Warn if an outdated lexical tracker is given on eval

4 files changed, 43 insertions, 4 deletions

diff --git a/lib/elixir/lib/macro/env.ex b/lib/elixir/lib/macro/env.ex
index 122d1025c..3c23c2aac 100644
--- a/lib/elixir/lib/macro/env.ex
+++ b/lib/elixir/lib/macro/env.ex
@@ -107,6 +107,19 @@ defmodule Macro.Env do
   end
 
   @doc """
+  Prunes compile information from the environment.
+
+  This happens when the environment is captured at compilation
+  time, for example, in the module body, and then used to
+  evaluate code after the module has been defined.
+  """
+  @doc since: "1.14.0"
+  @spec prune_compile_info(t) :: t
+  def prune_compile_info(env) do
+    %{env | lexical_tracker: nil, tracers: []}
+  end
+
+  @doc """
   Returns a list of variables in the current environment.
 
   Each variable is identified by a tuple of two elements,
diff --git a/lib/elixir/src/elixir.erl b/lib/elixir/src/elixir.erl
index 55e7b95c7..bbd03bb9c 100644
--- a/lib/elixir/src/elixir.erl
+++ b/lib/elixir/src/elixir.erl
@@ -170,11 +170,22 @@ env_for_eval(#{lexical_tracker := Pid} = Env) ->
     versioned_vars := #{}
   },
 
-  case is_pid(Pid) andalso is_process_alive(Pid) of
-    true -> NewEnv;
-    false -> NewEnv#{lexical_tracker := nil, tracers := []}
+  case is_pid(Pid) of
+    true ->
+      case is_process_alive(Pid) of
+        true ->
+          NewEnv;
+        false ->
+          'Elixir.IO':warn(
+            <<"an __ENV__ with outdated compilation information was given to eval, "
+              "call Macro.Env.prune_compile_info/1 to prune it">>
+          ),
+          NewEnv#{lexical_tracker := nil, tracers := []}
+      end;
+    false ->
+      NewEnv#{tracers := []}
   end;
-%% TODO: Deprecate all options except line and file.
+%% TODO: Deprecate all options except line and file on v1.15.
 env_for_eval(Opts) when is_list(Opts) ->
   Env = elixir_env:new(),
 
diff --git a/lib/elixir/test/elixir/code_test.exs b/lib/elixir/test/elixir/code_test.exs
index 997fc5d5c..958a3e4e3 100644
--- a/lib/elixir/test/elixir/code_test.exs
+++ b/lib/elixir/test/elixir/code_test.exs
@@ -88,6 +88,16 @@ defmodule CodeTest do
                    ~r"argument error while evaluating example.ex between lines 1 and 2",
                    fn -> Code.eval_string("a <>\nb", [a: :a, b: :b], file: "example.ex") end
     end
+
+    test "warns when lexical tracker process is dead" do
+      {pid, ref} = spawn_monitor(fn -> :ok end)
+      assert_receive {:DOWN, ^ref, _, _, _}
+      env = %{__ENV__ | lexical_tracker: pid}
+
+      assert ExUnit.CaptureIO.capture_io(:stderr, fn ->
+               assert Code.eval_string("1 + 2", [], env) == {3, []}
+             end) =~ "an __ENV__ with outdated compilation information was given to eval"
+    end
   end
 
   test "eval_quoted/1" do
diff --git a/lib/elixir/test/elixir/macro_test.exs b/lib/elixir/test/elixir/macro_test.exs
index 430f81e7f..f01168ca9 100644
--- a/lib/elixir/test/elixir/macro_test.exs
+++ b/lib/elixir/test/elixir/macro_test.exs
@@ -791,6 +791,11 @@ defmodule MacroTest do
   describe "env" do
     doctest Macro.Env
 
+    test "prune_compile_info" do
+      assert %Macro.Env{lexical_tracker: nil, tracers: []} =
+               Macro.Env.prune_compile_info(%{__ENV__ | lexical_tracker: self(), tracers: [Foo]})
+    end
+
     test "stacktrace" do
       env = %{__ENV__ | file: "foo", line: 12}