Add on_mount examples to Gettext docs (#2007)

* add `on_mount` locale examples to docs

* replace `<%= web_namespace %>` with `MyAppWeb` in doc examples

* add fallback case for logged out routes

guides/introduction/installation.md

@@ -246,7 +246,7 @@ The change is to define the `live_view` and `live_component` functions in your `
     quote do
       use Phoenix.View,
         root: "lib/<%= lib_web_name %>/templates",
-        namespace: <%= web_namespace %>
+        namespace: MyAppWeb
 
       # Import convenience functions from controllers
       import Phoenix.Controller,
@@ -260,7 +260,7 @@ The change is to define the `live_view` and `live_component` functions in your `
   def live_view do
     quote do
       use Phoenix.LiveView,
-        layout: {<%= web_namespace %>.LayoutView, "live.html"}
+        layout: {MyAppWeb.LayoutView, "live.html"}
 
       unquote(view_helpers())
     end
@@ -296,7 +296,7 @@ Note that LiveViews are automatically configured to use a "live.html.heex" layou
 
 ```elixir
 use Phoenix.LiveView,
-  layout: {<%= web_namespace %>.LayoutView, "live.html"}
+  layout: {MyAppWeb.LayoutView, "live.html"}
 ```
 
 "layouts/root.html.heex" is shared by regular and live views, "app.html.heex" is rendered inside the root layout for regular views, and "live.html.heex" is rendered inside the root layout for LiveViews. "live.html.heex" typically starts out as a copy of "app.html.heex", but using the `@socket` assign instead of `@conn`. Check the [Live Layouts](live-layouts.md) guide for more information.

guides/server/security-model.md

@@ -99,7 +99,7 @@ to run it on all LiveViews by default:
     def live_view do
       quote do
         use Phoenix.LiveView,
-          layout: {<%= web_namespace %>.LayoutView, "live.html"}
+          layout: {MyAppWeb.LayoutView, "live.html"}
 
         on_mount MyAppWeb.UserLiveAuth
         unquote(view_helpers())

guides/server/using-gettext.md

@@ -20,3 +20,31 @@ Then in your LiveView `mount/3`, you can restore the locale:
       Gettext.put_locale(MyApp.Gettext, locale)
       {:ok, socket}
     end
+
+You can also use the `on_mount` (`Phoenix.LiveView.on_mount/1`) hook to
+automatically restore the locale for every LiveView in your application:
+
+    defmodule MyAppWeb.RestoreLocale do
+      import Phoenix.LiveView
+
+      def on_mount(:default, _params, %{"locale" => locale} = _session, socket) do
+        Gettext.put_locale(MyApp.Gettext, locale)
+        {:cont, socket}
+      end
+
+      # for any logged out routes
+      def on_mount(:default, _params, _session, socket), do: {:cont, socket}
+    end
+
+Then, add this hook to `def live_view` under `MyAppWeb`, to run it on all
+LiveViews by default:
+
+    def live_view do
+      quote do
+        use Phoenix.LiveView,
+          layout: {MyAppWeb.LayoutView, "live.html"}
+
+        on_mount MyAppWeb.RestoreLocale
+        unquote(view_helpers())
+      end
+    end