1 files changed, 198 insertions, 0 deletions
diff --git a/js/src/frontend/AsyncEmitter.cpp b/js/src/frontend/AsyncEmitter.cpp
new file mode 100644
index 0000000000..baa9d87f20
--- /dev/null
+++ b/js/src/frontend/AsyncEmitter.cpp
@@ -0,0 +1,198 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "frontend/AsyncEmitter.h"
+
+#include "mozilla/Assertions.h"  // MOZ_ASSERT
+
+#include "frontend/BytecodeEmitter.h"     // BytecodeEmitter
+#include "frontend/NameOpEmitter.h"       // NameOpEmitter
+#include "vm/AsyncFunctionResolveKind.h"  // AsyncFunctionResolveKind
+#include "vm/Opcodes.h"                   // JSOp
+
+using namespace js;
+using namespace js::frontend;
+
+bool AsyncEmitter::prepareForParamsWithExpression() {
+  MOZ_ASSERT(state_ == State::Start);
+#ifdef DEBUG
+  state_ = State::Parameters;
+#endif
+
+  rejectTryCatch_.emplace(bce_, TryEmitter::Kind::TryCatch,
+                          TryEmitter::ControlKind::NonSyntactic);
+  return rejectTryCatch_->emitTry();
+}
+
+bool AsyncEmitter::prepareForParamsWithoutExpression() {
+  MOZ_ASSERT(state_ == State::Start);
+#ifdef DEBUG
+  state_ = State::Parameters;
+#endif
+  return true;
+}
+
+bool AsyncEmitter::emitParamsEpilogue() {
+  MOZ_ASSERT(state_ == State::Parameters);
+
+  if (rejectTryCatch_) {
+    // If we get here, we need to reset the TryEmitter. Parameters can't reuse
+    // the reject try-catch block from the function body, because the body
+    // may have pushed an additional var-environment. This messes up scope
+    // resolution for the |.generator| variable, because we'd need different
+    // hops to reach |.generator| depending on whether the error was thrown
+    // from the parameters or the function body.
+    if (!emitRejectCatch()) {
+      return false;
+    }
+  }
+
+#ifdef DEBUG
+  state_ = State::PostParams;
+#endif
+  return true;
+}
+
+bool AsyncEmitter::prepareForModule() {
+  // Unlike functions, modules do not have params that we need to worry about.
+  // Instead, this code is for setting up the required generator that will be
+  // used for top level await. Before we can start using top-level await in
+  // modules, we need to emit a
+  // |.generator| which we can use to pause and resume execution.
+  MOZ_ASSERT(state_ == State::Start);
+  MOZ_ASSERT(
+      bce_->lookupName(bce_->cx->parserNames().dotGenerator).hasKnownSlot());
+
+  NameOpEmitter noe(bce_, bce_->cx->parserNames().dotGenerator,
+                    NameOpEmitter::Kind::Initialize);
+  if (!noe.prepareForRhs()) {
+    //        [stack]
+    return false;
+  }
+  if (!bce_->emit1(JSOp::Generator)) {
+    //        [stack] GEN
+    return false;
+  }
+  if (!noe.emitAssignment()) {
+    //        [stack] GEN
+    return false;
+  }
+  if (!bce_->emit1(JSOp::Pop)) {
+    //        [stack]
+    return false;
+  }
+
+#ifdef DEBUG
+  state_ = State::ModulePrologue;
+#endif
+
+  return true;
+}
+
+bool AsyncEmitter::prepareForBody() {
+  MOZ_ASSERT(state_ == State::PostParams || state_ == State::ModulePrologue);
+
+  rejectTryCatch_.emplace(bce_, TryEmitter::Kind::TryCatch,
+                          TryEmitter::ControlKind::NonSyntactic);
+#ifdef DEBUG
+  state_ = State::Body;
+#endif
+  return rejectTryCatch_->emitTry();
+}
+
+bool AsyncEmitter::emitEnd() {
+#ifdef DEBUG
+  MOZ_ASSERT(state_ == State::Body);
+#endif
+
+  if (!emitFinalYield()) {
+    return false;
+  }
+
+  if (!emitRejectCatch()) {
+    return false;
+  }
+
+#ifdef DEBUG
+  state_ = State::End;
+#endif
+  return true;
+}
+
+bool AsyncEmitter::emitFinalYield() {
+  if (!bce_->emit1(JSOp::Undefined)) {
+    //            [stack] UNDEF
+    return false;
+  }
+
+  if (!bce_->emitGetDotGeneratorInInnermostScope()) {
+    //          [stack] UNDEF GEN
+    return false;
+  }
+
+  if (!bce_->emit2(JSOp::AsyncResolve,
+                   uint8_t(AsyncFunctionResolveKind::Fulfill))) {
+    //          [stack] PROMISE
+    return false;
+  }
+
+  if (!bce_->emit1(JSOp::SetRval)) {
+    //            [stack]
+    return false;
+  }
+
+  if (!bce_->emitGetDotGeneratorInInnermostScope()) {
+    //            [stack] GEN
+    return false;
+  }
+
+  if (!bce_->emitYieldOp(JSOp::FinalYieldRval)) {
+    //            [stack]
+    return false;
+  }
+
+  return true;
+}
+
+bool AsyncEmitter::emitRejectCatch() {
+  if (!rejectTryCatch_->emitCatch()) {
+    //              [stack] EXC
+    return false;
+  }
+
+  if (!bce_->emitGetDotGeneratorInInnermostScope()) {
+    //              [stack] EXC GEN
+    return false;
+  }
+
+  if (!bce_->emit2(JSOp::AsyncResolve,
+                   uint8_t(AsyncFunctionResolveKind::Reject))) {
+    //              [stack] PROMISE
+    return false;
+  }
+
+  if (!bce_->emit1(JSOp::SetRval)) {
+    //              [stack]
+    return false;
+  }
+
+  if (!bce_->emitGetDotGeneratorInInnermostScope()) {
+    //              [stack] GEN
+    return false;
+  }
+
+  if (!bce_->emitYieldOp(JSOp::FinalYieldRval)) {
+    //              [stack]
+    return false;
+  }
+
+  if (!rejectTryCatch_->emitEnd()) {
+    return false;
+  }
+
+  rejectTryCatch_.reset();
+  return true;
+}