Add Kernel.dbg/0 which debugs binding/0 (#12009)

lib/elixir/lib/kernel.ex

@@ -5806,6 +5806,8 @@ defmodule Kernel do
       |> String.split() #=> ["Elixir", "is", "cool"]
       |> List.first() #=> "Elixir"
 
+  With no arguments, `dbg()` debugs information about the current binding. See `binding/1`.
+
   ## Configuring the debug function
 
   One of the benefits of `dbg/2` is that its debugging logic is configurable,
@@ -5846,7 +5848,7 @@ defmodule Kernel do
   are inspected. They are the same options accepted by `inspect/2`.
   """
   @doc since: "1.14.0"
-  defmacro dbg(code, options \\ []) do
+  defmacro dbg(code \\ quote(do: binding()), options \\ []) do
     {mod, fun, args} = Application.compile_env!(__CALLER__, :elixir, :dbg_callback)
     apply(mod, fun, [code, options, __CALLER__ | args])
   end

lib/elixir/test/elixir/kernel_test.exs

@@ -1480,5 +1480,16 @@ defmodule KernelTest do
       assert output =~ "[:foo, :foo, :foo]"
       refute output =~ "\\e["
     end
+
+    test "prints binding() if no arguments are given" do
+      my_var = 1
+      my_other_var = :foo
+
+      output = capture_io(fn -> dbg() end)
+
+      assert output =~ "binding()"
+      assert output =~ "my_var:"
+      assert output =~ "my_other_var:"
+    end
   end
 end