From 9cdb25737cadc6b3aa99df45a75c2d6bad3f4511 Mon Sep 17 00:00:00 2001
From: Lukasz Samson <lukaszsamson@gmail.com>
Date: Mon, 9 Nov 2026 12:03:30 +0100
Subject: [PATCH] Preserve variable versions in cond boolean optimization

Assisted-by: Codex:GPT-6.1 sol
---
 lib/elixir/src/elixir_erl_pass.erl            |  5 +++--
 lib/elixir/test/elixir/kernel/macros_test.exs | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/lib/elixir/src/elixir_erl_pass.erl b/lib/elixir/src/elixir_erl_pass.erl
index 0bf6e6b0971..e95f82f6c37 100644
--- a/lib/elixir/src/elixir_erl_pass.erl
+++ b/lib/elixir/src/elixir_erl_pass.erl
@@ -399,8 +399,9 @@ build_truthy_clause(Meta, Condition, Body, S) ->
 %% In case a variable is defined to match in a condition
 %% but a condition returns boolean, we can replace the
 %% variable directly by the boolean result.
-returns_boolean({'=', _, [{Var, _, Ctx}, Condition]}, {Var, _, Ctx}) when is_atom(Var), is_atom(Ctx) ->
-  case elixir_utils:returns_boolean(Condition) of
+returns_boolean({'=', _, [{Var, VarMeta, Ctx}, Condition]}, {Var, BodyMeta, Ctx}) when is_atom(Var), is_atom(Ctx) ->
+  case elixir_utils:returns_boolean(Condition) andalso
+       lists:keyfind(version, 1, VarMeta) =:= lists:keyfind(version, 1, BodyMeta) of
     true  -> {Condition, true};
     false -> false
   end;
diff --git a/lib/elixir/test/elixir/kernel/macros_test.exs b/lib/elixir/test/elixir/kernel/macros_test.exs
index c83e0b052c9..89bbf6fbc28 100644
--- a/lib/elixir/test/elixir/kernel/macros_test.exs
+++ b/lib/elixir/test/elixir/kernel/macros_test.exs
@@ -17,6 +17,21 @@ defmodule Kernel.MacrosTest.Nested do
     end
   end
 
+  defmacro outer_cond do
+    quote do
+      x = :outer_value
+      Kernel.MacrosTest.Nested.inner_cond(x)
+    end
+  end
+
+  defmacro inner_cond(body) do
+    quote do
+      cond do
+        x = is_integer(1) -> unquote(body)
+      end
+    end
+  end
+
   defmacro wrap_empty_var(expr) do
     empty = Macro.var(:"", nil)
 
@@ -76,6 +91,10 @@ defmodule Kernel.MacrosTest do
     assert Nested.value() == 1
   end
 
+  test "cond preserves hygienically distinct variables in the body" do
+    assert Nested.outer_cond() == :outer_value
+  end
+
   test "local with private macro" do
     assert my_private_macro() == 4
   end