Plugin templates enabled

This lets a plugin define templates to be loaded:

    $ rebar3 new
    ...
    proper (plugin): A basic PropEr suite for an OTP application
    ...
    $ rebar3 new help proper
    proper:
            plugin template (...)
            Description: A basic PropEr suite for an OTP application
            Variables:
                    name="suite" (...)
                    ...
    → rebar3 new proper fakesuite
    ===> Writing test/prop_fakesuite.erl

In this case, proper is a fake template file I've put by hand in
_build/default/plugins/rebar3_proper/priv/<somename>/, meaning it will
only work as far as it's called from the project's root.

The priority order of plugins is now .config > plugin > built-in, such
that someone could ensure plugins do not crush their own private
templates, but also that custom or plugin templates do overtake built-in
ones. It used to be Built-in > .config only.

Templates are searched for recursively in the priv/ directory of
plugins.

3 files changed, 35 insertions, 7 deletions

diff --git a/src/rebar_app_info.erl b/src/rebar_app_info.erl
index 95b4624..9fee4e0 100644
--- a/src/rebar_app_info.erl
+++ b/src/rebar_app_info.erl
@@ -23,6 +23,7 @@
          original_vsn/1,
          original_vsn/2,
          ebin_dir/1,
+         priv_dir/1,
          applications/1,
          applications/2,
          profiles/1,
@@ -361,6 +362,10 @@ out_dir(AppInfo=#app_info_t{}, OutDir) ->
 ebin_dir(#app_info_t{out_dir=OutDir}) ->
     ec_cnv:to_list(filename:join(OutDir, "ebin")).
 
+-spec priv_dir(t()) -> file:name().
+priv_dir(#app_info_t{out_dir=OutDir}) ->
+    ec_cnv:to_list(filename:join(OutDir, "priv")).
+
 -spec resource_type(t(), pkg | src) -> t().
 resource_type(AppInfo=#app_info_t{}, Type) ->
     AppInfo#app_info_t{resource_type=Type}.
diff --git a/src/rebar_prv_new.erl b/src/rebar_prv_new.erl
index 71560d5..064315e 100644
--- a/src/rebar_prv_new.erl
+++ b/src/rebar_prv_new.erl
@@ -132,10 +132,13 @@ show_template({Name, Type, Location, Description, Vars}) ->
                format_vars(Vars)]).
 
 format_type(escript) -> "built-in";
+format_type(plugin) -> "plugin";
 format_type(file) -> "custom".
 
 format_type(escript, _) ->
     "built-in template";
+format_type(plugin, Loc) ->
+    io_lib:format("plugin template (~s)", [Loc]);
 format_type(file, Loc) ->
     io_lib:format("custom template (~s)", [Loc]).
 
diff --git a/src/rebar_templater.erl b/src/rebar_templater.erl
index f0b2ce8..f687637 100644
--- a/src/rebar_templater.erl
+++ b/src/rebar_templater.erl
@@ -239,6 +239,7 @@ replace_var([H|T], Acc, Vars) ->
 %% Load a list of all the files in the escript and on disk
 find_templates(State) ->
     DiskTemplates = find_disk_templates(State),
+    PluginTemplates = find_plugin_templates(State),
     {MainTemplates, Files} =
         case rebar_state:escript_path(State) of
             undefined ->
@@ -249,19 +250,23 @@ find_templates(State) ->
                 F = cache_escript_files(State),
                 {find_escript_templates(F), F}
         end,
-    AvailTemplates = find_available_templates(DiskTemplates,
-                                              MainTemplates),
+    AvailTemplates = find_available_templates([MainTemplates,
+                                               PluginTemplates,
+                                               DiskTemplates]),
     ?DEBUG("Available templates: ~p\n", [AvailTemplates]),
     {AvailTemplates, Files}.
 
-find_available_templates(TemplateList1, TemplateList2) ->
-    AvailTemplates = prioritize_templates(
-                       tag_names(TemplateList1),
-                       tag_names(TemplateList2)),
-
+find_available_templates(TemplateListList) ->
+    AvailTemplates = prioritize_templates(TemplateListList),
     ?DEBUG("Available templates: ~p\n", [AvailTemplates]),
     AvailTemplates.
 
+prioritize_templates([TemplateList]) ->
+    tag_names(TemplateList);
+prioritize_templates([TemplateList | TemplateListList]) ->
+    prioritize_templates(tag_names(TemplateList),
+                         prioritize_templates(TemplateListList)).
+
 %% Scan the current escript for available files
 cache_escript_files(State) ->
     {ok, Files} = rebar_utils:escript_foldl(
@@ -299,6 +304,14 @@ find_other_templates(State) ->
             rebar_utils:find_files(TemplateDir, ?TEMPLATE_RE)
     end.
 
+%% Fetch template indexes that sit on disk in plugins
+find_plugin_templates(State) ->
+    [{plugin, File}
+     || App <- rebar_state:all_plugin_deps(State),
+        Priv <- [rebar_app_info:priv_dir(App)],
+        Priv =/= undefined,
+        File <- rebar_utils:find_files(Priv, ?TEMPLATE_RE)].
+
 %% Take an existing list of templates and tag them by name the way
 %% the user would enter it from the CLI
 tag_names(List) ->
@@ -316,6 +329,10 @@ prioritize_templates([{Name, Type, File} | Rest], Valid) ->
             ?DEBUG("Skipping template ~p, due to presence of a built-in "
                    "template with the same name", [Name]),
             prioritize_templates(Rest, Valid);
+        {_, plugin, _} ->
+            ?DEBUG("Skipping template ~p, due to presence of a plugin "
+                   "template with the same name", [Name]),
+            prioritize_templates(Rest, Valid);
         {_, file, _} ->
             ?DEBUG("Skipping template ~p, due to presence of a custom "
                    "template at ~s", [Name, File]),
@@ -327,6 +344,9 @@ prioritize_templates([{Name, Type, File} | Rest], Valid) ->
 load_file(Files, escript, Name) ->
     {Name, Bin} = lists:keyfind(Name, 1, Files),
     Bin;
+load_file(_Files, plugin, Name) ->
+    {ok, Bin} = file:read_file(Name),
+    Bin;
 load_file(_Files, file, Name) ->
     {ok, Bin} = file:read_file(Name),
     Bin.