Add initial support for defining language server adapters in WebAssembly-based extensions (#8645)

This PR adds **internal** ability to run arbitrary language servers via
WebAssembly extensions. The functionality isn't exposed yet - we're just
landing this in this early state because there have been a lot of
changes to the `LspAdapter` trait, and other language server logic.

## Next steps

* Currently, wasm extensions can only define how to *install* and run a
language server, they can't yet implement the other LSP adapter methods,
such as formatting completion labels and workspace symbols.
* We don't have an automatic way to install or develop these types of
extensions
* We don't have a way to package these types of extensions in our
extensions repo, to make them available via our extensions API.
* The Rust extension API crate, `zed-extension-api` has not yet been
published to crates.io, because we still consider the API a work in
progress.

Release Notes:

- N/A

---------

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

crates/extension_api/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "zed_extension_api"
+version = "0.1.0"
+edition = "2021"
+license = "Apache-2.0"
+
+[lib]
+path = "src/extension_api.rs"
+
+[dependencies]
+wit-bindgen = "0.18"
+
+[package.metadata.component]
+target = { path = "wit" }

crates/extension_api/LICENSE-APACHE

@@ -0,0 +1 @@
+../../LICENSE-APACHE

crates/extension_api/build.rs

@@ -0,0 +1,15 @@
+fn main() {
+    let version = std::env::var("CARGO_PKG_VERSION").unwrap();
+    let out_dir = std::env::var("OUT_DIR").unwrap();
+
+    let mut parts = version.split(|c: char| !c.is_digit(10));
+    let major = parts.next().unwrap().parse::<u16>().unwrap().to_be_bytes();
+    let minor = parts.next().unwrap().parse::<u16>().unwrap().to_be_bytes();
+    let patch = parts.next().unwrap().parse::<u16>().unwrap().to_be_bytes();
+
+    std::fs::write(
+        std::path::Path::new(&out_dir).join("version_bytes"),
+        [major[0], major[1], minor[0], minor[1], patch[0], patch[1]],
+    )
+    .unwrap();
+}

crates/extension_api/src/extension_api.rs

@@ -0,0 +1,62 @@
+pub struct Guest;
+pub use wit::*;
+
+pub type Result<T, E = String> = core::result::Result<T, E>;
+
+pub trait Extension: Send + Sync {
+    fn new() -> Self
+    where
+        Self: Sized;
+
+    fn language_server_command(
+        &mut self,
+        config: wit::LanguageServerConfig,
+        worktree: &wit::Worktree,
+    ) -> Result<Command>;
+}
+
+#[macro_export]
+macro_rules! register_extension {
+    ($extension_type:ty) => {
+        #[export_name = "init-extension"]
+        pub extern "C" fn __init_extension() {
+            zed_extension_api::register_extension(|| {
+                Box::new(<$extension_type as zed_extension_api::Extension>::new())
+            });
+        }
+    };
+}
+
+#[doc(hidden)]
+pub fn register_extension(build_extension: fn() -> Box<dyn Extension>) {
+    unsafe { EXTENSION = Some((build_extension)()) }
+}
+
+fn extension() -> &'static mut dyn Extension {
+    unsafe { EXTENSION.as_deref_mut().unwrap() }
+}
+
+static mut EXTENSION: Option<Box<dyn Extension>> = None;
+
+#[cfg(target_arch = "wasm32")]
+#[link_section = "zed:api-version"]
+#[doc(hidden)]
+pub static ZED_API_VERSION: [u8; 6] = *include_bytes!(concat!(env!("OUT_DIR"), "/version_bytes"));
+
+mod wit {
+    wit_bindgen::generate!({
+        exports: { world: super::Component },
+        skip: ["init-extension"]
+    });
+}
+
+struct Component;
+
+impl wit::Guest for Component {
+    fn language_server_command(
+        config: wit::LanguageServerConfig,
+        worktree: &wit::Worktree,
+    ) -> Result<wit::Command> {
+        extension().language_server_command(config, worktree)
+    }
+}

crates/extension_api/wit/extension.wit

@@ -0,0 +1,80 @@
+package zed:extension;
+
+world extension {
+    export init-extension: func();
+
+    record github-release {
+        version: string,
+        assets: list<github-release-asset>,
+    }
+
+    record github-release-asset {
+        name: string,
+        download-url: string,
+    }
+
+    record github-release-options {
+        require-assets: bool,
+        pre-release: bool,
+    }
+
+    enum os {
+        mac,
+        linux,
+        windows,
+    }
+
+    enum architecture {
+        aarch64,
+        x86,
+        x8664,
+    }
+
+    enum downloaded-file-type {
+        gzip,
+        gzip-tar,
+        zip,
+        uncompressed,
+    }
+
+    variant language-server-installation-status {
+        checking-for-update,
+        downloaded,
+        downloading,
+        cached,
+        failed(string),
+    }
+
+    /// Gets the current operating system and architecture
+    import current-platform: func() -> tuple<os, architecture>;
+
+    /// Gets the latest version of the given NPM package.
+    import npm-package-latest-version: func(package-name: string) -> result<string, string>;
+
+    /// Gets the latest release for the given GitHub repository.
+    import latest-github-release: func(repo: string, options: github-release-options) -> result<github-release, string>;
+
+    /// Downloads a file from the given url, and saves it to the given filename within the extension's
+    /// working directory. Extracts the file according to the given file type.
+    import download-file: func(url: string, output-filename: string, file-type: downloaded-file-type) -> result<_, string>;
+
+    /// Updates the installation status for the given language server.
+    import set-language-server-installation-status: func(language-server-name: string, status: language-server-installation-status);
+
+    record command {
+        command: string,
+        args: list<string>,
+        env: list<tuple<string, string>>,
+    }
+
+    resource worktree {
+        read-text-file: func(path: string) -> result<string, string>;
+    }
+
+    record language-server-config {
+        name: string,
+        language-name: string,
+    }
+
+    export language-server-command: func(config: language-server-config, worktree: borrow<worktree>) -> result<command, string>;
+}