add additional comments

src/rebar_app_discover.erl

@@ -153,6 +153,8 @@ dedup([A]) -> [A];
 dedup([H,H|T]) -> dedup([H|T]);
 dedup([H|T]) -> [H|dedup(T)].
 
+%% Read in and parse the .app file if it is availabe. Do the same for
+%% the .app.src file if it exists.
 try_handle_app_file([], AppDir, AppSrcFile, Validate) ->
     try_handle_app_src_file([], AppDir, AppSrcFile, Validate);
 try_handle_app_file([File], AppDir, AppSrcFile, Validate) ->
@@ -193,6 +195,7 @@ try_handle_app_file([File], AppDir, AppSrcFile, Validate) ->
 try_handle_app_file(Other, _AppDir, _AppSrcFile, _Validate) ->
     throw({error, {multiple_app_files, Other}}).
 
+%% Read in the .app.src file if we aren't looking for a valid (already built) app
 try_handle_app_src_file(_, _AppDir, [], _Validate) ->
     false;
 try_handle_app_src_file(_, _AppDir, _AppSrcFile, valid) ->

src/rebar_digraph.erl

@@ -124,6 +124,9 @@ find_app_by_name(Name, Apps) ->
                           rebar_app_info:name(App) =:= Name
                   end, Apps).
 
+%% The union of all entries in the applications list for an app and
+%% the deps listed in its rebar.config is all deps that may be needed
+%% for building the app.
 all_apps_deps(App) ->
     Applications = lists:usort([atom_to_binary(X, utf8) || X <- rebar_app_info:applications(App)]),
     Deps = lists:usort(lists:map(fun({Name, _}) -> Name; (Name) -> Name end, rebar_app_info:deps(App))),

src/rebar_prv_install_deps.erl

@@ -575,6 +575,9 @@ fetch_app(AppInfo, AppDir, State) ->
             throw(Error)
     end.
 
+%% This is called after the dep has been downloaded and unpacked, if it hadn't been already.
+%% So this is the first time for newly downloaded apps that its .app/.app.src data can
+%% be read in an parsed.
 update_app_info(AppDir, AppInfo) ->
     {ok, Found} = rebar_app_info:discover(AppDir),
     AppDetails = rebar_app_info:app_details(Found),