From 5082aecd4a647e3c4b018dde594dcaf17fd510a4 Mon Sep 17 00:00:00 2001
From: Silvan Mosberger <contact@infinisil.com>
Date: Fri, 19 Jul 2024 03:44:45 +0200
Subject: [PATCH] Always preserve expanded attribute parameters

This changes the formatting to take into account whether attribute
parameters are expanded onto multiple lines already,
and if so, preserves that.

This is desirable because if a user writes an attribute parameter over
multiple lines, there's most likely an intention to add more attributes,
which would become harder when formatted.

An example of this is package recipes, which usually start out with just a
single attribute argument, but usually get more later. This would've been
contracted onto a single line before this change:

    {
      stdenv,
    }:

This change conforms to the standard due to this line:

> The formatter may take the input formatting into account in some cases in order to preserve multi-line syntax elements (which would otherwise have been contracted by the rules).
---
 src/Nixfmt/Pretty.hs           | 23 ++++++++++++++---------
 test/diff/idioms_lib_3/out.nix | 23 +++++++++++++++++------
 test/diff/key_value/out.nix    |  7 ++++++-
 test/diff/lambda/in.nix        |  7 +++++++
 test/diff/lambda/out.nix       | 24 ++++++++++++++++++++++--
 5 files changed, 66 insertions(+), 18 deletions(-)

diff --git a/src/Nixfmt/Pretty.hs b/src/Nixfmt/Pretty.hs
index 5f4f9663..20784294 100644
--- a/src/Nixfmt/Pretty.hs
+++ b/src/Nixfmt/Pretty.hs
@@ -315,7 +315,9 @@ instance Pretty Parameter where
   pretty (IDParameter i) = pretty i
   -- {}:
   pretty (SetParameter bopen [] bclose) =
-    group $ pretty (moveTrailingCommentUp bopen) <> hardspace <> pretty bclose
+    group $ pretty (moveTrailingCommentUp bopen) <> sep <> pretty bclose
+    where
+      sep = if sourceLine bopen /= sourceLine bclose then hardline else hardspace
   -- { stuff }:
   pretty (SetParameter bopen attrs bclose) =
     group $
@@ -332,14 +334,17 @@ 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 sourceLine bopen /= sourceLine bclose
+          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
 
diff --git a/test/diff/idioms_lib_3/out.nix b/test/diff/idioms_lib_3/out.nix
index 74813d4f..4a1b2843 100644
--- a/test/diff/idioms_lib_3/out.nix
+++ b/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
diff --git a/test/diff/key_value/out.nix b/test/diff/key_value/out.nix
index 1d93de5b..0ced3361 100644
--- a/test/diff/key_value/out.nix
+++ b/test/diff/key_value/out.nix
@@ -56,7 +56,12 @@ rec {
       c = 2;
     };
   n = pkgs: { };
-  o = { pkgs, ... }: { };
+  o =
+    {
+      pkgs,
+      ...
+    }:
+    { };
 
   a
     # b
diff --git a/test/diff/lambda/in.nix b/test/diff/lambda/in.nix
index 12d30655..0f7f7a5c 100644
--- a/test/diff/lambda/in.nix
+++ b/test/diff/lambda/in.nix
@@ -2,6 +2,13 @@ let
   inherit lib;
 in
 [
+  ({}: null)
+  ({
+   }: null)
+  ({
+
+   }: null)
+
   (
     { lib, }:
     let
diff --git a/test/diff/lambda/out.nix b/test/diff/lambda/out.nix
index 64078167..16eb44de 100644
--- a/test/diff/lambda/out.nix
+++ b/test/diff/lambda/out.nix
@@ -2,6 +2,19 @@ let
   inherit lib;
 in
 [
+  ({ }: null)
+  (
+    {
+    }:
+    null
+  )
+  (
+    {
+
+    }:
+    null
+  )
+
   (
     { lib }:
     let
@@ -81,7 +94,10 @@ in
 
   (
     a:
-    { b, ... }:
+    {
+      b,
+      ...
+    }:
     c: {
       # Stuff
     }
@@ -89,7 +105,11 @@ in
 
   (
     a:
-    { b, c, ... }:
+    {
+      b,
+      c,
+      ...
+    }:
     d: {
       # Stuff
     }