Always preserve expanded lists

src/Nixfmt/Pretty.hs

@@ -231,27 +231,37 @@ prettyTerm (Selection term selectors rest) =
 prettyTerm
   ( List
       paropen@Ann
-        { trailComment = Nothing
+        { sourceLine = openLine,
+          trailComment = Nothing
         }
       (Items [])
       parclose@Ann
-        { preTrivia = []
+        { sourceLine = closeLine,
+          preTrivia = []
         }
     ) =
-    pretty paropen <> hardspace <> pretty parclose
+    pretty paropen <> sep <> pretty parclose
+    where
+      -- If the brackets are on different lines, keep them like that
+      sep = if openLine /= closeLine then hardline else hardspace
 -- General list
 -- Always expand if len > 1
 prettyTerm
   ( List
       paropen@Ann
-        { trailComment = post
+        { sourceLine = openLine,
+          trailComment = post
         }
       items
-      parclose
+      parclose@Ann
+        { sourceLine = closeLine
+        }
     ) =
     pretty (paropen{trailComment = Nothing})
-      <> surroundWith line (nest $ pretty post <> prettyItems items)
+      <> surroundWith sur (nest $ pretty post <> prettyItems items)
       <> pretty parclose
+    where
+      sur = if openLine /= closeLine then hardline else line
 prettyTerm (Set krec paropen items parclose) = prettySet False (krec, paropen, items, parclose)
 -- Parentheses
 prettyTerm (Parenthesized paropen expr parclose@(Ann{preTrivia = closePre})) =

test/diff/idioms_pkgs_3/out.nix

@@ -237,7 +237,9 @@ buildStdenv.mkDerivation ({
 
   inherit src unpackPhase meta;
 
-  outputs = [ "out" ] ++ lib.optionals crashreporterSupport [ "symbols" ];
+  outputs = [
+    "out"
+  ] ++ lib.optionals crashreporterSupport [ "symbols" ];
 
   # Add another configure-build-profiling run before the final configure phase if we build with pgo
   preConfigurePhases = lib.optionals pgoSupport [

test/diff/idioms_pkgs_4/out.nix

@@ -84,9 +84,13 @@ let
     ]
     ++ (
       if system == "i686-cygwin" then
-        [ ../cygwin/rebase-i686.sh ]
+        [
+          ../cygwin/rebase-i686.sh
+        ]
       else if system == "x86_64-cygwin" then
-        [ ../cygwin/rebase-x86_64.sh ]
+        [
+          ../cygwin/rebase-x86_64.sh
+        ]
       else
         [ ]
     );

test/diff/lists/out.nix

@@ -46,7 +46,9 @@
   ]
   [ 1 ]
 
-  [ 1 ]
+  [
+    1
+  ]
 
   [
     b

test/diff/operation/out.nix

@@ -230,7 +230,9 @@
       zip
       zlib
     ]
-    ++ [ (if (lib.versionAtLeast version "103") then nss_latest else nss_esr) ]
+    ++ [
+      (if (lib.versionAtLeast version "103") then nss_latest else nss_esr)
+    ]
   )
 
   # Indentation with parenthesized multiline function call