Tweak absorbtion rules on bindings with Operation RHS

Fixes #198.

This is a hotfix that should exclude the most common ugly case people
might run into, if this comes up again we should more thoroughly rethink
the rules for this case.

src/Nixfmt/Pretty.hs

@@ -600,7 +600,11 @@ absorbRHS expr = case expr of
   -- Special case `//` and `++` operations to be more compact in some cases
   -- Case 1: two arguments, LHS is absorbable term, RHS fits onto the last line
   (Operation (Term t) (LoneAnn op) b)
-    | isAbsorbable t && isUpdateOrConcat op ->
+    | isAbsorbable t
+        && isUpdateOrConcat op
+        -- Exclude further operations on the RHS
+        -- Hotfix for https://github.com/NixOS/nixfmt/issues/198
+        && case b of (Operation{}) -> False; _ -> True ->
         group' RegularG $ line <> group' Priority (prettyTermWide t) <> line <> pretty op <> hardspace <> pretty b
   -- Case 2a: LHS fits onto first line, RHS is an absorbable term
   (Operation l (LoneAnn op) (Term t))

test/diff/idioms_nixos_2/out-pure.nix

@@ -51,7 +51,8 @@ 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}