PluginGroups like Bundles

rfcs/67-plugingroups-like-bundles.md

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+# Feature Name: Plugingroups like Bundles
+
+## Summary
+
+Make PluginGroups like Bundles, so they are just structs. Then the ordering will be made by a gen_graph function, maybe with the new planned `bevy_graph` (https://github.com/bevyengine/bevy/discussions/6719) ?
+This will make PluginGroups from the design consistent to the other bevy types.
+
+## Motivation
+
+First, a new possibilty: adding plugingroups inside of pluginsgroup (cool). (a guy on discord asked this https://discord.com/channels/691052431525675048/1044672077451513906) and what he wanted (adding plugingroups inside of plugingroups) just wans't possible :c.
+Every time when I see PluginGroups it makes my brain think about **Design consitency**, because most of the other bevy types are just structs with default rust constructors.
+It also bothers me when i set plugins that for example then implement `WindowPlugin::default()` only to let me use `.set(WindowPlugin { .. })` later.
+
+## Example Design Impl
+
+```rust
+#[derive(Default)]
+pub struct MyPlugins {
+  main_plugin: MainPlugin,
+  #[plugingroup]
+  other_plugin_group: OtherPlugins,
+  #[cfg(feature = "optional")]
+  optional: OptionalPlugin,
+}
+
+impl PluginGroup for MyPlugins {
+  fn gen_graph(mut self) -> PluginGraph<Self> {
+    let mut graph_builder = PluginGraph::new();
+    builder.append::<MainPlugin>();
+    builder.before::<OtherPlugins, MainPlugin>();
+    #[cfg(feature = "optional")]
+    {
+      builder.append::<OptionalPlugin>();
+    }
+    graph_builder.build(self)
+  }
+}
+
+app.add_plugins(MyPlugins {
+  main_plugin: MainPlugin { .. },
+  ..Default::default()
+}).plugin_graph().after::<OtherPlugins, MainPlugin>(); // make plugin graph editable in app, make it also change order later
+```
+
+## Final Note
+
+I'm not sure about the naming, about the RFC in general. But thats a RFC about (i think). But with your help i think this can be a well done feature :).
+
+And a thing i just saw: this will remove a functionality (which i never saw used and i am even not sure if it is even possible):
+```rust
+app.add_plugins(MyPlugins::custom_setting(CustomSetting::Minimum)); // this would for example just add Plugin x and y, with CustomSetting::Everything, it would also add Plugin z.
+// something like optional plugins via constructor isn't possible with the new design, i think.
+```
+
+So yeah, I'm looking forward to make this feature good and cool so everybody likes it (hopefully) and it can be adopted to also make it easier for the above mentioned `bevy_graph` and bevy in general.
+Maybe this could be also an addition to the new stageless design? idk, we'll see :)