From c10c061713782067e6ae6f90210f10d0aa6366ba Mon Sep 17 00:00:00 2001
From: Silvan Mosberger <contact@infinisil.com>
Date: Fri, 19 Jul 2024 06:53:22 +0200
Subject: [PATCH] Always preserve expanded inherits

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

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

An example of this is inheriting from `lib`, which usually starts out
with just a single value, but usually gets more later. This would've been
contracted onto a single line before this change:

    inherit (lib)
      foo
      ;

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                | 14 ++++++++++----
 test/diff/inherit/in.nix            |  9 +++++++++
 test/diff/inherit/out-pure.nix      |  6 ++++++
 test/diff/inherit/out.nix           | 14 +++++++++++++-
 test/diff/inherit_from/in.nix       | 13 +++++++++++++
 test/diff/inherit_from/out-pure.nix |  9 +++++++++
 test/diff/inherit_from/out.nix      | 13 +++++++++++++
 7 files changed, 73 insertions(+), 5 deletions(-)

diff --git a/src/Nixfmt/Pretty.hs b/src/Nixfmt/Pretty.hs
index d4a2497c..88892ea2 100644
--- a/src/Nixfmt/Pretty.hs
+++ b/src/Nixfmt/Pretty.hs
@@ -129,8 +129,11 @@ instance Pretty Binder where
       pretty inherit
         <> ( if null ids
               then pretty semicolon
-              else line <> nest (sepBy (if length ids < 4 then line else hardline) ids <> line' <> pretty semicolon)
+              else sep <> nest (sepBy sep ids <> nosep <> pretty semicolon)
            )
+    where
+      -- Only allow a single line if it's already on a single line and has few enough elements
+      (sep, nosep) = if sourceLine inherit == sourceLine semicolon && length ids < 4 then (line, line') else (hardline, hardline)
   -- `inherit (foo) bar` statement
   pretty (Inherit inherit (Just source) ids semicolon) =
     group $
@@ -140,11 +143,14 @@ instance Pretty Binder where
               <> if null ids
                 then pretty semicolon
                 else
-                  line
-                    <> sepBy (if length ids < 4 then line else hardline) ids
-                    <> line'
+                  sep
+                    <> sepBy sep ids
+                    <> nosep
                     <> pretty semicolon
           )
+    where
+      -- Only allow a single line if it's already on a single line and has few enough elements
+      (sep, nosep) = if sourceLine inherit == sourceLine semicolon && length ids < 4 then (line, line') else (hardline, hardline)
   -- `foo = bar`
   pretty (Assignment selectors assign expr semicolon) =
     group $
diff --git a/test/diff/inherit/in.nix b/test/diff/inherit/in.nix
index a66fc107..a5088d4c 100644
--- a/test/diff/inherit/in.nix
+++ b/test/diff/inherit/in.nix
@@ -29,4 +29,13 @@
       h
       ;
   }
+
+  {
+    inherit
+      ;
+    inherit
+      a;
+    inherit a
+      ;
+  }
 ]
diff --git a/test/diff/inherit/out-pure.nix b/test/diff/inherit/out-pure.nix
index 93a31869..307e32ab 100644
--- a/test/diff/inherit/out-pure.nix
+++ b/test/diff/inherit/out-pure.nix
@@ -77,4 +77,10 @@
       h
       ;
   }
+
+  {
+    inherit;
+    inherit a;
+    inherit a;
+  }
 ]
diff --git a/test/diff/inherit/out.nix b/test/diff/inherit/out.nix
index 77e5e873..a5b01067 100644
--- a/test/diff/inherit/out.nix
+++ b/test/diff/inherit/out.nix
@@ -19,7 +19,9 @@
       ;
   }
   {
-    inherit aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa;
+    inherit
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+      ;
   }
   { inherit b d; }
   {
@@ -79,4 +81,14 @@
       h
       ;
   }
+
+  {
+    inherit;
+    inherit
+      a
+      ;
+    inherit
+      a
+      ;
+  }
 ]
diff --git a/test/diff/inherit_from/in.nix b/test/diff/inherit_from/in.nix
index 6b375f1c..ea9d0e6e 100644
--- a/test/diff/inherit_from/in.nix
+++ b/test/diff/inherit_from/in.nix
@@ -75,4 +75,17 @@
   { inherit /*a*/ (/*b*/ c /*d*/) /*e*/ f       h /*i*/; }
   { inherit /*a*/ (/*b*/ c /*d*/) /*e*/ f /*g*/ h      ; }
   { inherit /*a*/ (/*b*/ c /*d*/) /*e*/ f /*g*/ h /*i*/; }
+  {
+    inherit ({}) ;
+    inherit ({})
+      ;
+    inherit
+      ({});
+
+    inherit ({}) a;
+    inherit ({}) a
+      ;
+    inherit ({})
+      a;
+  }
 ]
diff --git a/test/diff/inherit_from/out-pure.nix b/test/diff/inherit_from/out-pure.nix
index 126b8f8b..58be059f 100644
--- a/test/diff/inherit_from/out-pure.nix
+++ b/test/diff/inherit_from/out-pure.nix
@@ -571,4 +571,13 @@
       h # i
       ;
   }
+  {
+    inherit ({ });
+    inherit ({ });
+    inherit ({ });
+
+    inherit ({ }) a;
+    inherit ({ }) a;
+    inherit ({ }) a;
+  }
 ]
diff --git a/test/diff/inherit_from/out.nix b/test/diff/inherit_from/out.nix
index 126b8f8b..62225bbc 100644
--- a/test/diff/inherit_from/out.nix
+++ b/test/diff/inherit_from/out.nix
@@ -571,4 +571,17 @@
       h # i
       ;
   }
+  {
+    inherit ({ });
+    inherit ({ });
+    inherit ({ });
+
+    inherit ({ }) a;
+    inherit ({ })
+      a
+      ;
+    inherit ({ })
+      a
+      ;
+  }
 ]