Make sure variables are not leaking from with

Closes #4123.

Author: lexmag

lib/elixir/src/elixir_with.erl

@@ -44,7 +44,8 @@ expand(X, E) ->
 translate(_Meta, Args, S) ->
   {Parts, [{do, Expr} | _Opts]} = elixir_utils:split_last(Args),
   Cases = build_cases(Parts, Expr),
-  elixir_translator:translate(Cases, S).
+  {TC, TS} = elixir_translator:translate(Cases, S),
+  {TC, elixir_scope:mergec(S, TS)}.
 
 build_cases([{'<-', Meta, [Left, Right]} | Rest], DoExpr) ->
   Other = {'other', Meta, nil},

lib/elixir/test/elixir/kernel/expansion_test.exs

@@ -264,6 +264,9 @@ defmodule Kernel.ExpansionTest do
   test "variables inside with do not leak" do
     assert expand(quote do: (with(a <- b, do: c = 1); c)) ==
            quote do: (with(a <- b(), do: c = 1); c())
+
+    assert expand(quote do: (with(a = b, do: a); a)) ==
+           quote do: (with(a = b(), do: a); a())
   end
 
   test "variables inside with are available in blocks" do