Add API for deleting SCM

This is used by Hex when its application is stopped
to revert its changes to Mix state.

Author: josevalim

lib/mix/lib/mix/scm.ex

@@ -131,6 +131,14 @@ defmodule Mix.SCM do
     Mix.State.get(:scm)
   end
 
+  @doc """
+  Deletes the given SCM from the list of available SCMs.
+  """
+  @doc since: "1.16.2"
+  def delete(mod) when is_atom(mod) do
+    Mix.State.update(:scm, &List.delete(&1, mod))
+  end
+
   @doc """
   Prepends the given SCM module to the list of available SCMs.
   """

lib/mix/test/mix/scm_test.exs

@@ -12,10 +12,14 @@ defmodule Mix.SCMTest do
   test "prepends an SCM" do
     Mix.SCM.prepend(Hello)
     assert Enum.at(Mix.SCM.available(), 0) == Hello
+    Mix.SCM.delete(Hello)
+    assert Hello not in Mix.SCM.available()
   end
 
   test "appends an SCM" do
     Mix.SCM.append(Hello)
     assert Enum.at(Mix.SCM.available(), -1) == Hello
+    Mix.SCM.delete(Hello)
+    assert Hello not in Mix.SCM.available()
   end
 end