luci-base, luci-lua-runtime: adjust Lua template environment

To maintain full compatibility with the old Lua runtime, templates
rendered from a menu `template()` action must implicitly inherit the
`luci.dispatcher` namespace as scope while other indirectly included
templates must not.

Fixes: #6105
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

modules/luci-base/ucode/dispatcher.uc

@@ -774,7 +774,9 @@ function render_action(fn) {
 function run_action(request_path, lang, tree, resolved, action) {
 	switch (action?.type) {
 	case 'template':
-		runtime.render(action.path, {});
+		render_action(() => {
+			runtime.call('luci.dispatcher', 'render_lua_template', action.path);
+		});
 		break;
 
 	case 'view':

modules/luci-lua-runtime/luasrc/dispatcher.lua

@@ -354,6 +354,12 @@ function invoke_form_action(model, ...)
 	_G.L.include("footer")
 end
 
+function render_lua_template(path)
+	local tpl = require "luci.template"
+
+	tpl.render(path, getfenv(1))
+end
+
 
 function call(name, ...)
 	return {

modules/luci-lua-runtime/luasrc/template.lua

@@ -121,7 +121,7 @@ context.viewns = setmetatable({
 	elseif key == "resource" then
 		return L.config.main.resourcebase
 	else
-		return rawget(tbl, key) or disp[key] or _G[key] or L[key]
+		return rawget(tbl, key) or _G[key] or L[key]
 	end
 end})