From 9046d3bd912bf560bee830e43b872507c47a462b Mon Sep 17 00:00:00 2001
From: Liam Appelbe <liama@google.com>
Date: Fri, 2 Sep 2022 13:51:34 -0700
Subject: [PATCH] Throw an exception when a wasm trap is hit (#88)

* Convert wasm traps to Dart exceptions

* Fix analysis
---
 wasm/lib/src/runtime.g.dart       |  5 ++---
 wasm/lib/src/wasm_error.dart      | 11 +++++++++++
 wasm/test/test_shared.dart        |  5 +++++
 wasm/test/trap_test.dart          | 33 +++++++++++++++++++++++++++++++
 wasm/tool/runtime_template.dart.t |  5 ++---
 5 files changed, 53 insertions(+), 6 deletions(-)
 create mode 100644 wasm/test/trap_test.dart

diff --git a/wasm/lib/src/runtime.g.dart b/wasm/lib/src/runtime.g.dart
index fffb946..63a0d51 100644
--- a/wasm/lib/src/runtime.g.dart
+++ b/wasm/lib/src/runtime.g.dart
@@ -597,9 +597,8 @@ class WasmRuntime {
       calloc.free(trapMessage);
       final entry = _traps.remove(message);
       if (entry == null) {
-        throw WasmError(
-          'This case is not (yet) supported. Please file an issue on pkg:wasm.',
-        );
+        // TODO(#87): Report a full stack trace to the user.
+        throw WasmException(message);
       }
       // ignore: only_throw_errors
       throw entry.exception;
diff --git a/wasm/lib/src/wasm_error.dart b/wasm/lib/src/wasm_error.dart
index f326aff..1a9e558 100644
--- a/wasm/lib/src/wasm_error.dart
+++ b/wasm/lib/src/wasm_error.dart
@@ -12,3 +12,14 @@ class WasmError extends Error {
   @override
   String toString() => 'WasmError: $message';
 }
+
+/// Exception that wraps exceptions (traps) thrown inside wasm code.
+class WasmException implements Exception {
+  /// Describes the nature of the exception.
+  final String message;
+
+  WasmException(this.message);
+
+  @override
+  String toString() => 'WasmException: $message';
+}
diff --git a/wasm/test/test_shared.dart b/wasm/test/test_shared.dart
index 33434a1..69f0a41 100644
--- a/wasm/test/test_shared.dart
+++ b/wasm/test/test_shared.dart
@@ -8,3 +8,8 @@ import 'package:wasm/src/wasm_error.dart';
 Matcher throwsWasmError(Object messageMatcher) => throwsA(
       isA<WasmError>().having((p0) => p0.message, 'message', messageMatcher),
     );
+
+Matcher throwsWasmException(Object messageMatcher) => throwsA(
+      isA<WasmException>()
+          .having((p0) => p0.message, 'message', messageMatcher),
+    );
diff --git a/wasm/test/trap_test.dart b/wasm/test/trap_test.dart
new file mode 100644
index 0000000..26a5246
--- /dev/null
+++ b/wasm/test/trap_test.dart
@@ -0,0 +1,33 @@
+// Copyright (c) 2022, 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.
+
+// Test that we can load a wasm module, find a function, and call it.
+import 'dart:typed_data';
+
+import 'package:test/test.dart';
+import 'package:wasm/wasm.dart';
+
+import 'test_shared.dart';
+
+void main() {
+  test('basics', () {
+    // (func $foo (export "foo") (type $t0) (unreachable))
+    final data = Uint8List.fromList([
+      0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x04, 0x01, 0x60, //
+      0x00, 0x00, 0x03, 0x02, 0x01, 0x00, 0x04, 0x05, 0x01, 0x70, 0x01, 0x07,
+      0x07, 0x05, 0x03, 0x01, 0x00, 0x11, 0x07, 0x10, 0x02, 0x03, 0x66, 0x6f,
+      0x6f, 0x00, 0x00, 0x06, 0x6d, 0x65, 0x6d, 0x6f, 0x72, 0x79, 0x02, 0x00,
+      0x0a, 0x05, 0x01, 0x03, 0x00, 0x00, 0x0b, 0x00, 0x2b, 0x04, 0x6e, 0x61,
+      0x6d, 0x65, 0x01, 0x06, 0x01, 0x00, 0x03, 0x66, 0x6f, 0x6f, 0x02, 0x03,
+      0x01, 0x00, 0x00, 0x04, 0x05, 0x01, 0x00, 0x02, 0x74, 0x30, 0x05, 0x05,
+      0x01, 0x00, 0x02, 0x54, 0x30, 0x06, 0x09, 0x01, 0x00, 0x06, 0x6d, 0x65,
+      0x6d, 0x6f, 0x72, 0x79,
+    ]);
+
+    final inst = WasmModule(data).builder().build();
+    final foo = inst.lookupFunction('foo');
+    // ignore: unnecessary_lambdas
+    expect(() => foo(), throwsWasmException('unreachable'));
+  });
+}
diff --git a/wasm/tool/runtime_template.dart.t b/wasm/tool/runtime_template.dart.t
index cc295a9..0faac1f 100644
--- a/wasm/tool/runtime_template.dart.t
+++ b/wasm/tool/runtime_template.dart.t
@@ -118,9 +118,8 @@ class WasmRuntime {
       calloc.free(trapMessage);
       final entry = _traps.remove(message);
       if (entry == null) {
-        throw WasmError(
-          'This case is not (yet) supported. Please file an issue on pkg:wasm.',
-        );
+        // TODO(#87): Report a full stack trace to the user.
+        throw WasmException(message);
       }
       // ignore: only_throw_errors
       throw entry.exception;