Add tests for allow_locals option

lib/elixir/lib/macro/env.ex

@@ -558,13 +558,13 @@ defmodule Macro.Env do
 
     * `:allow_locals` - controls how local macros are resolved.
       Defaults to `true`.
-      
+
       - When `false`, does not attempt to capture local macros defined in the
         current module in `env`
       - When `true`, uses a default resolver that looks for public macros in
         the current module
-      - When a function, uses the function as a custom local resolver. The function
-        must have the signature: `(meta, name, arity, env) -> function() | false`
+      - When a function, it will be invoked to lazily compute a local function
+        (or return false). It has signature `(-> function() | false)`
 
     * `:check_deprecations` - when set to `false`, does not check for deprecations
       when expanding macros
@@ -591,7 +591,7 @@ defmodule Macro.Env do
         # When allow_locals is a callback, we don't need to pass module macros as extra
         # because the callback will handle local macro resolution
         extra =
-          if is_function(allow_locals, 4) do
+          if is_function(allow_locals, 0) do
             []
           else
             case allow_locals and function_exported?(module, :__info__, 1) do

lib/elixir/src/elixir_dispatch.erl

@@ -175,9 +175,7 @@ expand_import(Meta, Name, Arity, E, Extra, AllowLocals, Trace) ->
       Local = case AllowLocals of
         false -> false;
         true  -> elixir_def:local_for(Meta, Name, Arity, [defmacro, defmacrop], E);
-        Fun when is_function(Fun, 4) ->
-          %% If we have a custom local resolver, use it.
-          Fun(Meta, Name, Arity, E)
+        Fun when is_function(Fun, 0) -> Fun()
       end,
 
       case Dispatch of

lib/elixir/test/elixir/macro/env_test.exs

@@ -207,6 +207,25 @@ defmodule Macro.EnvTest do
       assert fun.([generated: true], [quote(do: hello())]) == quote(generated: true, do: hello())
     end
 
+    defmacro allow_locals_example, do: :ok
+
+    test "allow_locals" do
+      {:macro, Macro.EnvTest, fun} =
+        expand_import(env(), meta(), :allow_locals_example, 0)
+
+      assert fun.([], []) == :ok
+
+      assert expand_import(env(), meta(), :allow_locals_example, 0, allow_locals: false) ==
+               {:error, :not_found}
+
+      assert expand_import(env(), meta(), :allow_locals_example, 0,
+               allow_locals: fn -> send(self(), false) end
+             ) ==
+               {:error, :not_found}
+
+      assert_received false
+    end
+
     test "with tracing and deprecations" do
       message = "MacroEnvMacros.my_deprecated_macro/1 is deprecated"