Emit defmodule tracing event

Author: josevalim

lib/elixir/lib/code.ex

@@ -158,6 +158,10 @@ defmodule Code do
       of keys to traverse in the application environment and `return` is either
       `{:ok, value}` or `:error`.
 
+    * `:defmodule` - (since v1.16.2) traced as soon as the definition of a module
+      starts. This is invoked early on in the module life-cycle, `Module.open?/1`
+      still returns `false` for such traces
+
     * `{:on_module, bytecode, _ignore}` - (since v1.13.0) traced whenever a module
       is defined. This is equivalent to the `@after_compile` callback and invoked
       after any `@after_compile` in the given module. The third element is currently

lib/elixir/src/elixir_module.erl

@@ -118,6 +118,7 @@ invalid_module_name(Module) ->
 compile(Line, Module, ModuleAsCharlist, Block, Vars, Prune, E) ->
   File = ?key(E, file),
   check_module_availability(Module, Line, E),
+  elixir_env:trace(defmodule, E),
 
   CompilerModules = compiler_modules(),
   {Tables, Ref} = build(Module, Line, File, E),

lib/elixir/test/elixir/kernel/tracers_test.exs

@@ -201,6 +201,19 @@ defmodule Kernel.TracersTest do
     end
     """)
 
+    assert_receive {:defmodule, %{module: Sample, function: nil}}
+    assert_receive {{:on_module, <<_::binary>>, :none}, %{module: Sample, function: nil}}
+  after
+    :code.purge(Sample)
+    :code.delete(Sample)
+  end
+
+  test "traces dynamic modules" do
+    compile_string("""
+    Module.create(Sample, :ok, __ENV__)
+    """)
+
+    assert_receive {:defmodule, %{module: Sample, function: nil}}
     assert_receive {{:on_module, <<_::binary>>, :none}, %{module: Sample, function: nil}}
   after
     :code.purge(Sample)