zed_extension_api: Return structured slash command completions (#13879)

This PR updates the extension API to use structured slash command
completions instead of plain strings.

This allows slash commands defined in extensions to take advantage of
the improvements made in #13876.

Release Notes:

- N/A

crates/extension_api/src/extension_api.rs

@@ -25,7 +25,9 @@ pub use wit::{
         npm_package_latest_version,
     },
     zed::extension::platform::{current_platform, Architecture, Os},
-    zed::extension::slash_command::{SlashCommand, SlashCommandOutput, SlashCommandOutputSection},
+    zed::extension::slash_command::{
+        SlashCommand, SlashCommandArgumentCompletion, SlashCommandOutput, SlashCommandOutputSection,
+    },
     CodeLabel, CodeLabelSpan, CodeLabelSpanLiteral, Command, DownloadedFileType, EnvVars,
     KeyValueStore, LanguageServerInstallationStatus, Range, Worktree,
 };
@@ -114,7 +116,7 @@ pub trait Extension: Send + Sync {
         &self,
         _command: SlashCommand,
         _query: String,
-    ) -> Result<Vec<String>, String> {
+    ) -> Result<Vec<SlashCommandArgumentCompletion>, String> {
         Ok(Vec::new())
     }
 
@@ -247,7 +249,7 @@ impl wit::Guest for Component {
     fn complete_slash_command_argument(
         command: SlashCommand,
         query: String,
-    ) -> Result<Vec<String>, String> {
+    ) -> Result<Vec<SlashCommandArgumentCompletion>, String> {
         extension().complete_slash_command_argument(command, query)
     }
 

crates/extension_api/wit/since_v0.0.7/extension.wit

@@ -8,7 +8,7 @@ world extension {
 
     use common.{range};
     use lsp.{completion, symbol};
-    use slash-command.{slash-command, slash-command-output};
+    use slash-command.{slash-command, slash-command-argument-completion, slash-command-output};
 
     /// Initializes the extension.
     export init-extension: func();
@@ -130,7 +130,7 @@ world extension {
     export labels-for-symbols: func(language-server-id: string, symbols: list<symbol>) -> result<list<option<code-label>>, string>;
 
     /// Returns the completions that should be shown when completing the provided slash command with the given query.
-    export complete-slash-command-argument: func(command: slash-command, query: string) -> result<list<string>, string>;
+    export complete-slash-command-argument: func(command: slash-command, query: string) -> result<list<slash-command-argument-completion>, string>;
 
     /// Returns the output from running the provided slash command.
     export run-slash-command: func(command: slash-command, argument: option<string>, worktree: borrow<worktree>) -> result<slash-command-output, string>;

crates/extension_api/wit/since_v0.0.7/slash-command.wit

@@ -28,4 +28,14 @@ interface slash-command {
         /// The label to display in the placeholder for this section.
         label: string,
     }
+
+    /// A completion for a slash command argument.
+    record slash-command-argument-completion {
+        /// The label to display for this completion.
+        label: string,
+        /// The new text that should be inserted into the command when this completion is accepted.
+        new-text: string,
+        /// Whether the command should be run when accepting this completion.
+        run-command: bool,
+    }
 }