Always preserve expanded attribute sets

src/Nixfmt/Pretty.hs

@@ -162,25 +162,33 @@ prettySet
   _
   ( krec,
     paropen@Ann
-      { preTrivia = [],
+      { sourceLine = openLine,
+        preTrivia = [],
         trailComment = Nothing
       },
     Items [],
     parclose@Ann
-      { preTrivia = []
+      { sourceLine = closeLine,
+        preTrivia = []
       }
     ) =
-    pretty (fmap (,hardspace) krec) <> pretty paropen <> hardspace <> pretty parclose
+    pretty (fmap (,hardspace) krec) <> pretty paropen <> sep <> pretty parclose
+    where
+      -- If the braces are on different lines, keep them like that
+      sep = if openLine /= closeLine then hardline else hardspace
 -- Singleton sets are allowed to fit onto one line,
 -- but apart from that always expand.
 prettySet
   wide
   ( krec,
     paropen@Ann
-      { trailComment = post
+      { sourceLine = openLine,
+        trailComment = post
       },
     binders,
-    parclose
+    parclose@Ann
+      { sourceLine = closeLine
+      }
     ) =
     pretty (fmap (,hardspace) krec)
       <> pretty (paropen{trailComment = Nothing})
@@ -189,6 +197,8 @@ prettySet
     where
       sep =
         if wide && not (null (unItems binders))
+          -- If the braces are on different lines, keep them like that
+          || openLine /= closeLine
           then hardline
           else line
 

test/diff/apply/out.nix

@@ -113,17 +113,25 @@
     name3 = function arg { asdf = 1; } { qwer = 12345; } argument;
   }
   {
-    name1 = function arg { asdf = 1; };
+    name1 = function arg {
+      asdf = 1;
+    };
 
     name2 = function arg {
       asdf = 1;
       # multiline
     } argument;
 
-    name3 = function arg {
-      asdf = 1;
-      # multiline
-    } { qwer = 12345; } argument;
+    name3 =
+      function arg
+        {
+          asdf = 1;
+          # multiline
+        }
+        {
+          qwer = 12345;
+        }
+        argument;
   }
   {
     name4 = function arg { asdf = 1; } {

test/diff/attr_set/out.nix

@@ -4,7 +4,9 @@
     # a
   }
   { a = 1; }
-  { a = 1; }
+  {
+    a = 1;
+  }
 
   {
 

test/diff/idioms_lib_3/out.nix

@@ -263,9 +263,13 @@ rec {
             if isAttrs value && !lib.isDerivation value then
               lib.mapAttrsToList (name: value: recurse ([ name ] ++ path) value) value
             else if length path > 1 then
-              { ${concatStringsSep "." (lib.reverseList (tail path))}.${head path} = value; }
+              {
+                ${concatStringsSep "." (lib.reverseList (tail path))}.${head path} = value;
+              }
             else
-              { ${head path} = value; };
+              {
+                ${head path} = value;
+              };
         in
         attrs: lib.foldl lib.recursiveUpdate { } (lib.flatten (recurse [ ] attrs));
 

test/diff/idioms_nixos_2/out.nix

@@ -51,7 +51,10 @@ let
       post_max_size = cfg.maxUploadSize;
       memory_limit = cfg.maxUploadSize;
     }
-    // cfg.phpOptions // optionalAttrs cfg.caching.apcu { "apc.enable_cli" = "1"; };
+    // cfg.phpOptions
+    // optionalAttrs cfg.caching.apcu {
+      "apc.enable_cli" = "1";
+    };
 
   occ = pkgs.writeScriptBin "nextcloud-occ" ''
     #! ${pkgs.runtimeShell}

test/diff/idioms_pkgs_1/out.nix

@@ -8,7 +8,9 @@
 stdenv.mkDerivation rec {
   pname = "test";
   version = "0.0";
-  src = fetchFrom { url = "example/${version}"; };
+  src = fetchFrom {
+    url = "example/${version}";
+  };
   meta = with lib; {
     maintainers = with maintainers; [ someone ];
     description = "something";

test/diff/idioms_pkgs_4/out.nix

@@ -197,9 +197,13 @@ in
   # First build a stdenv based only on tools outside the store.
   (prevStage: {
     inherit config overlays;
-    stdenv = makeStdenv { inherit (prevStage) cc fetchurl; } // {
-      inherit (prevStage) fetchurl;
-    };
+    stdenv =
+      makeStdenv {
+        inherit (prevStage) cc fetchurl;
+      }
+      // {
+        inherit (prevStage) fetchurl;
+      };
   })
 
   # Using that, build a stdenv that adds the ‘xz’ command (which most systems

test/diff/idioms_pkgs_5/out.nix

@@ -628,9 +628,14 @@ let
             enableParallelChecking = attrs.enableParallelChecking or true;
             enableParallelInstalling = attrs.enableParallelInstalling or true;
           }
-          // optionalAttrs (
-            hardeningDisable != [ ] || hardeningEnable != [ ] || stdenv.hostPlatform.isMusl
-          ) { NIX_HARDENING_ENABLE = enabledHardeningOptions; }
+          //
+            optionalAttrs
+              (
+                hardeningDisable != [ ] || hardeningEnable != [ ] || stdenv.hostPlatform.isMusl
+              )
+              {
+                NIX_HARDENING_ENABLE = enabledHardeningOptions;
+              }
           //
             optionalAttrs (stdenv.hostPlatform.isx86_64 && stdenv.hostPlatform ? gcc.arch)
               {

test/diff/if_else/out.nix

@@ -1,5 +1,14 @@
 [
-  (if true then { version = "1.2.3"; } else { version = "3.2.1"; })
+  (
+    if true then
+      {
+        version = "1.2.3";
+      }
+    else
+      {
+        version = "3.2.1";
+      }
+  )
   (
     if true then
       ''

test/diff/inherit/out.nix

@@ -18,7 +18,9 @@
       j
       ;
   }
-  { inherit aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa; }
+  {
+    inherit aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa;
+  }
   { inherit b d; }
   {
     inherit

test/diff/with/out.nix

@@ -89,7 +89,9 @@
       b = 2;
     }
   )
-  { a = with b; with b; with b; 1; }
+  {
+    a = with b; with b; with b; 1;
+  }
   {
     binPath =
       with pkgs;