lsp: Fix 'Start with Hello World!' panic in SlintPad

.clippy.toml

@@ -3,3 +3,15 @@
 
 type-complexity-threshold = 2500
 too-many-arguments-threshold = 10
+
+# `disallowed-methods` is the configuration for the `clippy::disallowed_methods`
+# lint, which is allow-by-default. Listing entries here therefore has no effect
+# in crates that don't opt into the lint. We currently enable it only in the
+# slint-lsp crate (see `#![deny(clippy::disallowed_methods)]` in `tools/lsp/main.rs`
+# and `tools/lsp/wasm_main.rs`), so the entries below are effectively scoped to
+# slint-lsp. Putting them here (rather than in `tools/lsp/clippy.toml`) avoids
+# shadowing the workspace-wide thresholds above — clippy reads exactly one
+# clippy.toml per crate, with no merging.
+disallowed-methods = [
+  { path = "tokio::task::spawn_local", reason = "Use `slint_lsp::common::spawn_local` — it routes to `wasm_bindgen_futures::spawn_local` on wasm." },
+]

.github/workflows/wasm_editor_and_interpreter.yaml

@@ -80,6 +80,14 @@ jobs:
               if: ${{ always() }}
               working-directory: tools/slintpad
               run: npx github-actions-ctrf playwright-report/ctrf-report.json
+            - name: "Upload Playwright Report"
+              if: ${{ failure() }}
+              uses: actions/upload-artifact@v7
+              with:
+                  name: slintpad-playwright-report
+                  path: |
+                      tools/slintpad/playwright-report/
+                      tools/slintpad/test-results/
             - name: "Upload slintpad Artifacts"
               uses: actions/upload-artifact@v7
               with:

tools/lsp/common.rs

@@ -27,6 +27,20 @@ pub type Result<T> = std::result::Result<T, Error>;
 #[cfg(target_arch = "wasm32")]
 use crate::wasm_prelude::*;
 
+#[allow(clippy::disallowed_methods)]
+pub fn spawn_local<F>(future: F)
+where
+    F: std::future::Future + 'static,
+    F::Output: 'static,
+{
+    #[cfg(target_arch = "wasm32")]
+    wasm_bindgen_futures::spawn_local(async move {
+        let _ = future.await;
+    });
+    #[cfg(not(target_arch = "wasm32"))]
+    tokio::task::spawn_local(future);
+}
+
 /// Use this in nodes you want the language server and preview to
 /// ignore a node for code analysis purposes.
 pub const NODE_IGNORE_COMMENT: &str = "@lsp:ignore-node";

tools/lsp/language.rs

@@ -369,7 +369,7 @@ pub fn register_request_handlers(rh: &mut RequestHandler) {
             return Ok(None::<serde_json::Value>);
         }
         if params.command.as_str() == POPULATE_COMMAND {
-            tokio::task::spawn_local(populate_command(&params.arguments, ctx)?);
+            common::spawn_local(populate_command(&params.arguments, ctx)?);
             return Ok(None::<serde_json::Value>);
         }
         Ok(None::<serde_json::Value>)

tools/lsp/main.rs

@@ -3,7 +3,7 @@
 
 #![cfg(not(target_arch = "wasm32"))]
 #![allow(clippy::await_holding_refcell_ref)]
-#![deny(clippy::print_stderr, clippy::print_stdout)]
+#![deny(clippy::print_stderr, clippy::print_stdout, clippy::disallowed_methods)]
 
 #[cfg(all(feature = "preview-engine", not(feature = "preview-builtin")))]
 compile_error!(

tools/lsp/wasm_main.rs

@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-2.0 OR LicenseRef-Slint-Software-3.0
 
 #![cfg(target_arch = "wasm32")]
-#![deny(clippy::print_stderr, clippy::print_stdout)]
+#![deny(clippy::print_stderr, clippy::print_stdout, clippy::disallowed_methods)]
 
 pub mod common;
 mod fmt;

tools/slintpad/tests/populate-command.spec.ts

@@ -0,0 +1,48 @@
+// Copyright © SixtyFPS GmbH <info@slint.dev>
+// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-2.0 OR LicenseRef-Slint-Software-3.0
+
+// Regression test for https://github.com/slint-ui/slint/issues/11416:
+// clicking the "Start with Hello World!" code lens on an empty buffer used to
+// panic the wasm LSP because the command handler called tokio::task::spawn_local
+// outside of a LocalSet.
+import { test, expect } from "@playwright/test";
+
+test("'Start with Hello World!' code lens populates the editor without panicking", async ({
+    page,
+    browserName,
+}) => {
+    // Headless Firefox on CI has no WebGL, so opening the SlintPad preview
+    // panics in internal/renderers/femtovg/opengl.rs:134 with
+    // "Cannot proceed without WebGL - aborting". That panic shows a modal
+    // dialog that intercepts our code-lens click. Skip until the preview
+    // either gets a software-WebGL fallback or stops panicking on init.
+    test.skip(browserName === "firefox", "preview panics without WebGL");
+
+    // A single-whitespace `snippet` makes SlintPad open a main.slint whose content
+    // has no non-whitespace tokens, which is the condition under which the LSP
+    // emits the "Start with Hello World!" code lens (see tools/lsp/language.rs).
+    await page.goto("http://localhost:3000/?snippet=%20");
+    await expect(page.locator("#tab-key-1-0")).toContainText("main.slint");
+
+    // Wait for the LSP-provided code lens to show up and click it. This sends
+    // `workspace/executeCommand slint/populate`, which is the path that used
+    // to panic in the wasm LSP.
+    const code_lens = page.getByRole("button", {
+        name: "Start with Hello World!",
+    });
+    await expect(code_lens).toBeVisible({ timeout: 20_000 });
+    await code_lens.click();
+
+    // Wait until the LSP has responded — either the populate edit landed, or
+    // a panic dialog popped up.
+    const editor = page.locator(".monaco-editor").first();
+    const panic_dialog = page.locator("dialog.panic_dialog");
+    const main_window = editor.getByText("MainWindow");
+    await expect(panic_dialog.or(main_window)).toBeVisible({ timeout: 15_000 });
+
+    // The critical assertion: no panic dialog. On failure the page snapshot
+    // in the error context will show the panic message from the LSP.
+    await expect(panic_dialog).toHaveCount(0);
+    // And the populate edit actually landed.
+    await expect(editor).toContainText('"Hello World!"');
+});