Overhaul extension registration (#21083)

This PR overhauls extension registration in order to make it more
modular.

The `extension` crate now contains an `ExtensionHostProxy` that can be
used to register various proxies that the extension host can use to
interact with the rest of the system.

There are now a number of different proxy traits representing the
various pieces of functionality that can be provided by an extension.
The respective crates that provide this functionality can implement
their corresponding proxy trait in order to register a proxy that the
extension host will use to register the bits of functionality provided
by the extension.

Release Notes:

- N/A

crates/snippet_provider/Cargo.toml

@@ -11,6 +11,7 @@ workspace = true
 [dependencies]
 anyhow.workspace = true
 collections.workspace = true
+extension.workspace = true
 fs.workspace = true
 futures.workspace = true
 gpui.workspace = true

crates/snippet_provider/src/extension_snippet.rs

@@ -0,0 +1,26 @@
+use std::path::PathBuf;
+use std::sync::Arc;
+
+use anyhow::Result;
+use extension::{ExtensionHostProxy, ExtensionSnippetProxy};
+use gpui::AppContext;
+
+use crate::SnippetRegistry;
+
+pub fn init(cx: &mut AppContext) {
+    let proxy = ExtensionHostProxy::default_global(cx);
+    proxy.register_snippet_proxy(SnippetRegistryProxy {
+        snippet_registry: SnippetRegistry::global(cx),
+    });
+}
+
+struct SnippetRegistryProxy {
+    snippet_registry: Arc<SnippetRegistry>,
+}
+
+impl ExtensionSnippetProxy for SnippetRegistryProxy {
+    fn register_snippet(&self, path: &PathBuf, snippet_contents: &str) -> Result<()> {
+        self.snippet_registry
+            .register_snippets(path, snippet_contents)
+    }
+}

crates/snippet_provider/src/lib.rs

@@ -1,3 +1,4 @@
+mod extension_snippet;
 mod format;
 mod registry;
 
@@ -18,6 +19,7 @@ use util::ResultExt;
 
 pub fn init(cx: &mut AppContext) {
     SnippetRegistry::init_global(cx);
+    extension_snippet::init(cx);
 }
 
 // Is `None` if the snippet file is global.