Don't require repo arg for building under certain conditions (#303)

Most cases for using the build provider shouldn't require specifying a repo argument.
The exception is when there is more than one repo found and at least one has doc config set on the
repo.

In addition, configuring documentation providers within repo config is deprecated and a warning will
be emitted if such config is detected.

src/rebar3_hex.erl

@@ -7,6 +7,7 @@
         , get_required/2
         , task_args/1
         , task_state/1
+        , task_state/2
         , repo_opt/0
         , help_opt/0
         ]).
@@ -15,10 +16,10 @@
 
 -type task() :: #{raw_opts := proplists:proplist(),
                   raw_args := list(),
-                  args := map(), 
-                  repo := map(), 
-                  apps := [rebar_app_info:t()], 
-                  state := rebar_state:t(), 
+                  args := map(),
+                  repo := map(),
+                  apps := [rebar_app_info:t()],
+                  state := rebar_state:t(),
                   multi_app := boolean()
                  }.
 
@@ -71,26 +72,30 @@ task_args(State) ->
 %% as returned from rebar_state:command_parsed_args/1 as raw_args and raw_opts.
 -spec task_state(rebar_state:t()) -> {ok, task()} | {error, term()}.
 task_state(State) ->
-    {Opts0, Args0} = rebar_state:command_parsed_args(State),
      case rebar3_hex_config:repo(State) of
-         {ok, Repo} -> 
-             Opts = get_args(State),
-             CurrentTask = maps:get(task, Opts, undefined),
-             Opts1 = Opts#{task => CurrentTask},
-             case rebar_state:project_apps(State) of 
-                 [] ->
-                     {ok, #{raw_opts => Opts0, raw_args => Args0, args => Opts1, repo => Repo, state => State, multi_app => false, apps => []}};
-                 [_App] = Apps ->
-                    {ok, #{raw_opts => Opts0, raw_args => Args0, args => Opts1, repo => Repo, state => State, multi_app => false, apps => Apps}};
-                 [_|_] = Apps ->
-                    {ok, #{raw_opts => Opts0, raw_args => Args0, args => Opts1, repo => Repo, state => State, multi_app => true, apps => Apps}}
-             end;
-         Err -> 
+         {ok, Repo} ->
+             {ok, task_state(State, Repo)};
+        Err ->
             Err
      end.
 
+-spec task_state(rebar_state:t(), map()) -> task().
+task_state(State, Repo) ->
+    {Opts0, Args0} = rebar_state:command_parsed_args(State),
+    Opts = get_args(State),
+    CurrentTask = maps:get(task, Opts, undefined),
+    Opts1 = Opts#{task => CurrentTask},
+    case rebar_state:project_apps(State) of
+        [] ->
+            #{raw_opts => Opts0, raw_args => Args0, args => Opts1, repo => Repo, state => State, multi_app => false, apps => []};
+        [_App] = Apps ->
+            #{raw_opts => Opts0, raw_args => Args0, args => Opts1, repo => Repo, state => State, multi_app => false, apps => Apps};
+        [_|_] = Apps ->
+            #{raw_opts => Opts0, raw_args => Args0, args => Opts1, repo => Repo, state => State, multi_app => true, apps => Apps}
+     end.
+
 -spec get_args(rebar_state:t()) -> map().
-get_args(State) -> 
+get_args(State) ->
     {Opts, Args} = rebar_state:command_parsed_args(State),
     Opts1 = lists:foldl(fun (Arg, Acc) ->
                                 case is_atom(Arg) of
@@ -100,14 +105,14 @@ get_args(State) ->
                                         case Arg of
                                             {task, Task} ->
                                                 [{task, list_to_atom(Task)} | Acc];
-                                             _ -> 
+                                             _ ->
                                               [Arg | Acc]
                                         end
                                 end
                         end,
                         [],
                         Opts),
-    
+
     Opts2 = lists:foldl(fun (Arg, Acc) ->
                                 case is_atom(Arg) of
                                     true ->