gpui: Improve Global ergonomics (#11923)

This PR adds some ergonomic improvements when working with GPUI
`Global`s.

Two new traits have been added—`ReadGlobal` and `UpdateGlobal`—that
provide associated functions on any type that implements `Global` for
accessing and updating the global without needing to call the methods on
the `cx` directly (which generally involves qualifying the type).

I looked into adding `ObserveGlobal` as well, but this seems a bit
trickier to implement as the signatures of `cx.observe_global` vary
slightly between the different contexts.

Release Notes:

- N/A

crates/assistant2/src/assistant2.rs

@@ -24,7 +24,7 @@ use fs::Fs;
 use futures::{future::join_all, StreamExt};
 use gpui::{
     list, AnyElement, AppContext, AsyncWindowContext, ClickEvent, EventEmitter, FocusHandle,
-    FocusableView, ListAlignment, ListState, Model, Render, Task, View, WeakView,
+    FocusableView, ListAlignment, ListState, Model, ReadGlobal, Render, Task, View, WeakView,
 };
 use language::{language_settings::SoftWrap, LanguageRegistry};
 use markdown::{Markdown, MarkdownStyle};
@@ -288,7 +288,7 @@ impl AssistantChat {
         workspace: WeakView<Workspace>,
         cx: &mut ViewContext<Self>,
     ) -> Self {
-        let model = CompletionProvider::get(cx).default_model();
+        let model = CompletionProvider::global(cx).default_model();
         let view = cx.view().downgrade();
         let list_state = ListState::new(
             0,
@@ -550,7 +550,7 @@ impl AssistantChat {
                 let messages = messages.await?;
 
                 let completion = cx.update(|cx| {
-                    CompletionProvider::get(cx).complete(
+                    CompletionProvider::global(cx).complete(
                         model_name,
                         messages,
                         Vec::new(),

crates/assistant2/src/completion_provider.rs

@@ -2,7 +2,7 @@ use anyhow::Result;
 use assistant_tooling::ToolFunctionDefinition;
 use client::{proto, Client};
 use futures::{future::BoxFuture, stream::BoxStream, FutureExt, StreamExt};
-use gpui::{AppContext, Global};
+use gpui::Global;
 use std::sync::Arc;
 
 pub use open_ai::RequestMessage as CompletionMessage;
@@ -11,10 +11,6 @@ pub use open_ai::RequestMessage as CompletionMessage;
 pub struct CompletionProvider(Arc<dyn CompletionProviderBackend>);
 
 impl CompletionProvider {
-    pub fn get(cx: &AppContext) -> &Self {
-        cx.global::<CompletionProvider>()
-    }
-
     pub fn new(backend: impl CompletionProviderBackend) -> Self {
         Self(Arc::new(backend))
     }

crates/assistant2/src/ui/composer.rs

@@ -3,7 +3,7 @@ use crate::{
     AssistantChat, CompletionProvider,
 };
 use editor::{Editor, EditorElement, EditorStyle};
-use gpui::{AnyElement, FontStyle, FontWeight, TextStyle, View, WeakView, WhiteSpace};
+use gpui::{AnyElement, FontStyle, FontWeight, ReadGlobal, TextStyle, View, WeakView, WhiteSpace};
 use settings::Settings;
 use theme::ThemeSettings;
 use ui::{popover_menu, prelude::*, ButtonLike, ContextMenu, Divider, TextSize, Tooltip};
@@ -139,7 +139,7 @@ impl RenderOnce for ModelSelector {
         popover_menu("model-switcher")
             .menu(move |cx| {
                 ContextMenu::build(cx, |mut menu, cx| {
-                    for model in CompletionProvider::get(cx).available_models() {
+                    for model in CompletionProvider::global(cx).available_models() {
                         menu = menu.custom_entry(
                             {
                                 let model = model.clone();