Fix struct/0 typespec

Closes #4915.

Signed-off-by: José Valim <[email protected]>

Author: ericmj

lib/elixir/rebar.config

@@ -1,23 +1,24 @@
 {erl_opts, [
-            warn_unused_vars,
-            warn_export_all,
-            warn_shadow_vars,
-            warn_unused_import,
-            warn_unused_function,
-            warn_bif_clash,
-            warn_unused_record,
-            warn_deprecated_function,
-            warn_obsolete_guard,
-            strict_validation,
-            warn_exported_vars,
-            %% warn_export_vars,
-            %% warn_missing_spec,
-            %% warn_untyped_record,
-            %% warnings_as_errors,
-            debug_info
-           ]}.
+  warn_unused_vars,
+  warn_export_all,
+  warn_shadow_vars,
+  warn_unused_import,
+  warn_unused_function,
+  warn_bif_clash,
+  warn_unused_record,
+  warn_deprecated_function,
+  warn_obsolete_guard,
+  strict_validation,
+  warn_exported_vars,
+  %% warn_export_vars,
+  %% warn_missing_spec,
+  %% warn_untyped_record,
+  %% warnings_as_errors,
+  debug_info,
+  {platform_define, "^18.*", old_map_specs}
+]}.
 
 {yrl_opts, [
-            {report, true},
-            {verbose, false}
-           ]}.
+  {report, true},
+  {verbose, false}
+]}.

lib/elixir/src/elixir.erl

@@ -14,11 +14,16 @@
 -export_type([charlist/0, char_list/0, struct/0, as_boolean/1, keyword/0, keyword/1]).
 -type charlist() :: string().
 -type char_list() :: string().
--type struct() :: #{'__struct__' => atom()}.
 -type as_boolean(T) :: T.
 -type keyword() :: [{atom(), any()}].
 -type keyword(T) :: [{atom(), T}].
 
+-ifdef(old_map_specs).
+-type struct() :: #{'__struct__' => atom(), atom() => any()}.
+-else.
+-type struct() :: #{'__struct__' := atom(), atom() => any()}.
+-endif.
+
 %% OTP Application API
 
 -export([start/2, stop/1, config_change/3]).