[cts_runner] Print uncaptured errors to stderr (#8263)

This is useful when running test snippets. Update READMEs including to
mention how to do that.

Cargo.lock

@@ -976,6 +976,7 @@ dependencies = [
  "deno_webgpu",
  "deno_webidl",
  "env_logger",
+ "tempfile",
  "termcolor",
  "tokio",
 ]
@@ -3990,6 +3991,19 @@ version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1ac9aa371f599d22256307c24a9d748c041e548cbf599f35d890f9d365361790"
 
+[[package]]
+name = "tempfile"
+version = "3.23.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2d31c77bdf42a745371d260a26ca7163f1e0924b64afa0b688e61b5a9fa02f16"
+dependencies = [
+ "fastrand",
+ "getrandom 0.3.3",
+ "once_cell",
+ "rustix 1.0.8",
+ "windows-sys 0.61.0",
+]
+
 [[package]]
 name = "termcolor"
 version = "1.4.1"

Cargo.toml

@@ -187,6 +187,7 @@ spirv = "0.3"
 static_assertions = "1.1"
 strum = { version = "0.27.1", default-features = false, features = ["derive"] }
 syn = "2.0.98"
+tempfile = "3"
 toml = "0.9.0"
 trybuild = "1"
 tracy-client = "0.18"

cts_runner/Cargo.toml

@@ -22,3 +22,6 @@ deno_webidl.workspace = true
 deno_webgpu.workspace = true
 tokio = { workspace = true, features = ["full"] }
 termcolor.workspace = true
+
+[dev-dependencies]
+tempfile.workspace = true

cts_runner/README.md

@@ -0,0 +1,17 @@
+# cts_runner
+
+This crate contains infrastructure for running the WebGPU conformance tests on
+Deno's `wgpu`-based implementation of WebGPU.
+
+Instructions for running the tests via the CTS `xtask` are in the
+[top-level README](https://github.com/gfx-rs/wgpu/blob/trunk/README.md#webgpu-conformance-test-suite).
+The file [revision.txt](./revision.txt) specifies the version of the CTS that
+will be used by default.
+
+`cts_runner` is somewhat misnamed at this point, in that it is useful for
+things other than just running the CTS:
+
+- The [tests](./tests) directory contains a few directed tests for
+  Deno's bindings to `wgpu`.
+- Standalone JavaScript snippets that use WebGPU can be run
+  with a command like: `cargo run -p cts_runner -- test.js`.

cts_runner/src/bootstrap.js

@@ -224,6 +224,25 @@ const windowOrWorkerGlobalScope = {
 
 windowOrWorkerGlobalScope.console.enumerable = false;
 
+// Print uncaptured WebGPU errors to stderr. This is useful when running
+// standalone JavaScript test snippets. It isn't needed for the CTS, because the
+// CTS uses error scopes. (The CTS also installs its own error handler with
+// `addEventListener`, so having this here may result in printing duplicate
+// errors from the CTS in some cases.) Printing uncaptured errors to stderr
+// isn't desired as built-in behavior in Deno, because the console is reserved
+// for the application.
+//
+// Note that catching an error here _does not_ result in a non-zero exit status.
+const requestDevice = webgpu.GPUAdapter.prototype.requestDevice;
+webgpu.GPUAdapter.prototype.requestDevice = function(desc) {
+    return requestDevice.call(this, desc).then((device) => {
+        device.onuncapturederror = (event) => {
+            core.print("cts_runner caught WebGPU error:" + event.error.message, true);
+        };
+        return device;
+    })
+};
+
 const mainRuntimeGlobalProperties = {
   Window: globalInterfaces.windowConstructorDescriptor,
   window: util.readOnly(globalThis),

cts_runner/tests/features.js

@@ -1,5 +0,0 @@
-const adapter = await navigator.gpu.requestAdapter();
-
-if (adapter.features.has("mappable-primary-buffers")) {
-    throw new TypeError("Adapter should not report support for wgpu native-only features");
-}

cts_runner/tests/integration.rs

@@ -3,12 +3,15 @@
 // As of June 2025, these tests are not run in CI.
 
 use std::{
-    fmt::{self, Debug, Display},
+    ffi::OsStr,
+    io::Write,
     path::PathBuf,
-    process::Command,
+    process::{Command, Output},
     str,
 };
 
+use tempfile::NamedTempFile;
+
 pub fn target_dir() -> PathBuf {
     let current_exe = std::env::current_exe().unwrap();
     let target_dir = current_exe.parent().unwrap().parent().unwrap();
@@ -24,38 +27,71 @@ pub fn cts_runner_exe_path() -> PathBuf {
     p
 }
 
-pub struct JsError;
-
-impl Display for JsError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "JavaScript test returned an error")
-    }
-}
-
-impl Debug for JsError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{self}")
-    }
-}
-
-type JsResult = Result<(), JsError>;
-
-fn exec_js_test(script: &str) -> JsResult {
-    let output = Command::new(cts_runner_exe_path())
-        .arg(script)
+fn exec_cts_runner(script_file: impl AsRef<OsStr>) -> Output {
+    Command::new(cts_runner_exe_path())
+        .arg(script_file)
         .output()
-        .unwrap();
+        .unwrap()
+}
+
+fn exec_js_file(script_file: impl AsRef<OsStr>) {
+    let output = exec_cts_runner(script_file);
     println!("{}", str::from_utf8(&output.stdout).unwrap());
     eprintln!("{}", str::from_utf8(&output.stderr).unwrap());
-    output.status.success().then_some(()).ok_or(JsError)
+    assert!(output.status.success());
+}
+
+fn check_js_stderr(script: &str, expected: &str) {
+    let mut tempfile = NamedTempFile::new().unwrap();
+    tempfile.write_all(script.as_bytes()).unwrap();
+    tempfile.flush().unwrap();
+    let output = exec_cts_runner(tempfile.path());
+    assert!(
+        output.stdout.is_empty(),
+        "unexpected output on stdout: {}",
+        str::from_utf8(&output.stdout).unwrap(),
+    );
+    assert_eq!(str::from_utf8(&output.stderr).unwrap(), expected);
+    assert!(output.status.success());
+}
+
+fn exec_js(script: &str) {
+    check_js_stderr(script, "");
 }
 
 #[test]
-fn hello_compute_example() -> JsResult {
-    exec_js_test("examples/hello-compute.js")
+fn hello_compute_example() {
+    exec_js_file("examples/hello-compute.js");
 }
 
 #[test]
-fn features() -> JsResult {
-    exec_js_test("tests/features.js")
+fn features() {
+    exec_js(
+        r#"
+        const adapter = await navigator.gpu.requestAdapter();
+
+        if (adapter.features.has("mappable-primary-buffers")) {
+            throw new TypeError("Adapter should not report support for wgpu native-only features");
+        }
+    "#,
+    );
+}
+
+#[test]
+fn uncaptured_error() {
+    check_js_stderr(
+        r#"
+            const code = `const val: u32 = 1.1;`;
+
+            const adapter = await navigator.gpu.requestAdapter();
+            const device = await adapter.requestDevice();
+            device.createShaderModule({ code })
+        "#,
+        "cts_runner caught WebGPU error:
+Shader '' parsing error: the type of `val` is expected to be `u32`, but got `{AbstractFloat}`
+  ┌─ wgsl:1:7
+  │
+1 │ const val: u32 = 1.1;
+  │       ^^^ definition of `val`\n\n",
+    );
 }

deno_webgpu/README.md

@@ -14,13 +14,15 @@ a
 [wgpu trace](https://github.com/gfx-rs/wgpu/wiki/Debugging-wgpu-Applications#tracing-infrastructure)
 to the specified directory.
 
-For testing this op crate will make use of the WebGPU conformance tests suite,
-running through our WPT runner. This will be used to validate implementation
-conformance.
+This op crate is tested primarily by running the
+[WebGPU conformance test suite](https://github.com/gpuweb/cts) using `wgpu`'s
+[`cts_runner`](https://github.com/gfx-rs/wgpu/blob/trunk/README.md#webgpu-conformance-test-suite).
+`cts_runner` also has a few
+[directed tests](https://github.com/gfx-rs/wgpu/tree/trunk/cts_runner/tests)
+to fill in missing coverage.
 
-GitHub CI doesn't run with GPUs, so testing relies on software like DX WARP &
-Vulkan lavapipe. Currently, only using DX WARP works, so tests are only run on
-Windows.
+GPU availability in GitHub CI is limited, so some configurations rely on
+software like DX WARP & Vulkan lavapipe.
 
 ## Links