Fix expand crash on invalid multialias root (#14698)

Author: lukaszsamson

lib/elixir/src/elixir_expand.erl

@@ -573,18 +573,24 @@ escape_map(Map) -> {'%{}', [], lists:sort(maps:to_list(Map))}.
 expand_multi_alias_call(Kind, Meta, Base, Refs, Opts, S, E) ->
   {BaseRef, SB, EB} = expand_without_aliases_report(Base, S, E),
 
-  Fun = fun
-    ({'__aliases__', _, Ref}, SR, ER) ->
-      expand({Kind, Meta, [elixir_aliases:concat([BaseRef | Ref]), Opts]}, SR, ER);
+  case is_atom(BaseRef) of
+    true ->
+      Fun = fun
+        ({'__aliases__', _, Ref}, SR, ER) ->
+          expand({Kind, Meta, [elixir_aliases:concat([BaseRef | Ref]), Opts]}, SR, ER);
 
-    (Ref, SR, ER) when is_atom(Ref) ->
-      expand({Kind, Meta, [elixir_aliases:concat([BaseRef, Ref]), Opts]}, SR, ER);
+        (Ref, SR, ER) when is_atom(Ref) ->
+          expand({Kind, Meta, [elixir_aliases:concat([BaseRef, Ref]), Opts]}, SR, ER);
 
-    (Other, _SR, _ER) ->
-      file_error(Meta, E, ?MODULE, {expected_compile_time_module, Kind, Other})
-  end,
+        (Other, _SR, _ER) ->
+          file_error(Meta, E, ?MODULE, {expected_compile_time_module, Kind, Other})
+      end,
 
-  mapfold(Fun, SB, EB, Refs).
+      mapfold(Fun, SB, EB, Refs);
+
+    false ->
+      file_error(Meta, E, ?MODULE, {invalid_alias, Base})
+  end.
 
 resolve_super(Meta, Arity, E) ->
   Module = assert_module_scope(Meta, super, E),

lib/elixir/test/elixir/kernel/expansion_test.exs

@@ -118,6 +118,12 @@ defmodule Kernel.ExpansionTest do
       end)
     end
 
+    test "raises on multi-alias with non-atom base" do
+      assert_compile_error(~r"invalid alias: \"foo\"", fn ->
+        expand(quote(do: alias(foo.{Bar, Baz})))
+      end)
+    end
+
     test "invalid options" do
       assert_compile_error(~r"unsupported option :ops given to alias", fn ->
         expand(quote(do: alias(Foo, ops: 1)))