Please OTP-18

- Can't deal with := in map type declarations
- maps:update_with didn't exist back then so we reinvent it for the few
  months until we deprecate OTP 18

bootstrap

@@ -634,6 +634,7 @@ format_error(AbsSource, Extra, {Mod, Desc}) ->
 
 additional_defines() ->
     [{d, D} || {Re, D} <- [{"^[0-9]+", namespaced_types},
+                           {"^18", no_maps_update_with},
                            {"^R1[4|5]", deprecated_crypto},
                            {"^2", unicode_str},
                            {"^(R|1|20)", fun_stacktrace},

rebar.config

@@ -30,6 +30,7 @@
                       {"rebar/priv/templates/*", "_build/default/lib/"}]}.
 
 {erl_opts, [{platform_define, "^(19|2)", rand_only},
+            {platform_define, "^18", no_maps_update_with},
             {platform_define, "^2", unicode_str},
             {platform_define, "^(2[1-9])|(20\\\\.3)", filelib_find_source},
             {platform_define, "^(R|1|20)", fun_stacktrace},

src/rebar_compiler.erl

@@ -17,11 +17,11 @@
 -type extension() :: string().
 -type out_mappings() :: [{extension(), file:filename()}].
 
--callback context(rebar_app_info:t()) -> #{src_dirs     := [file:dirname()],
-                                           include_dirs := [file:dirname()],
-                                           src_ext      := extension(),
-                                           out_mappings := out_mappings(),
-                                           dependencies_opts => term()}.
+-callback context(rebar_app_info:t()) -> #{src_dirs     => [file:dirname()], % mandatory
+                                           include_dirs => [file:dirname()], % mandatory
+                                           src_ext      => extension(),      % mandatory
+                                           out_mappings => out_mappings(),   % mandatory
+                                           dependencies_opts => term()}.     % optional
 -callback needed_files(digraph:graph(), [file:filename()], out_mappings(),
                        rebar_app_info:t()) ->
     {{[file:filename()], term()}, % ErlFirstFiles (erl_opts global priority)

src/rebar_compiler_epp.erl

@@ -15,12 +15,13 @@
       Opts :: [Opt, ...],
       Opt :: {includes, [file:filename_all()]}
            | {macros, [file:filename_all()]},
-      Attributes :: #{include := [file:filename_all()],
-                      missing_include_file := [file:filename_all()],
-                      missing_include_lib := [file:filename_all()],
-                      behaviour := [atom()],
-                      parse_transform := [atom()],
-                      is_behaviour := boolean()}.
+                      %% following are all required, OTP-18 don't like it though
+      Attributes :: #{include => [file:filename_all()],
+                      missing_include_file => [file:filename_all()],
+                      missing_include_lib => [file:filename_all()],
+                      behaviour => [atom()],
+                      parse_transform => [atom()],
+                      is_behaviour => boolean()}.
 deps(File, Opts) ->
     {EppOpts, ExtraOpts} = split_opts(Opts),
     {ok, Forms} = epp:parse_file(File, EppOpts),
@@ -90,13 +91,13 @@ handle_form({attribute, _Line, file, {Path, Ln}}, Map, Opts) ->
     %% thing.
     case filename:absname(Path) of
         Path ->
-            maps:update_with(include, fun(L) -> [Path|L] end, [Path], Map);
+            update_with(include, fun(L) -> [Path|L] end, [Path], Map);
         _ -> % argh!
             handle_form({error, {Ln, {epp, {include, file, Path}}}}, Map, Opts)
     end;
 %% Include files that EPP couldn't resolve
 handle_form({error, {_Line, epp, {include, file, Name}}}, Map, _Opts) ->
-    maps:update_with(missing_include_file, fun(L) -> [Name|L] end, [Name], Map);
+    update_with(missing_include_file, fun(L) -> [Name|L] end, [Name], Map);
 handle_form({error, {_Line, epp, {include, lib, Path}}}, Map, Opts) ->
     %% This file might still exist in the regular paths not in
     %% code:lib_dir, which depend on options we pass to this module.
@@ -107,15 +108,15 @@ handle_form({error, {_Line, epp, {include, lib, Path}}}, Map, Opts) ->
             %% file because we'd need its own compiler opts and app opts
             %% to do it safely. Tracking that file is still better
             %% than nothing though.
-            maps:update_with(include, fun(L) -> [File|L] end, [File], Map);
+            update_with(include, fun(L) -> [File|L] end, [File], Map);
         {error, not_found} ->
-            maps:update_with(missing_include_lib, fun(L) -> [Path|L] end, [Path], Map)
+            update_with(missing_include_lib, fun(L) -> [Path|L] end, [Path], Map)
     end;
 %% Behaviour implementation declaration
 handle_form({attribute, _Line, behaviour, Name}, Map, _Opts) ->
-    maps:update_with(behaviour, fun(L) -> [Name|L] end, [Name], Map);
+    update_with(behaviour, fun(L) -> [Name|L] end, [Name], Map);
 handle_form({attribute, _Line, behavior, Name}, Map, _Opts) ->
-    maps:update_with(behaviour, fun(L) -> [Name|L] end, [Name], Map);
+    update_with(behaviour, fun(L) -> [Name|L] end, [Name], Map);
 %% Extract parse transforms
 handle_form({attribute, Line, compile, Attr}, Map, _Opts) when not is_list(Attr) ->
     handle_form({attribute, Line, compile, [Attr]}, Map, _Opts);
@@ -124,7 +125,7 @@ handle_form({attribute, _Line, compile, Attrs}, Map, _Opts) ->
                 {_, {M,_}} -> M;
                 {_, M} -> M
             end || T <- proplists:lookup_all(parse_transform, Attrs)],
-    maps:update_with(parse_transform, fun(L) -> Mods++L end, Mods, Map);
+    update_with(parse_transform, fun(L) -> Mods++L end, Mods, Map);
 %% Current style behaviour specification declaration
 handle_form({attribute, _Line, callback, _}, Map, _Opts) ->
     Map#{is_behaviour => true};
@@ -162,4 +163,14 @@ find_include_lib([H|T], File) ->
         false -> find_include_lib(T, File)
     end.
 
+-ifdef(no_maps_update_with).
+update_with(Key, Fun, Default, Map) ->
+    case Map of
+        #{Key := Value} -> Map#{Key := Fun(Value)};
+        _ -> Map#{Key => Default}
+    end.
+-else.
+update_with(Key, Fun, Default, Map) ->
+    maps:update_with(Key, Fun, Default, Map).
+-endif.