[dart2wasm] Handle JS exceptions in await exprs, finally blocks

Fixes #54024.

Change-Id: I5c92f12a453a550ce76b340116f57b329ffa97f7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/335740
Reviewed-by: Jackson Gardner <jacksongardner@google.com>
Commit-Queue: Ömer Ağacan <omersa@google.com>

pkg/dart2wasm/lib/async.dart

@@ -781,23 +781,41 @@ class AsyncCodeGenerator extends CodeGenerator {
     b.return_();
     b.end(); // masterLoop
 
-    b.catch_(translator.exceptionTag);
-
     final stackTraceLocal =
         addLocal(translator.stackTraceInfo.repr.nonNullableType);
-    b.local_set(stackTraceLocal);
 
     final exceptionLocal = addLocal(translator.topInfo.nonNullableType);
+
+    void callCompleteError() {
+      b.local_get(suspendStateLocal);
+      b.struct_get(
+          asyncSuspendStateInfo.struct, FieldIndex.asyncSuspendStateCompleter);
+      b.ref_as_non_null();
+      b.local_get(exceptionLocal);
+      b.local_get(stackTraceLocal);
+      call(translator.completerCompleteError.reference);
+      b.return_();
+    }
+
+    // Handle Dart exceptions.
+    b.catch_(translator.exceptionTag);
+    b.local_set(stackTraceLocal);
     b.local_set(exceptionLocal);
+    callCompleteError();
 
-    b.local_get(suspendStateLocal);
-    b.struct_get(
-        asyncSuspendStateInfo.struct, FieldIndex.asyncSuspendStateCompleter);
-    b.ref_as_non_null();
-    b.local_get(exceptionLocal);
-    b.local_get(stackTraceLocal);
-    call(translator.completerCompleteError.reference);
-    b.return_();
+    // Handle JS exceptions.
+    b.catch_all();
+
+    // Create a generic JavaScript error.
+    call(translator.javaScriptErrorFactory.reference);
+    b.local_set(exceptionLocal);
+
+    // JS exceptions won't have a Dart stack trace, so we attach the current
+    // Dart stack trace.
+    call(translator.stackTraceCurrent.reference);
+    b.local_set(stackTraceLocal);
+
+    callCompleteError();
 
     b.end(); // end try
 

pkg/dart2wasm/lib/code_generator.dart

@@ -1293,7 +1293,7 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
     // execution after the finalizer (no throws, returns, or breaks).
     w.Label tryFinallyBlock = b.block();
 
-    // Create one block for each wrapping label
+    // Create one block for each wrapping label.
     for (final labelBlocks in breakFinalizers.values.toList().reversed) {
       labelBlocks.add(b.block());
     }
@@ -1305,29 +1305,36 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
 
     w.Label tryBlock = b.try_();
     visitStatement(node.body);
+
     final bool mustHandleReturn =
         returnFinalizers.removeLast().mustHandleReturn;
-    b.catch_(translator.exceptionTag);
 
     // `break` statements in the current finalizer and the rest will not run
-    // the current finalizer, update the `break` targets
+    // the current finalizer, update the `break` targets.
     final removedBreakTargets = <LabeledStatement, w.Label>{};
     for (final breakFinalizerEntry in breakFinalizers.entries) {
       removedBreakTargets[breakFinalizerEntry.key] =
           breakFinalizerEntry.value.removeLast();
     }
 
-    // Run finalizer on exception
+    // Handle Dart exceptions.
+    b.catch_(translator.exceptionTag);
+    visitStatement(node.finalizer);
+    b.rethrow_(tryBlock);
+
+    // Handle JS exceptions.
+    b.catch_all();
     visitStatement(node.finalizer);
     b.rethrow_(tryBlock);
-    b.end(); // end tryBlock.
 
-    // Run finalizer on normal execution (no breaks, throws, or returns)
+    b.end(); // tryBlock
+
+    // Run finalizer on normal execution (no breaks, throws, or returns).
     visitStatement(node.finalizer);
     b.br(tryFinallyBlock);
-    b.end(); // end returnFinalizerBlock.
+    b.end(); // returnFinalizerBlock
 
-    // Run finalizer on `return`
+    // Run the finalizer on `return`.
     if (mustHandleReturn) {
       visitStatement(node.finalizer);
       if (returnFinalizers.isNotEmpty) {
@@ -1341,15 +1348,14 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
       }
     }
 
-    // Generate finalizers for `break`s in the `try` block
+    // Generate finalizers for `break`s in the `try` block.
     for (final removedBreakTargetEntry in removedBreakTargets.entries) {
       b.end();
       visitStatement(node.finalizer);
       b.br(breakFinalizers[removedBreakTargetEntry.key]!.last);
     }
 
-    // Terminate `tryFinallyBlock`
-    b.end();
+    b.end(); // tryFinallyBlock
   }
 
   @override

tests/web/wasm/js_exceptions_test.dart

@@ -0,0 +1,83 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:js_interop';
+import 'dart:_wasm';
+
+import 'package:expect/expect.dart';
+
+// Catch JS exceptions in try-catch and try-finally, in sync and async
+// functions. Also in `await`.
+void main() async {
+  defineThrowJSException();
+
+  jsExceptionCatch();
+  jsExceptionFinally();
+  jsExceptionCatchAsync();
+  jsExceptionFinallyAsync();
+}
+
+@JS()
+external void eval(String code);
+
+@JS()
+external void throwJSException();
+
+bool runtimeTrue() => int.parse('1') == 1;
+
+void defineThrowJSException() {
+  eval(r'''
+      globalThis.throwJSException = function() {
+        throw "Hi from JS";
+      }
+    ''');
+}
+
+// Catch a JS exception in `catch`.
+void jsExceptionCatch() {
+  try {
+    throwJSException();
+  } catch (e) {
+    return;
+  }
+  Expect.fail("Exception not caught");
+}
+
+// Catch a JS exception in `finally`.
+void jsExceptionFinally() {
+  if (runtimeTrue()) {
+    try {
+      throwJSException();
+    } finally {
+      return;
+    }
+  }
+  Expect.fail("Exception not caught");
+}
+
+Future<void> throwJSExceptionAsync() async {
+  return throwJSException();
+}
+
+// Catch a JS exception throw by `await` in `catch`.
+Future<void> jsExceptionCatchAsync() async {
+  try {
+    await throwJSExceptionAsync();
+  } catch (e) {
+    return;
+  }
+  Expect.fail("Exception not caught");
+}
+
+// Catch a JS exception thrown by `await` in `finally`.
+Future<void> jsExceptionFinallyAsync() async {
+  if (runtimeTrue()) {
+    try {
+      await throwJSExceptionAsync();
+    } finally {
+      return;
+    }
+  }
+  Expect.fail("Exception not caught");
+}