Add label_for_completion to extension API (#10175)

This PR adds the ability for extensions to implement
`label_for_completion` to customize completions coming back from the
language server.

We've used the Gleam extension as a motivating example, adding
`label_for_completion` support to it.

Release Notes:

- N/A

---------

Co-authored-by: Max <max@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/extension_api/src/extension_api.rs

@@ -1,24 +1,69 @@
-pub use wit::*;
+use core::fmt;
+
+use wit::*;
+
+// WIT re-exports.
+//
+// We explicitly enumerate the symbols we want to re-export, as there are some
+// that we may want to shadow to provide a cleaner Rust API.
+pub use wit::{
+    current_platform, download_file, latest_github_release, make_file_executable, node_binary_path,
+    npm_install_package, npm_package_installed_version, npm_package_latest_version,
+    zed::extension::lsp, Architecture, CodeLabel, CodeLabelSpan, CodeLabelSpanLiteral, Command,
+    DownloadedFileType, EnvVars, GithubRelease, GithubReleaseAsset, GithubReleaseOptions,
+    LanguageServerInstallationStatus, Os, Range, Worktree,
+};
+
+// Undocumented WIT re-exports.
+//
+// These are symbols that need to be public for the purposes of implementing
+// the extension host, but aren't relevant to extension authors.
+#[doc(hidden)]
+pub use wit::Guest;
+
+/// A result returned from a Zed extension.
 pub type Result<T, E = String> = core::result::Result<T, E>;
 
+/// Updates the installation status for the given language server.
+pub fn set_language_server_installation_status(
+    language_server_id: &LanguageServerId,
+    status: &LanguageServerInstallationStatus,
+) {
+    wit::set_language_server_installation_status(&language_server_id.0, status)
+}
+
+/// A Zed extension.
 pub trait Extension: Send + Sync {
+    /// Returns a new instance of the extension.
     fn new() -> Self
     where
         Self: Sized;
 
+    /// Returns the command used to start the language server for the specified
+    /// language.
     fn language_server_command(
         &mut self,
-        config: LanguageServerConfig,
+        language_server_id: &LanguageServerId,
         worktree: &Worktree,
     ) -> Result<Command>;
 
+    /// Returns the initialization options to pass to the specified language server.
     fn language_server_initialization_options(
         &mut self,
-        _config: LanguageServerConfig,
+        _language_server_id: &LanguageServerId,
         _worktree: &Worktree,
     ) -> Result<Option<String>> {
         Ok(None)
     }
+
+    /// Returns the label for the given completion.
+    fn label_for_completion(
+        &self,
+        _language_server_id: &LanguageServerId,
+        _completion: Completion,
+    ) -> Option<CodeLabel> {
+        None
+    }
 }
 
 #[macro_export]
@@ -53,7 +98,7 @@ pub static ZED_API_VERSION: [u8; 6] = *include_bytes!(concat!(env!("OUT_DIR"), "
 mod wit {
     wit_bindgen::generate!({
         skip: ["init-extension"],
-        path: "./wit/since_v0.0.4",
+        path: "./wit/since_v0.0.6",
     });
 }
 
@@ -63,16 +108,76 @@ struct Component;
 
 impl wit::Guest for Component {
     fn language_server_command(
-        config: wit::LanguageServerConfig,
+        language_server_id: String,
         worktree: &wit::Worktree,
     ) -> Result<wit::Command> {
-        extension().language_server_command(config, worktree)
+        let language_server_id = LanguageServerId(language_server_id);
+        extension().language_server_command(&language_server_id, worktree)
     }
 
     fn language_server_initialization_options(
-        config: LanguageServerConfig,
+        language_server_id: String,
         worktree: &Worktree,
     ) -> Result<Option<String>, String> {
-        extension().language_server_initialization_options(config, worktree)
+        let language_server_id = LanguageServerId(language_server_id);
+        extension().language_server_initialization_options(&language_server_id, worktree)
+    }
+
+    fn labels_for_completions(
+        language_server_id: String,
+        completions: Vec<Completion>,
+    ) -> Result<Vec<Option<CodeLabel>>, String> {
+        let language_server_id = LanguageServerId(language_server_id);
+        let mut labels = Vec::new();
+        for (ix, completion) in completions.into_iter().enumerate() {
+            let label = extension().label_for_completion(&language_server_id, completion);
+            if let Some(label) = label {
+                labels.resize(ix + 1, None);
+                *labels.last_mut().unwrap() = Some(label);
+            }
+        }
+        Ok(labels)
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone)]
+pub struct LanguageServerId(String);
+
+impl fmt::Display for LanguageServerId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl CodeLabelSpan {
+    /// Returns a [`CodeLabelSpan::CodeRange`].
+    pub fn code_range(range: impl Into<wit::Range>) -> Self {
+        Self::CodeRange(range.into())
+    }
+
+    /// Returns a [`CodeLabelSpan::Literal`].
+    pub fn literal(text: impl Into<String>, highlight_name: Option<String>) -> Self {
+        Self::Literal(CodeLabelSpanLiteral {
+            text: text.into(),
+            highlight_name,
+        })
+    }
+}
+
+impl From<std::ops::Range<u32>> for wit::Range {
+    fn from(value: std::ops::Range<u32>) -> Self {
+        Self {
+            start: value.start,
+            end: value.end,
+        }
+    }
+}
+
+impl From<std::ops::Range<usize>> for wit::Range {
+    fn from(value: std::ops::Range<usize>) -> Self {
+        Self {
+            start: value.start as u32,
+            end: value.end as u32,
+        }
     }
 }