LibWasm+LibWeb: Sneak a JS::Completion into Wasm::Result

Imported functions in Wasm may throw JS exceptions, and we need to
preserve these exceptions so we can pass them to the calling JS code.

This also adds a `assert_wasm_result()` API to Result for cases where
only Wasm traps or values are expected (e.g. internal uses) to avoid
making LibWasm (pointlessly) handle JS exceptions that will never show
up in reality.

Meta/Lagom/CMakeLists.txt

@@ -552,7 +552,7 @@ if (BUILD_LAGOM)
         endif()
 
         add_executable(wasm ../../Userland/Utilities/wasm.cpp)
-        target_link_libraries(wasm LibCore LibWasm LibLine LibMain)
+        target_link_libraries(wasm LibCore LibWasm LibLine LibMain LibJS)
 
         add_executable(xml ../../Userland/Utilities/xml.cpp)
         target_link_libraries(xml LibCore LibXML LibMain)

Tests/LibWasm/CMakeLists.txt

@@ -1,2 +1,2 @@
-serenity_testjs_test(test-wasm.cpp test-wasm LIBS LibWasm)
+serenity_testjs_test(test-wasm.cpp test-wasm LIBS LibWasm LibJS)
 install(TARGETS test-wasm RUNTIME DESTINATION bin OPTIONAL)

Tests/LibWasm/test-wasm.cpp

@@ -246,6 +246,9 @@ JS_DEFINE_NATIVE_FUNCTION(WebAssemblyModule::wasm_invoke)
     if (result.is_trap())
         return vm.throw_completion<JS::TypeError>(TRY_OR_THROW_OOM(vm, String::formatted("Execution trapped: {}", result.trap().reason)));
 
+    if (result.is_completion())
+        return result.completion();
+
     if (result.values().is_empty())
         return JS::js_null();
 

Userland/Libraries/LibWasm/AbstractMachine/AbstractMachine.cpp

@@ -175,7 +175,7 @@ InstantiationResult AbstractMachine::instantiate(Module const& module, Vector<Ex
                 entry.expression(),
                 1,
             });
-            auto result = config.execute(interpreter);
+            auto result = config.execute(interpreter).assert_wasm_result();
             if (result.is_trap())
                 instantiation_result = InstantiationError { DeprecatedString::formatted("Global value construction trapped: {}", result.trap().reason) };
             else
@@ -202,7 +202,7 @@ InstantiationResult AbstractMachine::instantiate(Module const& module, Vector<Ex
                     entry,
                     entry.instructions().size(),
                 });
-                auto result = config.execute(interpreter);
+                auto result = config.execute(interpreter).assert_wasm_result();
                 if (result.is_trap()) {
                     instantiation_result = InstantiationError { DeprecatedString::formatted("Element construction trapped: {}", result.trap().reason) };
                     return IterationDecision::Continue;
@@ -255,7 +255,7 @@ InstantiationResult AbstractMachine::instantiate(Module const& module, Vector<Ex
                 active_ptr->expression,
                 1,
             });
-            auto result = config.execute(interpreter);
+            auto result = config.execute(interpreter).assert_wasm_result();
             if (result.is_trap()) {
                 instantiation_result = InstantiationError { DeprecatedString::formatted("Element section initialisation trapped: {}", result.trap().reason) };
                 return IterationDecision::Break;
@@ -315,7 +315,7 @@ InstantiationResult AbstractMachine::instantiate(Module const& module, Vector<Ex
                         data.offset,
                         1,
                     });
-                    auto result = config.execute(interpreter);
+                    auto result = config.execute(interpreter).assert_wasm_result();
                     if (result.is_trap()) {
                         instantiation_result = InstantiationError { DeprecatedString::formatted("Data section initialisation trapped: {}", result.trap().reason) };
                         return;

Userland/Libraries/LibWasm/AbstractMachine/AbstractMachine.h

@@ -13,6 +13,9 @@
 #include <AK/Result.h>
 #include <LibWasm/Types.h>
 
+// NOTE: Special case for Wasm::Result.
+#include <LibJS/Runtime/Completion.h>
+
 namespace Wasm {
 
 class Configuration;
@@ -171,6 +174,35 @@ struct Trap {
     DeprecatedString reason;
 };
 
+// A variant of Result that does not include external reasons for error (JS::Completion, for now).
+class PureResult {
+public:
+    explicit PureResult(Vector<Value> values)
+        : m_result(move(values))
+    {
+    }
+
+    PureResult(Trap trap)
+        : m_result(move(trap))
+    {
+    }
+
+    auto is_trap() const { return m_result.has<Trap>(); }
+    auto& values() const { return m_result.get<Vector<Value>>(); }
+    auto& values() { return m_result.get<Vector<Value>>(); }
+    auto& trap() const { return m_result.get<Trap>(); }
+    auto& trap() { return m_result.get<Trap>(); }
+
+private:
+    friend class Result;
+    explicit PureResult(Variant<Vector<Value>, Trap>&& result)
+        : m_result(move(result))
+    {
+    }
+
+    Variant<Vector<Value>, Trap> m_result;
+};
+
 class Result {
 public:
     explicit Result(Vector<Value> values)
@@ -183,14 +215,34 @@ public:
     {
     }
 
+    Result(JS::Completion completion)
+        : m_result(move(completion))
+    {
+        VERIFY(m_result.get<JS::Completion>().is_abrupt());
+    }
+
+    Result(PureResult&& result)
+        : m_result(result.m_result.downcast<decltype(m_result)>())
+    {
+    }
+
     auto is_trap() const { return m_result.has<Trap>(); }
+    auto is_completion() const { return m_result.has<JS::Completion>(); }
     auto& values() const { return m_result.get<Vector<Value>>(); }
     auto& values() { return m_result.get<Vector<Value>>(); }
     auto& trap() const { return m_result.get<Trap>(); }
     auto& trap() { return m_result.get<Trap>(); }
+    auto& completion() { return m_result.get<JS::Completion>(); }
+    auto& completion() const { return m_result.get<JS::Completion>(); }
+
+    PureResult assert_wasm_result() &&
+    {
+        VERIFY(!is_completion());
+        return PureResult(move(m_result).downcast<Vector<Value>, Trap>());
+    }
 
 private:
-    Variant<Vector<Value>, Trap> m_result;
+    Variant<Vector<Value>, Trap, JS::Completion> m_result;
 };
 
 using ExternValue = Variant<FunctionAddress, TableAddress, MemoryAddress, GlobalAddress>;

Userland/Libraries/LibWasm/AbstractMachine/BytecodeInterpreter.cpp

@@ -34,7 +34,7 @@ namespace Wasm {
 
 void BytecodeInterpreter::interpret(Configuration& configuration)
 {
-    m_trap.clear();
+    m_trap = Empty {};
     auto& instructions = configuration.frame().expression().instructions();
     auto max_ip_value = InstructionPointer { instructions.size() };
     auto& current_ip_value = configuration.ip();
@@ -51,7 +51,7 @@ void BytecodeInterpreter::interpret(Configuration& configuration)
         auto& instruction = instructions[current_ip_value.value()];
         auto old_ip = current_ip_value;
         interpret(configuration, current_ip_value, instruction);
-        if (m_trap.has_value())
+        if (did_trap())
             return;
         if (current_ip_value == old_ip) // If no jump occurred
             ++current_ip_value;
@@ -140,6 +140,11 @@ void BytecodeInterpreter::call_address(Configuration& configuration, FunctionAdd
         return;
     }
 
+    if (result.is_completion()) {
+        m_trap = move(result.completion());
+        return;
+    }
+
     configuration.stack().entries().ensure_capacity(configuration.stack().size() + result.values().size());
     for (auto& entry : result.values().in_reverse())
         configuration.stack().entries().unchecked_append(move(entry));

Userland/Libraries/LibWasm/AbstractMachine/BytecodeInterpreter.h

@@ -15,9 +15,15 @@ namespace Wasm {
 struct BytecodeInterpreter : public Interpreter {
     virtual void interpret(Configuration&) override;
     virtual ~BytecodeInterpreter() override = default;
-    virtual bool did_trap() const override { return m_trap.has_value(); }
+    virtual bool did_trap() const override { return !m_trap.has<Empty>(); }
-    virtual DeprecatedString trap_reason() const override { return m_trap.value().reason; }
+    virtual DeprecatedString trap_reason() const override
-    virtual void clear_trap() override { m_trap.clear(); }
+    {
+        return m_trap.visit(
+            [](Empty) -> DeprecatedString { VERIFY_NOT_REACHED(); },
+            [](Trap const& trap) { return trap.reason; },
+            [](JS::Completion const& completion) { return completion.value()->to_string_without_side_effects().release_value().to_deprecated_string(); });
+    }
+    virtual void clear_trap() override { m_trap = Empty {}; }
 
     struct CallFrameHandle {
         explicit CallFrameHandle(BytecodeInterpreter& interpreter, Configuration& configuration)
@@ -62,10 +68,10 @@ protected:
     {
         if (!value)
             m_trap = Trap { reason };
-        return m_trap.has_value();
+        return !m_trap.has<Empty>();
     }
 
-    Optional<Trap> m_trap;
+    Variant<Trap, JS::Completion, Empty> m_trap;
     StackInfo m_stack_info;
 };
 

Userland/Libraries/LibWasm/CMakeLists.txt

@@ -8,7 +8,7 @@ set(SOURCES
 )
 
 serenity_lib(LibWasm wasm)
-target_link_libraries(LibWasm PRIVATE LibCore)
+target_link_libraries(LibWasm PRIVATE LibCore LibJS)
 
 # FIXME: Install these into usr/Tests/LibWasm
 include(wasm_spec_tests)

Userland/Libraries/LibWeb/WebAssembly/WebAssemblyObject.cpp

@@ -200,20 +200,12 @@ JS::ThrowCompletionOr<size_t> WebAssemblyObject::instantiate_module(JS::VM& vm,
                             for (auto& entry : arguments)
                                 argument_values.append(to_js_value(vm, entry));
 
-                            auto result_or_error = JS::call(vm, function, JS::js_undefined(), move(argument_values));
+                            auto result = TRY(JS::call(vm, function, JS::js_undefined(), move(argument_values)));
-                            if (result_or_error.is_error()) {
-                                return Wasm::Trap();
-                            }
                             if (type.results().is_empty())
                                 return Wasm::Result { Vector<Wasm::Value> {} };
 
-                            if (type.results().size() == 1) {
+                            if (type.results().size() == 1)
-                                auto value_or_error = to_webassembly_value(vm, result_or_error.release_value(), type.results().first());
+                                return Wasm::Result { Vector<Wasm::Value> { TRY(to_webassembly_value(vm, result, type.results().first())) } };
-                                if (value_or_error.is_error())
-                                    return Wasm::Trap {};
-
-                                return Wasm::Result { Vector<Wasm::Value> { value_or_error.release_value() } };
-                            }
 
                             // FIXME: Multiple returns
                             TODO();

Userland/Utilities/CMakeLists.txt

@@ -133,7 +133,7 @@ target_link_libraries(unzip PRIVATE LibArchive LibCompress LibCrypto)
 target_link_libraries(update-cpp-test-results PRIVATE LibCpp)
 target_link_libraries(useradd PRIVATE LibCrypt)
 target_link_libraries(wallpaper PRIVATE LibGfx LibGUI)
-target_link_libraries(wasm PRIVATE LibWasm LibLine)
+target_link_libraries(wasm PRIVATE LibWasm LibLine LibJS)
 target_link_libraries(wsctl PRIVATE LibGUI LibIPC)
 target_link_libraries(xml PRIVATE LibXML)
 target_link_libraries(zip PRIVATE LibArchive LibCompress LibCrypto)

Userland/Utilities/wasm.cpp

@@ -206,15 +206,17 @@ static bool pre_interpret_hook(Wasm::Configuration& config, Wasm::InstructionPoi
             Wasm::Result result { Wasm::Trap {} };
             {
                 Wasm::BytecodeInterpreter::CallFrameHandle handle { g_interpreter, config };
-                result = config.call(g_interpreter, *address, move(values));
+                result = config.call(g_interpreter, *address, move(values)).assert_wasm_result();
             }
-            if (result.is_trap())
+            if (result.is_trap()) {
                 warnln("Execution trapped: {}", result.trap().reason);
-            if (!result.values().is_empty())
+            } else {
-                warnln("Returned:");
+                if (!result.values().is_empty())
-            for (auto& value : result.values()) {
+                    warnln("Returned:");
-                g_stdout->write("  -> "sv.bytes()).release_value_but_fixme_should_propagate_errors();
+                for (auto& value : result.values()) {
-                g_printer->print(value);
+                    g_stdout->write("  -> "sv.bytes()).release_value_but_fixme_should_propagate_errors();
+                    g_printer->print(value);
+                }
             }
             continue;
         }
@@ -513,7 +515,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
                 outln();
             }
 
-            auto result = machine.invoke(g_interpreter, run_address.value(), move(values));
+            auto result = machine.invoke(g_interpreter, run_address.value(), move(values)).assert_wasm_result();
 
             if (debug)
                 launch_repl();