gpui: Add Global marker trait (#7095)

This should prevent a class of bugs where one queries the wrong type of
global, which results in oddities at runtime.

Release Notes:

- N/A

---------

Co-authored-by: Marshall <marshall@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/theme/src/registry.rs

@@ -6,7 +6,7 @@ use anyhow::{anyhow, Context, Result};
 use derive_more::{Deref, DerefMut};
 use fs::Fs;
 use futures::StreamExt;
-use gpui::{AppContext, AssetSource, HighlightStyle, SharedString};
+use gpui::{AppContext, AssetSource, Global, HighlightStyle, SharedString};
 use parking_lot::RwLock;
 use refineable::Refineable;
 use util::ResultExt;
@@ -32,10 +32,7 @@ pub struct ThemeMeta {
 #[derive(Default, Deref, DerefMut)]
 struct GlobalThemeRegistry(Arc<ThemeRegistry>);
 
-/// Initializes the theme registry.
-pub fn init(assets: Box<dyn AssetSource>, cx: &mut AppContext) {
-    cx.set_global(GlobalThemeRegistry(Arc::new(ThemeRegistry::new(assets))));
-}
+impl Global for GlobalThemeRegistry {}
 
 struct ThemeRegistryState {
     themes: HashMap<SharedString, Arc<Theme>>,
@@ -59,6 +56,11 @@ impl ThemeRegistry {
         cx.default_global::<GlobalThemeRegistry>().0.clone()
     }
 
+    /// Sets the global [`ThemeRegistry`].
+    pub(crate) fn set_global(assets: Box<dyn AssetSource>, cx: &mut AppContext) {
+        cx.set_global(GlobalThemeRegistry(Arc::new(ThemeRegistry::new(assets))));
+    }
+
     pub fn new(assets: Box<dyn AssetSource>) -> Self {
         let registry = Self {
             state: RwLock::new(ThemeRegistryState {

crates/theme/src/settings.rs

@@ -2,7 +2,8 @@ use crate::one_themes::one_dark;
 use crate::{SyntaxTheme, Theme, ThemeRegistry, ThemeStyleContent};
 use anyhow::Result;
 use gpui::{
-    px, AppContext, Font, FontFeatures, FontStyle, FontWeight, Pixels, Subscription, ViewContext,
+    px, AppContext, Font, FontFeatures, FontStyle, FontWeight, Global, Pixels, Subscription,
+    ViewContext,
 };
 use refineable::Refineable;
 use schemars::{
@@ -34,6 +35,8 @@ pub struct ThemeSettings {
 #[derive(Default)]
 pub(crate) struct AdjustedBufferFontSize(Pixels);
 
+impl Global for AdjustedBufferFontSize {}
+
 #[derive(Clone, Debug, Default, Serialize, Deserialize, JsonSchema)]
 pub struct ThemeSettingsContent {
     #[serde(default)]

crates/theme/src/theme.rs

@@ -60,7 +60,7 @@ pub fn init(themes_to_load: LoadThemes, cx: &mut AppContext) {
         LoadThemes::JustBase => (Box::new(()) as Box<dyn AssetSource>, false),
         LoadThemes::All(assets) => (assets, true),
     };
-    registry::init(assets, cx);
+    ThemeRegistry::set_global(assets, cx);
 
     if load_user_themes {
         ThemeRegistry::global(cx).load_bundled_themes();