From 93e65f499f4fe92d85bc97d6a5d78f670e557208 Mon Sep 17 00:00:00 2001
From: preciz <barna.kovacs@tutanota.com>
Date: Wed, 26 Aug 2026 13:15:31 +0200
Subject: [PATCH] Concatenate query list field once

---
 lib/plug/conn/query.ex | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/lib/plug/conn/query.ex b/lib/plug/conn/query.ex
index 5f436190..90d58af1 100644
--- a/lib/plug/conn/query.ex
+++ b/lib/plug/conn/query.ex
@@ -427,19 +427,17 @@ defmodule Plug.Conn.Query do
 
   # covers non-keyword lists
   defp encode_pair(parent_field, list, encoder) when is_list(list) do
-    mapper = fn
+    field = parent_field <> "[]"
+
+    Enum.map_intersperse(list, ?&, fn
       value when is_map(value) and map_size(value) != 1 ->
         raise ArgumentError,
               "cannot encode maps inside lists when the map has 0 or more than 1 element, " <>
                 "got: #{inspect(value)}"
 
       value ->
-        [?&, encode_pair(parent_field <> "[]", value, encoder)]
-    end
-
-    list
-    |> Enum.flat_map(mapper)
-    |> prune()
+        encode_pair(field, value, encoder)
+    end)
   end
 
   # covers nil