fix(sql) Allow tauri-plugin-sql to work when Tauri is running async (tauri-apps#2038)

Author: johncarmack1984

.changes/sql-allow-blocking-without-nested-runtime.md

@@ -0,0 +1,5 @@
+---
+"sql": "patch"
+---
+
+Allow blocking on async code without creating a nested runtime.

plugins/sql/src/lib.rs

@@ -102,6 +102,15 @@ impl MigrationSource<'static> for MigrationList {
     }
 }
 
+/// Allows blocking on async code without creating a nested runtime.
+fn run_async_command<F: std::future::Future>(cmd: F) -> F::Output {
+    if tokio::runtime::Handle::try_current().is_ok() {
+        tokio::task::block_in_place(|| tokio::runtime::Handle::current().block_on(cmd))
+    } else {
+        tauri::async_runtime::block_on(cmd)
+    }
+}
+
 /// Tauri SQL plugin builder.
 #[derive(Default)]
 pub struct Builder {
@@ -136,7 +145,7 @@ impl Builder {
             .setup(|app, api| {
                 let config = api.config().clone().unwrap_or_default();
 
-                tauri::async_runtime::block_on(async move {
+                run_async_command(async move {
                     let instances = DbInstances::default();
                     let mut lock = instances.0.write().await;
 
@@ -164,7 +173,7 @@ impl Builder {
             })
             .on_event(|app, event| {
                 if let RunEvent::Exit = event {
-                    tauri::async_runtime::block_on(async move {
+                    run_async_command(async move {
                         let instances = &*app.state::<DbInstances>();
                         let instances = instances.0.read().await;
                         for value in instances.values() {