Add Process.get_label/1 to expose :proc_lib.get_label (#15169)

Author: sabiwara

lib/elixir/lib/process.ex

@@ -979,6 +979,30 @@ defmodule Process do
   @spec unalias(alias) :: boolean
   defdelegate unalias(alias), to: :erlang
 
+  @doc """
+  Returns the label set for the process `pid` as set with `set_label/1`
+  or `:proc_lib.set_label/1`.
+
+  Defaults to the current process when `pid` is not passed.
+
+  ## Examples
+
+      Process.set_label({:any, "term"})
+      Process.get_label()
+      #=> {:any, "term"}
+
+  Returns `nil` when not set:
+
+      Process.get_label(pid)
+      #=> nil
+
+  """
+  @doc since: "1.20.0"
+  @spec get_label(pid()) :: term()
+  def get_label(pid \\ self()) do
+    nilify(:proc_lib.get_label(pid))
+  end
+
   @doc """
   Add a descriptive term to the current process.
 

lib/elixir/test/elixir/process_test.exs

@@ -180,9 +180,22 @@ defmodule ProcessTest do
     end
   end
 
-  describe "set_label/1" do
-    @compile {:no_warn_undefined, :proc_lib}
+  describe "get_label/1" do
+    test "gets a process label, compatible with `:proc_lib.set_label/1`" do
+      label = {:some_label, :rand.uniform(99999)}
+      assert :ok = :proc_lib.set_label(label)
+
+      assert Process.get_label() == label
+      assert Process.get_label(self()) == label
+    end
 
+    test "returns nil when not set" do
+      pid = spawn(fn -> :ok end)
+      assert Process.get_label(pid) == nil
+    end
+  end
+
+  describe "set_label/1" do
     test "sets a process label, compatible with `:proc_lib.get_label/1`" do
       label = {:some_label, :rand.uniform(99999)}
       assert :ok = Process.set_label(label)