Provide alias sensitive completion to special forms

lib/iex/lib/iex/autocomplete.ex

@@ -18,6 +18,9 @@ defmodule IEx.Autocomplete do
     %{kind: :variable, name: "utf32"}
   ]
 
+  @alias_only_atoms ~w(alias import require)a
+  @alias_only_charlists ~w(alias import require)c
+
   @doc """
   Provides one helper function that is injected into connecting
   remote nodes to properly handle autocompletion.
@@ -62,7 +65,11 @@ defmodule IEx.Autocomplete do
         expand_typespecs(expansion, shell, &get_module_types/1)
 
       {:dot, path, hint} ->
-        expand_dot(path, List.to_string(hint), false, shell)
+        if alias = alias_only(path, hint, code, shell) do
+          expand_aliases(List.to_string(alias), shell)
+        else
+          expand_dot(path, List.to_string(hint), false, shell)
+        end
 
       {:dot_arity, path, hint} ->
         expand_dot(path, List.to_string(hint), true, shell)
@@ -80,6 +87,9 @@ defmodule IEx.Autocomplete do
       {:local_arity, local} ->
         expand_local(List.to_string(local), true, shell)
 
+      {:local_call, local} when local in @alias_only_charlists ->
+        expand_aliases("", shell)
+
       {:local_call, local} ->
         expand_local_call(List.to_atom(local), shell)
 
@@ -382,6 +392,9 @@ defmodule IEx.Autocomplete do
           [cursor, pairs, {:|, _, [{variable, _, nil} | _]}, {:%{}, _, _} | _] ->
             container_context_map(cursor, pairs, variable, shell)
 
+          [cursor, {special_form, _, [cursor]} | _] when special_form in @alias_only_atoms ->
+            :alias_only
+
           [cursor | tail] ->
             case remove_operators(tail, cursor) do
               [{:"::", _, [_, _]}, {:<<>>, _, [_ | _]} | _] -> :bitstring_modifier
@@ -425,6 +438,16 @@ defmodule IEx.Autocomplete do
 
   ## Aliases and modules
 
+  defp alias_only(path, hint, code, shell) do
+    with {:alias, alias} <- path,
+         [] <- hint,
+         :alias_only <- container_context(code, shell) do
+      alias ++ [?.]
+    else
+      _ -> nil
+    end
+  end
+
   defp expand_aliases(all, shell) do
     case String.split(all, ".") do
       [hint] ->

lib/iex/test/iex/autocomplete_test.exs

@@ -470,6 +470,14 @@ defmodule IEx.AutocompleteTest do
     assert ~c"size/1" in entries
   end
 
+  test "completion for aliases in special forms" do
+    assert {:yes, ~c"", entries} = expand(~c"alias ")
+    assert ~c"Atom" in entries
+    refute ~c"is_atom" in entries
+
+    assert {:yes, ~c"Range", []} = expand(~c"alias Date.")
+  end
+
   test "ignore invalid Elixir module literals" do
     defmodule(:"Elixir.IEx.AutocompleteTest.Unicodé", do: nil)
     assert expand(~c"IEx.AutocompleteTest.Unicod") == {:no, ~c"", []}