrmoluNonIdempotentOutput loc left right ->
-      showParsingErr "Formatting is not idempotent:" loc
+      showParsingErr
+        "Formatting is not idempotent:"
+        loc
         ["before: " ++ show left, "after:  " ++ show right]
         ++ "Please, consider reporting the bug.\n"
 

src/Ormolu/Parser/CommentStream.hs

@@ -62,7 +62,8 @@ mkCommentStream extraComments pstate =
       mapMaybe toRealSpan $
         extraComments
           ++ mapMaybe (liftMaybe . fmap unAnnotationComment) (GHC.comment_q pstate)
-          ++ concatMap (mapMaybe (liftMaybe . fmap unAnnotationComment) . snd)
+          ++ concatMap
+            (mapMaybe (liftMaybe . fmap unAnnotationComment) . snd)
             (GHC.annotations_comments pstate)
 
 -- | Test whether a 'Comment' looks like a Haddock following a definition,

src/Ormolu/Printer.hs

@@ -21,7 +21,8 @@ printModule ::
   -- | Resulting rendition
   Text
 printModule ParseResult {..} =
-  runR (p_hsModule prExtensions prParsedSource)
+  runR
+    (p_hsModule prExtensions prParsedSource)
     (mkSpanStream prParsedSource)
     prCommentStream
     prAnns

src/Ormolu/Printer/Meat/Declaration/Value.hs

@@ -19,7 +19,7 @@ import Data.Bool (bool)
 import Data.Char (isPunctuation, isSymbol)
 import Data.Data hiding (Infix, Prefix)
 import Data.List (intersperse, sortOn)
-import Data.List.NonEmpty (NonEmpty ((:|)))
+import Data.List.NonEmpty ((<|), NonEmpty ((:|)))
 import qualified Data.List.NonEmpty as NE
 import Data.Text (Text)
 import qualified Data.Text as Text
@@ -237,7 +237,8 @@ p_match' placer render style isInfix strictness m_pats m_grhss = do
         combineSrcSpans' $
           getGRHSSpan . unLoc <$> NE.fromList grhssGRHSs
       patGrhssSpan =
-        maybe grhssSpan
+        maybe
+          grhssSpan
           (combineSrcSpans grhssSpan . srcLocSpan)
           endOfPats
       placement =
@@ -525,25 +526,44 @@ p_hsExpr' s = \case
     breakpoint
     inci (p_matchGroup LambdaCase mgroup)
   HsApp NoExt f x -> do
-    -- We hang only the last function argument. In order to do this, we only
-    -- call 'placeHanging' on the topmost 'HsApp', and then use
-    -- 'p_withoutHanging' for the descendants.
-    let p_withoutHanging (HsApp NoExt f' x') = do
+    let -- In order to format function applications with multiple parameters
+        -- nicer, traverse the AST to gather the function and all the
+        -- parameters together.
+        gatherArgs f' knownArgs =
           case f' of
-            L _ (HsApp _ _ _) -> located f' p_withoutHanging
-            _ -> located f' (p_hsExpr' s)
-          breakpoint
-          inci $ located x' p_hsExpr
-        p_withoutHanging e = p_hsExpr e
-        -- Only use the hanging placement if the function spans a single
+            L _ (HsApp _ l r) -> gatherArgs l (r <| knownArgs)
+            _ -> (f', knownArgs)
+        (func, args) = gatherArgs f (x :| [])
+        -- We need to handle the last argument specially if it is a
+        -- hanging construct, so separate it from the rest.
+        (initp, lastp) = (NE.init args, NE.last args)
+        initSpan = combineSrcSpans' $ getLoc f :| map getLoc initp
+        -- Hang the last argument only if the initial arguments spans one
         -- line.
         placement =
-          if isOneLineSpan (getLoc f)
-            then exprPlacement (unLoc x)
+          if isOneLineSpan initSpan
+            then exprPlacement (unLoc lastp)
             else Normal
-    useBraces (located f p_withoutHanging)
-    placeHanging placement $
-      located x p_hsExpr
+    -- If the last argument is not hanging, just separate every argument as
+    -- usual. If it is hanging, print the initial arguments and hang the
+    -- last one. Also, use braces around the every argument except the last
+    -- one.
+    case placement of
+      Normal -> do
+        useBraces $ do
+          located func (p_hsExpr' s)
+          breakpoint
+          inci $ sep breakpoint (located' p_hsExpr) initp
+        inci $ do
+          unless (null initp) breakpoint
+          located lastp p_hsExpr
+      Hanging -> do
+        useBraces . switchLayout [initSpan] $ do
+          located func (p_hsExpr' s)
+          breakpoint
+          sep breakpoint (located' p_hsExpr) initp
+        placeHanging placement $
+          located lastp p_hsExpr
   HsAppType a e -> do
     located e p_hsExpr
     breakpoint
@@ -1089,7 +1109,8 @@ p_stringLit src =
     zipPrevNext :: [a] -> [(Maybe a, a, Maybe a)]
     zipPrevNext xs =
       let z =
-            zip (zip (Nothing : map Just xs) xs)
+            zip
+              (zip (Nothing : map Just xs) xs)
               (map Just (tail xs) ++ repeat Nothing)
        in map (\((p, x), n) -> (p, x, n)) z
     orig (_, x, _) = x

src/Ormolu/Printer/Meat/Type.hs

@@ -191,7 +191,8 @@ p_conDeclField :: ConDeclField GhcPs -> R ()
 p_conDeclField ConDeclField {..} = do
   mapM_ (p_hsDocString Pipe True) cd_fld_doc
   sitcc $
-    sep (comma >> breakpoint)
+    sep
+      (comma >> breakpoint)
       (located' (p_rdrName . rdrNameFieldOcc))
       cd_fld_names
   space