Always preserve expanded attribute parameters

src/Nixfmt/Pretty.hs

@@ -358,10 +358,10 @@ instance Pretty Parameter where
   -- param:
   pretty (IDParameter i) = pretty i
   -- {}:
-  pretty (SetParameter bopen [] bclose) =
-    group $ pretty (moveTrailingCommentUp bopen) <> hardspace <> pretty bclose
+  pretty (SetParameter bopen@Ann{sourceLine = openLine} [] bclose@Ann{sourceLine = closeLine}) =
+    group $ pretty (moveTrailingCommentUp bopen) <> (if openLine /= closeLine then hardline else hardspace) <> pretty bclose
   -- { stuff }:
-  pretty (SetParameter bopen attrs bclose) =
+  pretty (SetParameter bopen@Ann{sourceLine = openLine} attrs bclose@Ann{sourceLine = closeLine}) =
     group $
       pretty (moveTrailingCommentUp bopen)
         <> surroundWith sep (nest $ sepBy sep $ handleTrailingComma $ map moveParamAttrComment $ moveParamsComments attrs)
@@ -376,14 +376,17 @@ instance Pretty Parameter where
         [pretty (ParamAttr name maybeDefault Nothing) <> trailing ","]
       handleTrailingComma (x : xs) = pretty x : handleTrailingComma xs
 
-      sep = case attrs of
-        [ParamEllipsis _] -> line
-        -- Attributes must be without default
-        [ParamAttr _ Nothing _] -> line
-        [ParamAttr _ Nothing _, ParamEllipsis _] -> line
-        [ParamAttr _ Nothing _, ParamAttr _ Nothing _] -> line
-        [ParamAttr _ Nothing _, ParamAttr _ Nothing _, ParamEllipsis _] -> line
-        _ -> hardline
+      sep =
+        if openLine /= closeLine
+          then hardline
+          else case attrs of
+            [ParamEllipsis _] -> line
+            -- Attributes must be without default
+            [ParamAttr _ Nothing _] -> line
+            [ParamAttr _ Nothing _, ParamEllipsis _] -> line
+            [ParamAttr _ Nothing _, ParamAttr _ Nothing _] -> line
+            [ParamAttr _ Nothing _, ParamAttr _ Nothing _, ParamEllipsis _] -> line
+            _ -> hardline
   pretty (ContextParameter param1 at param2) =
     pretty param1 <> pretty at <> pretty param2
 

test/diff/idioms_lib_3/out.nix

@@ -12,7 +12,9 @@
 #
 # Tests can be found in ./tests/misc.nix
 # Documentation in the manual, #sec-generators
-{ lib }:
+{
+  lib,
+}:
 with (lib).trivial;
 let
   libStr = lib.strings;
@@ -29,7 +31,8 @@ rec {
   # The builtin `toString` function has some strange defaults,
   # suitable for bash scripts but not much else.
   mkValueStringDefault =
-    { }:
+    {
+    }:
     v:
     with builtins;
     let
@@ -203,7 +206,10 @@ rec {
       # allow lists as values for duplicate keys
       listsAsDuplicateKeys ? false,
     }:
-    { globalSection, sections }:
+    {
+      globalSection,
+      sections,
+    }:
     (
       if globalSection == { } then
         ""
@@ -279,7 +285,10 @@ rec {
 
   # Generates JSON from an arbitrary (non-function) value.
   # For more information see the documentation of the builtin.
-  toJSON = { }: builtins.toJSON;
+  toJSON =
+    {
+    }:
+    builtins.toJSON;
 
   # YAML has been a strict superset of JSON since 1.2, so we
   # use toJSON. Before it only had a few differences referring
@@ -465,7 +474,8 @@ rec {
 
   # PLIST handling
   toPlist =
-    { }:
+    {
+    }:
     v:
     let
       isFloat = builtins.isFloat or (x: false);
@@ -546,7 +556,8 @@ rec {
   # Note that integers are translated to Integer and never
   # the Natural type.
   toDhall =
-    { }@args:
+    {
+    }@args:
     v:
     with builtins;
     let

test/diff/key_value/out.nix

@@ -56,7 +56,12 @@ rec {
       c = 2;
     };
   n = pkgs: { };
-  o = { pkgs, ... }: { };
+  o =
+    {
+      pkgs,
+      ...
+    }:
+    { };
 
   a
     # b

test/diff/lambda/out.nix

@@ -81,15 +81,22 @@ in
 
   (
     a:
-    { b, ... }:
+    {
+      b,
+      ...
+    }:
     c: {
       # Stuff
     }
   )
 
   (
     a:
-    { b, c, ... }:
+    {
+      b,
+      c,
+      ...
+    }:
     d: {
       # Stuff
     }