Always wait for completion resolve before applying the completion edits (#18907)

After https://github.com/rust-lang/rust-analyzer/pull/18167 and certain
people who type and complete rapidly, it turned out that we have not
waited for `completionItem/resolve` to finish before applying the
completion results.

Release Notes:

- Fixed completion items applied improperly on fast typing

crates/editor/src/editor.rs

@@ -4427,16 +4427,49 @@ impl Editor {
         &mut self,
         item_ix: Option<usize>,
         intent: CompletionIntent,
-        cx: &mut ViewContext<Editor>,
-    ) -> Option<Task<std::result::Result<(), anyhow::Error>>> {
-        use language::ToOffset as _;
-
+        cx: &mut ViewContext<Self>,
+    ) -> Option<Task<anyhow::Result<()>>> {
         let completions_menu = if let ContextMenu::Completions(menu) = self.hide_context_menu(cx)? {
             menu
         } else {
             return None;
         };
 
+        let mut resolve_task_store = completions_menu
+            .selected_completion_documentation_resolve_debounce
+            .lock();
+        let selected_completion_resolve = resolve_task_store.start_now();
+        let menu_pre_resolve = self
+            .completion_documentation_pre_resolve_debounce
+            .start_now();
+        drop(resolve_task_store);
+
+        Some(cx.spawn(|editor, mut cx| async move {
+            match (selected_completion_resolve, menu_pre_resolve) {
+                (None, None) => {}
+                (Some(resolve), None) | (None, Some(resolve)) => resolve.await,
+                (Some(resolve_1), Some(resolve_2)) => {
+                    futures::join!(resolve_1, resolve_2);
+                }
+            }
+            if let Some(apply_edits_task) = editor.update(&mut cx, |editor, cx| {
+                editor.apply_resolved_completion(completions_menu, item_ix, intent, cx)
+            })? {
+                apply_edits_task.await?;
+            }
+            Ok(())
+        }))
+    }
+
+    fn apply_resolved_completion(
+        &mut self,
+        completions_menu: CompletionsMenu,
+        item_ix: Option<usize>,
+        intent: CompletionIntent,
+        cx: &mut ViewContext<'_, Editor>,
+    ) -> Option<Task<anyhow::Result<Option<language::Transaction>>>> {
+        use language::ToOffset as _;
+
         let mat = completions_menu
             .matches
             .get(item_ix.unwrap_or(completions_menu.selected_item))?;
@@ -4595,11 +4628,7 @@ impl Editor {
             // so we should automatically call signature_help
             self.show_signature_help(&ShowSignatureHelp, cx);
         }
-
-        Some(cx.foreground_executor().spawn(async move {
-            apply_edits.await?;
-            Ok(())
-        }))
+        Some(apply_edits)
     }
 
     pub fn toggle_code_actions(&mut self, action: &ToggleCodeActions, cx: &mut ViewContext<Self>) {