tools/aidl/generate_rust.cpp

/*
 * Copyright (C) 2020, The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "generate_rust.h"

#include <android-base/stringprintf.h>
#include <android-base/strings.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <map>
#include <memory>
#include <sstream>

#include "aidl_to_common.h"
#include "aidl_to_cpp_common.h"
#include "aidl_to_rust.h"
#include "code_writer.h"
#include "comments.h"
#include "logging.h"

using android::base::Join;
using android::base::Split;
using std::ostringstream;
using std::shared_ptr;
using std::string;
using std::unique_ptr;
using std::vector;

namespace android {
namespace aidl {
namespace rust {

static constexpr const char kArgumentPrefix[] = "_arg_";
static constexpr const char kGetInterfaceVersion[] = "getInterfaceVersion";
static constexpr const char kGetInterfaceHash[] = "getInterfaceHash";

struct MangledAliasVisitor : AidlVisitor {
  CodeWriter& out;
  MangledAliasVisitor(CodeWriter& out) : out(out) {}
  void Visit(const AidlStructuredParcelable& type) override { VisitType(type); }
  void Visit(const AidlInterface& type) override { VisitType(type); }
  void Visit(const AidlEnumDeclaration& type) override { VisitType(type); }
  void Visit(const AidlUnionDecl& type) override { VisitType(type); }
  template <typename T>
  void VisitType(const T& type) {
    out << " pub use " << Qname(type) << " as " << Mangled(type) << ";\n";
  }
  // Return a mangled name for a type (including AIDL package)
  template <typename T>
  string Mangled(const T& type) const {
    ostringstream alias;
    for (const auto& component : Split(type.GetCanonicalName(), ".")) {
      alias << "_" << component.size() << "_" << component;
    }
    return alias.str();
  }
  template <typename T>
  string Typename(const T& type) const {
    if constexpr (std::is_same_v<T, AidlInterface>) {
      return ClassName(type, cpp::ClassNames::INTERFACE);
    } else {
      return type.GetName();
    }
  }
  // Return a fully qualified name for a type in the current file (excluding AIDL package)
  template <typename T>
  string Qname(const T& type) const {
    return Module(type) + "::r#" + Typename(type);
  }
  // Return a module name for a type (relative to the file)
  template <typename T>
  string Module(const T& type) const {
    if (type.GetParentType()) {
      return Module(*type.GetParentType()) + "::r#" + type.GetName();
    } else {
      return "super";
    }
  }
};

void GenerateMangledAliases(CodeWriter& out, const AidlDefinedType& type) {
  MangledAliasVisitor v(out);
  out << "pub(crate) mod mangled {\n";
  VisitTopDown(v, type);
  out << "}\n";
}

string BuildArg(const AidlArgument& arg, const AidlTypenames& typenames, Lifetime lifetime) {
  // We pass in parameters that are not primitives by const reference.
  // Arrays get passed in as slices, which is handled in RustNameOf.
  auto arg_mode = ArgumentStorageMode(arg, typenames);
  auto arg_type = RustNameOf(arg.GetType(), typenames, arg_mode, lifetime);
  return kArgumentPrefix + arg.GetName() + ": " + arg_type;
}

enum class MethodKind {
  // This is a normal non-async method.
  NORMAL,
  // This is an async method. Identical to NORMAL except that async is added
  // in front of `fn`.
  ASYNC,
  // This is an async function, but using a boxed future instead of the async
  // keyword.
  BOXED_FUTURE,
  // This could have been a non-async method, but it returns a Future so that
  // it would not be breaking to make the function do async stuff in the future.
  READY_FUTURE,
};

string BuildMethod(const AidlMethod& method, const AidlTypenames& typenames,
                   const MethodKind kind = MethodKind::NORMAL) {
  // We need to mark the arguments with a lifetime only when returning a future that
  // actually captures the arguments.
  Lifetime lifetime;
  switch (kind) {
    case MethodKind::NORMAL:
    case MethodKind::ASYNC:
    case MethodKind::READY_FUTURE:
      lifetime = Lifetime::NONE;
      break;
    case MethodKind::BOXED_FUTURE:
      lifetime = Lifetime::A;
      break;
  }

  auto method_type = RustNameOf(method.GetType(), typenames, StorageMode::VALUE, lifetime);
  auto return_type = string{"binder::Result<"} + method_type + ">";
  auto fn_prefix = string{""};

  switch (kind) {
    case MethodKind::NORMAL:
      // Don't wrap the return type in anything.
      break;
    case MethodKind::ASYNC:
      fn_prefix = "async ";
      break;
    case MethodKind::BOXED_FUTURE:
      return_type = "binder::BoxFuture<'a, " + return_type + ">";
      break;
    case MethodKind::READY_FUTURE:
      return_type = "std::future::Ready<" + return_type + ">";
      break;
  }

  string parameters = "&" + RustLifetimeName(lifetime) + "self";
  string lifetime_str = RustLifetimeGeneric(lifetime);

  for (const std::unique_ptr<AidlArgument>& arg : method.GetArguments()) {
    parameters += ", ";
    parameters += BuildArg(*arg, typenames, lifetime);
  }

  return fn_prefix + "fn r#" + method.GetName() + lifetime_str + "(" + parameters + ") -> " +
         return_type;
}

void GenerateClientMethodHelpers(CodeWriter& out, const AidlInterface& iface,
                                 const AidlMethod& method, const AidlTypenames& typenames,
                                 const Options& options, const std::string& default_trait_name) {
  string parameters = "&self";
  for (const std::unique_ptr<AidlArgument>& arg : method.GetArguments()) {
    parameters += ", ";
    parameters += BuildArg(*arg, typenames, Lifetime::NONE);
  }

  // Generate build_parcel helper.
  out << "fn build_parcel_" + method.GetName() + "(" + parameters +
             ") -> binder::Result<binder::binder_impl::Parcel> {\n";
  out.Indent();

  out << "let mut aidl_data = self.binder.prepare_transact()?;\n";

  if (iface.IsSensitiveData()) {
    out << "aidl_data.mark_sensitive();\n";
  }

  // Arguments
  for (const std::unique_ptr<AidlArgument>& arg : method.GetArguments()) {
    auto arg_name = kArgumentPrefix + arg->GetName();
    if (arg->IsIn()) {
      // If the argument is already a reference, don't reference it again
      // (unless we turned it into an Option<&T>)
      auto ref_mode = ArgumentReferenceMode(*arg, typenames);
      if (IsReference(ref_mode)) {
        out << "aidl_data.write(" << arg_name << ")?;\n";
      } else {
        out << "aidl_data.write(&" << arg_name << ")?;\n";
      }
    } else if (arg->GetType().IsDynamicArray()) {
      // For out-only arrays, send the array size
      if (arg->GetType().IsNullable()) {
        out << "aidl_data.write_slice_size(" << arg_name << ".as_deref())?;\n";
      } else {
        out << "aidl_data.write_slice_size(Some(" << arg_name << "))?;\n";
      }
    }
  }

  out << "Ok(aidl_data)\n";
  out.Dedent();
  out << "}\n";

  // Generate read_response helper.
  auto return_type = RustNameOf(method.GetType(), typenames, StorageMode::VALUE, Lifetime::NONE);
  out << "fn read_response_" + method.GetName() + "(" + parameters +
             ", _aidl_reply: std::result::Result<binder::binder_impl::Parcel, "
             "binder::StatusCode>) -> binder::Result<" +
             return_type + "> {\n";
  out.Indent();

  // Check for UNKNOWN_TRANSACTION and call the default impl
  if (method.IsUserDefined()) {
    string default_args;
    for (const std::unique_ptr<AidlArgument>& arg : method.GetArguments()) {
      if (!default_args.empty()) {
        default_args += ", ";
      }
      default_args += kArgumentPrefix;
      default_args += arg->GetName();
    }
    out << "if let Err(binder::StatusCode::UNKNOWN_TRANSACTION) = _aidl_reply {\n";
    out << "  if let Some(_aidl_default_impl) = <Self as " << default_trait_name
        << ">::getDefaultImpl() {\n";
    out << "    return _aidl_default_impl.r#" << method.GetName() << "(" << default_args << ");\n";
    out << "  }\n";
    out << "}\n";
  }

  // Return all other errors
  out << "let _aidl_reply = _aidl_reply?;\n";

  string return_val = "()";
  if (!method.IsOneway()) {
    // Check for errors
    out << "let _aidl_status: binder::Status = _aidl_reply.read()?;\n";
    out << "if !_aidl_status.is_ok() { return Err(_aidl_status); }\n";

    // Return reply value
    if (method.GetType().GetName() != "void") {
      auto return_type =
          RustNameOf(method.GetType(), typenames, StorageMode::VALUE, Lifetime::NONE);
      out << "let _aidl_return: " << return_type << " = _aidl_reply.read()?;\n";
      return_val = "_aidl_return";

      if (!method.IsUserDefined()) {
        if (method.GetName() == kGetInterfaceVersion && options.Version() > 0) {
          out << "self.cached_version.store(_aidl_return, std::sync::atomic::Ordering::Relaxed);\n";
        }
        if (method.GetName() == kGetInterfaceHash && !options.Hash().empty()) {
          out << "*self.cached_hash.lock().unwrap() = Some(_aidl_return.clone());\n";
        }
      }
    }

    for (const AidlArgument* arg : method.GetOutArguments()) {
      out << "_aidl_reply.read_onto(" << kArgumentPrefix << arg->GetName() << ")?;\n";
    }
  }

  // Return the result
  out << "Ok(" << return_val << ")\n";

  out.Dedent();
  out << "}\n";
}

void GenerateClientMethod(CodeWriter& out, const AidlInterface& iface, const AidlMethod& method,
                          const AidlTypenames& typenames, const Options& options,
                          const MethodKind kind) {
  // Generate the method
  out << BuildMethod(method, typenames, kind) << " {\n";
  out.Indent();

  if (!method.IsUserDefined()) {
    if (method.GetName() == kGetInterfaceVersion && options.Version() > 0) {
      // Check if the version is in the cache
      out << "let _aidl_version = "
             "self.cached_version.load(std::sync::atomic::Ordering::Relaxed);\n";
      switch (kind) {
        case MethodKind::NORMAL:
        case MethodKind::ASYNC:
          out << "if _aidl_version != -1 { return Ok(_aidl_version); }\n";
          break;
        case MethodKind::BOXED_FUTURE:
          out << "if _aidl_version != -1 { return Box::pin(std::future::ready(Ok(_aidl_version))); "
                 "}\n";
          break;
        case MethodKind::READY_FUTURE:
          out << "if _aidl_version != -1 { return std::future::ready(Ok(_aidl_version)); }\n";
          break;
      }
    }

    if (method.GetName() == kGetInterfaceHash && !options.Hash().empty()) {
      out << "{\n";
      out << "  let _aidl_hash_lock = self.cached_hash.lock().unwrap();\n";
      out << "  if let Some(ref _aidl_hash) = *_aidl_hash_lock {\n";
      switch (kind) {
        case MethodKind::NORMAL:
        case MethodKind::ASYNC:
          out << "    return Ok(_aidl_hash.clone());\n";
          break;
        case MethodKind::BOXED_FUTURE:
          out << "    return Box::pin(std::future::ready(Ok(_aidl_hash.clone())));\n";
          break;
        case MethodKind::READY_FUTURE:
          out << "    return std::future::ready(Ok(_aidl_hash.clone()));\n";
          break;
      }
      out << "  }\n";
      out << "}\n";
    }
  }

  string build_parcel_args;
  for (const std::unique_ptr<AidlArgument>& arg : method.GetArguments()) {
    if (!build_parcel_args.empty()) {
      build_parcel_args += ", ";
    }
    build_parcel_args += kArgumentPrefix;
    build_parcel_args += arg->GetName();
  }

  string read_response_args =
      build_parcel_args.empty() ? "_aidl_reply" : build_parcel_args + ", _aidl_reply";

  vector<string> flags;
  if (method.IsOneway()) flags.push_back("binder::binder_impl::FLAG_ONEWAY");
  if (iface.IsSensitiveData()) flags.push_back("binder::binder_impl::FLAG_CLEAR_BUF");
  flags.push_back("binder::binder_impl::FLAG_PRIVATE_LOCAL");

  string transact_flags = flags.empty() ? "0" : Join(flags, " | ");

  switch (kind) {
    case MethodKind::NORMAL:
    case MethodKind::ASYNC:
      if (method.IsNew() && ShouldForceDowngradeFor(CommunicationSide::WRITE) &&
          method.IsUserDefined()) {
        out << "if (true) {\n";
        out << " return Err(binder::Status::from(binder::StatusCode::UNKNOWN_TRANSACTION));\n";
        out << "} else {\n";
        out.Indent();
      }
      // Prepare transaction.
      out << "let _aidl_data = self.build_parcel_" + method.GetName() + "(" + build_parcel_args +
                 ")?;\n";
      // Submit transaction.
      out << "let _aidl_reply = self.binder.submit_transact(transactions::r#" << method.GetName()
          << ", _aidl_data, " << transact_flags << ");\n";
      // Deserialize response.
      out << "self.read_response_" + method.GetName() + "(" + read_response_args + ")\n";
      break;
    case MethodKind::READY_FUTURE:
      if (method.IsNew() && ShouldForceDowngradeFor(CommunicationSide::WRITE) &&
          method.IsUserDefined()) {
        out << "if (true) {\n";
        out << " return "
               "std::future::ready(Err(binder::Status::from(binder::StatusCode::UNKNOWN_"
               "TRANSACTION)));\n";
        out << "} else {\n";
        out.Indent();
      }
      // Prepare transaction.
      out << "let _aidl_data = match self.build_parcel_" + method.GetName() + "(" +
                 build_parcel_args + ") {\n";
      out.Indent();
      out << "Ok(_aidl_data) => _aidl_data,\n";
      out << "Err(err) => return std::future::ready(Err(err)),\n";
      out.Dedent();
      out << "};\n";
      // Submit transaction.
      out << "let _aidl_reply = self.binder.submit_transact(transactions::r#" << method.GetName()
          << ", _aidl_data, " << transact_flags << ");\n";
      // Deserialize response.
      out << "std::future::ready(self.read_response_" + method.GetName() + "(" +
                 read_response_args + "))\n";
      break;
    case MethodKind::BOXED_FUTURE:
      if (method.IsNew() && ShouldForceDowngradeFor(CommunicationSide::WRITE) &&
          method.IsUserDefined()) {
        out << "if (true) {\n";
        out << " return "
               "Box::pin(std::future::ready(Err(binder::Status::from(binder::StatusCode::UNKNOWN_"
               "TRANSACTION))));\n";
        out << "} else {\n";
        out.Indent();
      }
      // Prepare transaction.
      out << "let _aidl_data = match self.build_parcel_" + method.GetName() + "(" +
                 build_parcel_args + ") {\n";
      out.Indent();
      out << "Ok(_aidl_data) => _aidl_data,\n";
      out << "Err(err) => return Box::pin(std::future::ready(Err(err))),\n";
      out.Dedent();
      out << "};\n";
      // Submit transaction.
      out << "let binder = self.binder.clone();\n";
      out << "P::spawn(\n";
      out.Indent();
      out << "move || binder.submit_transact(transactions::r#" << method.GetName()
          << ", _aidl_data, " << transact_flags << "),\n";
      out << "move |_aidl_reply| async move {\n";
      out.Indent();
      // Deserialize response.
      out << "self.read_response_" + method.GetName() + "(" + read_response_args + ")\n";
      out.Dedent();
      out << "}\n";
      out.Dedent();
      out << ")\n";
      break;
  }

  if (method.IsNew() && ShouldForceDowngradeFor(CommunicationSide::WRITE) &&
      method.IsUserDefined()) {
    out.Dedent();
    out << "}\n";
  }
  out.Dedent();
  out << "}\n";
}

void GenerateServerTransaction(CodeWriter& out, const AidlInterface& interface,
                               const AidlMethod& method, const AidlTypenames& typenames) {
  out << "transactions::r#" << method.GetName() << " => {\n";
  out.Indent();
  if (method.IsUserDefined() && method.IsNew() &&
      ShouldForceDowngradeFor(CommunicationSide::READ)) {
    out << "if (true) {\n";
    out << "  Err(binder::StatusCode::UNKNOWN_TRANSACTION)\n";
    out << "} else {\n";
    out.Indent();
  }

  if (interface.EnforceExpression() || method.GetType().EnforceExpression()) {
    out << "compile_error!(\"Permission checks not support for the Rust backend\");\n";
  }

  string args;
  for (const auto& arg : method.GetArguments()) {
    string arg_name = kArgumentPrefix + arg->GetName();
    StorageMode arg_mode;
    if (arg->IsIn()) {
      arg_mode = StorageMode::VALUE;
    } else {
      // We need a value we can call Default::default() on
      arg_mode = StorageMode::DEFAULT_VALUE;
    }
    auto arg_type = RustNameOf(arg->GetType(), typenames, arg_mode, Lifetime::NONE);

    string arg_mut = arg->IsOut() ? "mut " : "";
    string arg_init = arg->IsIn() ? "_aidl_data.read()?" : "Default::default()";
    out << "let " << arg_mut << arg_name << ": " << arg_type << " = " << arg_init << ";\n";
    if (!arg->IsIn() && arg->GetType().IsDynamicArray()) {
      // _aidl_data.resize_[nullable_]out_vec(&mut _arg_foo)?;
      auto resize_name = arg->GetType().IsNullable() ? "resize_nullable_out_vec" : "resize_out_vec";
      out << "_aidl_data." << resize_name << "(&mut " << arg_name << ")?;\n";
    }

    auto ref_mode = ArgumentReferenceMode(*arg, typenames);
    if (!args.empty()) {
      args += ", ";
    }
    args += TakeReference(ref_mode, arg_name);
  }
  out << "let _aidl_return = _aidl_service.r#" << method.GetName() << "(" << args << ");\n";

  if (!method.IsOneway()) {
    out << "match &_aidl_return {\n";
    out.Indent();
    out << "Ok(_aidl_return) => {\n";
    out.Indent();
    out << "_aidl_reply.write(&binder::Status::from(binder::StatusCode::OK))?;\n";
    if (method.GetType().GetName() != "void") {
      out << "_aidl_reply.write(_aidl_return)?;\n";
    }

    // Serialize out arguments
    for (const AidlArgument* arg : method.GetOutArguments()) {
      string arg_name = kArgumentPrefix + arg->GetName();

      auto& arg_type = arg->GetType();
      if (!arg->IsIn() && arg_type.IsArray() && arg_type.GetName() == "ParcelFileDescriptor") {
        // We represent arrays of ParcelFileDescriptor as
        // Vec<Option<ParcelFileDescriptor>> when they're out-arguments,
        // but we need all of them to be initialized to Some; if there's
        // any None, return UNEXPECTED_NULL (this is what libbinder_ndk does)
        out << "if " << arg_name << ".iter().any(Option::is_none) { "
            << "return Err(binder::StatusCode::UNEXPECTED_NULL); }\n";
      } else if (!arg->IsIn() && TypeNeedsOption(arg_type, typenames)) {
        // Unwrap out-only arguments that we wrapped in Option<T>
        out << "let " << arg_name << " = " << arg_name
            << ".ok_or(binder::StatusCode::UNEXPECTED_NULL)?;\n";
      }

      out << "_aidl_reply.write(&" << arg_name << ")?;\n";
    }
    out.Dedent();
    out << "}\n";
    out << "Err(_aidl_status) => _aidl_reply.write(_aidl_status)?\n";
    out.Dedent();
    out << "}\n";
  }
  out << "Ok(())\n";
  if (method.IsUserDefined() && method.IsNew() &&
      ShouldForceDowngradeFor(CommunicationSide::READ)) {
    out.Dedent();
    out << "}\n";
  }
  out.Dedent();
  out << "}\n";
}

void GenerateServerItems(CodeWriter& out, const AidlInterface* iface,
                         const AidlTypenames& typenames) {
  auto trait_name = ClassName(*iface, cpp::ClassNames::INTERFACE);
  auto server_name = ClassName(*iface, cpp::ClassNames::SERVER);

  // Forward all IFoo functions from Binder to the inner object
  out << "impl " << trait_name << " for binder::binder_impl::Binder<" << server_name << "> {\n";
  out.Indent();
  for (const auto& method : iface->GetMethods()) {
    string args;
    for (const std::unique_ptr<AidlArgument>& arg : method->GetArguments()) {
      if (!args.empty()) {
        args += ", ";
      }
      args += kArgumentPrefix;
      args += arg->GetName();
    }
    out << BuildMethod(*method, typenames) << " { "
        << "self.0.r#" << method->GetName() << "(" << args << ") }\n";
  }
  out.Dedent();
  out << "}\n";

  out << "fn on_transact("
         "_aidl_service: &dyn "
      << trait_name
      << ", "
         "_aidl_code: binder::binder_impl::TransactionCode, "
         "_aidl_data: &binder::binder_impl::BorrowedParcel<'_>, "
         "_aidl_reply: &mut binder::binder_impl::BorrowedParcel<'_>) -> std::result::Result<(), "
         "binder::StatusCode> "
         "{\n";
  out.Indent();
  out << "match _aidl_code {\n";
  out.Indent();
  for (const auto& method : iface->GetMethods()) {
    GenerateServerTransaction(out, *iface, *method, typenames);
  }
  out << "_ => Err(binder::StatusCode::UNKNOWN_TRANSACTION)\n";
  out.Dedent();
  out << "}\n";
  out.Dedent();
  out << "}\n";
}

void GenerateDeprecated(CodeWriter& out, const AidlCommentable& type) {
  if (auto deprecated = FindDeprecated(type.GetComments()); deprecated.has_value()) {
    if (deprecated->note.empty()) {
      out << "#[deprecated]\n";
    } else {
      out << "#[deprecated = " << QuotedEscape(deprecated->note) << "]\n";
    }
  }
}

template <typename TypeWithConstants>
void GenerateConstantDeclarations(CodeWriter& out, const TypeWithConstants& type,
                                  const AidlTypenames& typenames) {
  for (const auto& constant : type.GetConstantDeclarations()) {
    const AidlTypeSpecifier& type = constant->GetType();
    const AidlConstantValue& value = constant->GetValue();

    string const_type;
    if (type.Signature() == "String") {
      const_type = "&str";
    } else if (type.Signature() == "byte" || type.Signature() == "int" ||
               type.Signature() == "long" || type.Signature() == "float" ||
               type.Signature() == "double") {
      const_type = RustNameOf(type, typenames, StorageMode::VALUE, Lifetime::NONE);
    } else {
      AIDL_FATAL(value) << "Unrecognized constant type: " << type.Signature();
    }

    GenerateDeprecated(out, *constant);
    out << "pub const r#" << constant->GetName() << ": " << const_type << " = "
        << constant->ValueString(ConstantValueDecoratorRef) << ";\n";
  }
}

void GenerateRustInterface(CodeWriter* code_writer, const AidlInterface* iface,
                           const AidlTypenames& typenames, const Options& options) {
  *code_writer << "#![allow(non_upper_case_globals)]\n";
  *code_writer << "#![allow(non_snake_case)]\n";
  // Import IBinderInternal for transact()
  *code_writer << "#[allow(unused_imports)] use binder::binder_impl::IBinderInternal;\n";

  auto trait_name = ClassName(*iface, cpp::ClassNames::INTERFACE);
  auto trait_name_async = trait_name + "Async";
  auto trait_name_async_server = trait_name + "AsyncServer";
  auto client_name = ClassName(*iface, cpp::ClassNames::CLIENT);
  auto server_name = ClassName(*iface, cpp::ClassNames::SERVER);
  *code_writer << "use binder::declare_binder_interface;\n";
  *code_writer << "declare_binder_interface! {\n";
  code_writer->Indent();
  *code_writer << trait_name << "[\"" << iface->GetDescriptor() << "\"] {\n";
  code_writer->Indent();
  *code_writer << "native: " << server_name << "(on_transact),\n";
  *code_writer << "proxy: " << client_name << " {\n";
  code_writer->Indent();
  if (options.Version() > 0) {
    string comma = options.Hash().empty() ? "" : ",";
    *code_writer << "cached_version: "
                    "std::sync::atomic::AtomicI32 = "
                    "std::sync::atomic::AtomicI32::new(-1)"
                 << comma << "\n";
  }
  if (!options.Hash().empty()) {
    *code_writer << "cached_hash: "
                    "std::sync::Mutex<Option<String>> = "
                    "std::sync::Mutex::new(None)\n";
  }
  code_writer->Dedent();
  *code_writer << "},\n";
  *code_writer << "async: " << trait_name_async << ",\n";
  if (iface->IsVintfStability()) {
    *code_writer << "stability: binder::binder_impl::Stability::Vintf,\n";
  }
  code_writer->Dedent();
  *code_writer << "}\n";
  code_writer->Dedent();
  *code_writer << "}\n";

  // Emit the trait.
  GenerateDeprecated(*code_writer, *iface);
  *code_writer << "pub trait " << trait_name << ": binder::Interface + Send {\n";
  code_writer->Indent();
  *code_writer << "fn get_descriptor() -> &'static str where Self: Sized { \""
               << iface->GetDescriptor() << "\" }\n";

  for (const auto& method : iface->GetMethods()) {
    // Generate the method
    GenerateDeprecated(*code_writer, *method);
    if (method->IsUserDefined()) {
      *code_writer << BuildMethod(*method, typenames) << ";\n";
    } else {
      // Generate default implementations for meta methods
      *code_writer << BuildMethod(*method, typenames) << " {\n";
      code_writer->Indent();
      if (method->GetName() == kGetInterfaceVersion && options.Version() > 0) {
        *code_writer << "Ok(VERSION)\n";
      } else if (method->GetName() == kGetInterfaceHash && !options.Hash().empty()) {
        *code_writer << "Ok(HASH.into())\n";
      }
      code_writer->Dedent();
      *code_writer << "}\n";
    }
  }

  // Emit the default implementation code inside the trait
  auto default_trait_name = ClassName(*iface, cpp::ClassNames::DEFAULT_IMPL);
  auto default_ref_name = default_trait_name + "Ref";
  *code_writer << "fn getDefaultImpl()"
               << " -> " << default_ref_name << " where Self: Sized {\n";
  *code_writer << "  DEFAULT_IMPL.lock().unwrap().clone()\n";
  *code_writer << "}\n";
  *code_writer << "fn setDefaultImpl(d: " << default_ref_name << ")"
               << " -> " << default_ref_name << " where Self: Sized {\n";
  *code_writer << "  std::mem::replace(&mut *DEFAULT_IMPL.lock().unwrap(), d)\n";
  *code_writer << "}\n";
  code_writer->Dedent();
  *code_writer << "}\n";

  // Emit the async trait.
  GenerateDeprecated(*code_writer, *iface);
  *code_writer << "pub trait " << trait_name_async << "<P>: binder::Interface + Send {\n";
  code_writer->Indent();
  *code_writer << "fn get_descriptor() -> &'static str where Self: Sized { \""
               << iface->GetDescriptor() << "\" }\n";

  for (const auto& method : iface->GetMethods()) {
    // Generate the method
    GenerateDeprecated(*code_writer, *method);

    MethodKind kind = method->IsOneway() ? MethodKind::READY_FUTURE : MethodKind::BOXED_FUTURE;

    if (method->IsUserDefined()) {
      *code_writer << BuildMethod(*method, typenames, kind) << ";\n";
    } else {
      // Generate default implementations for meta methods
      *code_writer << BuildMethod(*method, typenames, kind) << " {\n";
      code_writer->Indent();
      if (method->GetName() == kGetInterfaceVersion && options.Version() > 0) {
        *code_writer << "Box::pin(async move { Ok(VERSION) })\n";
      } else if (method->GetName() == kGetInterfaceHash && !options.Hash().empty()) {
        *code_writer << "Box::pin(async move { Ok(HASH.into()) })\n";
      }
      code_writer->Dedent();
      *code_writer << "}\n";
    }
  }
  code_writer->Dedent();
  *code_writer << "}\n";

  // Emit the async server trait.
  GenerateDeprecated(*code_writer, *iface);
  *code_writer << "#[::async_trait::async_trait]\n";
  *code_writer << "pub trait " << trait_name_async_server << ": binder::Interface + Send {\n";
  code_writer->Indent();
  *code_writer << "fn get_descriptor() -> &'static str where Self: Sized { \""
               << iface->GetDescriptor() << "\" }\n";

  for (const auto& method : iface->GetMethods()) {
    // Generate the method
    if (method->IsUserDefined()) {
      GenerateDeprecated(*code_writer, *method);
      *code_writer << BuildMethod(*method, typenames, MethodKind::ASYNC) << ";\n";
    }
  }
  code_writer->Dedent();
  *code_writer << "}\n";

  // Emit a new_async_binder method for binding an async server.
  *code_writer << "impl " << server_name << " {\n";
  code_writer->Indent();
  *code_writer << "/// Create a new async binder service.\n";
  *code_writer << "pub fn new_async_binder<T, R>(inner: T, rt: R, features: "
                  "binder::BinderFeatures) -> binder::Strong<dyn "
               << trait_name << ">\n";
  *code_writer << "where\n";
  code_writer->Indent();
  *code_writer << "T: " << trait_name_async_server
               << " + binder::Interface + Send + Sync + 'static,\n";
  *code_writer << "R: binder::binder_impl::BinderAsyncRuntime + Send + Sync + 'static,\n";
  code_writer->Dedent();
  *code_writer << "{\n";
  code_writer->Indent();
  // Define a wrapper struct that implements the non-async trait by calling block_on.
  *code_writer << "struct Wrapper<T, R> {\n";
  code_writer->Indent();
  *code_writer << "_inner: T,\n";
  *code_writer << "_rt: R,\n";
  code_writer->Dedent();
  *code_writer << "}\n";
  *code_writer << "impl<T, R> binder::Interface for Wrapper<T, R> where T: binder::Interface, R: "
                  "Send + Sync + 'static {\n";
  code_writer->Indent();
  *code_writer << "fn as_binder(&self) -> binder::SpIBinder { self._inner.as_binder() }\n";
  *code_writer
      << "fn dump(&self, _writer: &mut dyn std::io::Write, _args: "
         "&[&std::ffi::CStr]) -> "
         "std::result::Result<(), binder::StatusCode> { self._inner.dump(_writer, _args) }\n";
  code_writer->Dedent();
  *code_writer << "}\n";
  *code_writer << "impl<T, R> " << trait_name << " for Wrapper<T, R>\n";
  *code_writer << "where\n";
  code_writer->Indent();
  *code_writer << "T: " << trait_name_async_server << " + Send + Sync + 'static,\n";
  *code_writer << "R: binder::binder_impl::BinderAsyncRuntime + Send + Sync + 'static,\n";
  code_writer->Dedent();
  *code_writer << "{\n";
  code_writer->Indent();
  for (const auto& method : iface->GetMethods()) {
    // Generate the method
    if (method->IsUserDefined()) {
      string args = "";
      for (const std::unique_ptr<AidlArgument>& arg : method->GetArguments()) {
        if (!args.empty()) {
          args += ", ";
        }
        args += kArgumentPrefix;
        args += arg->GetName();
      }

      *code_writer << BuildMethod(*method, typenames) << " {\n";
      code_writer->Indent();
      *code_writer << "self._rt.block_on(self._inner.r#" << method->GetName() << "(" << args
                   << "))\n";
      code_writer->Dedent();
      *code_writer << "}\n";
    }
  }
  code_writer->Dedent();
  *code_writer << "}\n";

  *code_writer << "let wrapped = Wrapper { _inner: inner, _rt: rt };\n";
  *code_writer << "Self::new_binder(wrapped, features)\n";

  code_writer->Dedent();
  *code_writer << "}\n";
  code_writer->Dedent();
  *code_writer << "}\n";

  // Emit the default trait
  *code_writer << "pub trait " << default_trait_name << ": Send + Sync {\n";
  code_writer->Indent();
  for (const auto& method : iface->GetMethods()) {
    if (!method->IsUserDefined()) {
      continue;
    }

    // Generate the default method
    *code_writer << BuildMethod(*method, typenames) << " {\n";
    code_writer->Indent();
    *code_writer << "Err(binder::StatusCode::UNKNOWN_TRANSACTION.into())\n";
    code_writer->Dedent();
    *code_writer << "}\n";
  }
  code_writer->Dedent();
  *code_writer << "}\n";

  // Generate the transaction code constants
  // The constants get their own sub-module to avoid conflicts
  *code_writer << "pub mod transactions {\n";
  code_writer->Indent();
  for (const auto& method : iface->GetMethods()) {
    // Generate the transaction code constant
    *code_writer << "pub const r#" << method->GetName()
                 << ": binder::binder_impl::TransactionCode = "
                    "binder::binder_impl::FIRST_CALL_TRANSACTION + " +
                        std::to_string(method->GetId()) + ";\n";
  }
  code_writer->Dedent();
  *code_writer << "}\n";

  // Emit the default implementation code outside the trait
  *code_writer << "pub type " << default_ref_name << " = Option<std::sync::Arc<dyn "
               << default_trait_name << ">>;\n";
  *code_writer << "static DEFAULT_IMPL: std::sync::Mutex<" << default_ref_name
               << "> = std::sync::Mutex::new(None);\n";

  // Emit the interface constants
  GenerateConstantDeclarations(*code_writer, *iface, typenames);

  // Emit VERSION and HASH
  // These need to be top-level item constants instead of associated consts
  // because the latter are incompatible with trait objects, see
  // https://doc.rust-lang.org/reference/items/traits.html#object-safety
  if (options.Version() > 0) {
    if (options.IsLatestUnfrozenVersion()) {
      *code_writer << "pub const VERSION: i32 = if true {"
                   << std::to_string(options.PreviousVersion()) << "} else {"
                   << std::to_string(options.Version()) << "};\n";
    } else {
      *code_writer << "pub const VERSION: i32 = " << std::to_string(options.Version()) << ";\n";
    }
  }
  if (!options.Hash().empty() || options.IsLatestUnfrozenVersion()) {
    if (options.IsLatestUnfrozenVersion()) {
      *code_writer << "pub const HASH: &str = if true {\"" << options.PreviousHash()
                   << "\"} else {\"" << options.Hash() << "\"};\n";
    } else {
      *code_writer << "pub const HASH: &str = \"" << options.Hash() << "\";\n";
    }
  }

  // Generate the client-side method helpers
  //
  // The methods in this block are not marked pub, so they are not accessible from outside the
  // AIDL generated code.
  *code_writer << "impl " << client_name << " {\n";
  code_writer->Indent();
  for (const auto& method : iface->GetMethods()) {
    GenerateClientMethodHelpers(*code_writer, *iface, *method, typenames, options, trait_name);
  }
  code_writer->Dedent();
  *code_writer << "}\n";

  // Generate the client-side methods
  *code_writer << "impl " << trait_name << " for " << client_name << " {\n";
  code_writer->Indent();
  for (const auto& method : iface->GetMethods()) {
    GenerateClientMethod(*code_writer, *iface, *method, typenames, options, MethodKind::NORMAL);
  }
  code_writer->Dedent();
  *code_writer << "}\n";

  // Generate the async client-side methods
  *code_writer << "impl<P: binder::BinderAsyncPool> " << trait_name_async << "<P> for "
               << client_name << " {\n";
  code_writer->Indent();
  for (const auto& method : iface->GetMethods()) {
    MethodKind kind = method->IsOneway() ? MethodKind::READY_FUTURE : MethodKind::BOXED_FUTURE;
    GenerateClientMethod(*code_writer, *iface, *method, typenames, options, kind);
  }
  code_writer->Dedent();
  *code_writer << "}\n";

  // Generate the server-side methods
  GenerateServerItems(*code_writer, iface, typenames);
}

void RemoveUsed(std::set<std::string>* params, const AidlTypeSpecifier& type) {
  if (!type.IsResolved()) {
    params->erase(type.GetName());
  }
  if (type.IsGeneric()) {
    for (const auto& param : type.GetTypeParameters()) {
      RemoveUsed(params, *param);
    }
  }
}

std::set<std::string> FreeParams(const AidlStructuredParcelable* parcel) {
  if (!parcel->IsGeneric()) {
    return std::set<std::string>();
  }
  auto typeParams = parcel->GetTypeParameters();
  std::set<std::string> unusedParams(typeParams.begin(), typeParams.end());
  for (const auto& variable : parcel->GetFields()) {
    RemoveUsed(&unusedParams, variable->GetType());
  }
  return unusedParams;
}

void WriteParams(CodeWriter& out, const AidlParameterizable<std::string>* parcel,
                 std::string extra) {
  if (parcel->IsGeneric()) {
    out << "<";
    for (const auto& param : parcel->GetTypeParameters()) {
      out << param << extra << ",";
    }
    out << ">";
  }
}

void WriteParams(CodeWriter& out, const AidlParameterizable<std::string>* parcel) {
  WriteParams(out, parcel, "");
}

static void GeneratePaddingField(CodeWriter& out, const std::string& field_type, size_t struct_size,
                                 size_t& padding_index, const std::string& padding_element) {
  // If current field is i64 or f64, generate padding for previous field. AIDL enums
  // backed by these types have structs with alignment attributes generated so we only need to
  // take primitive types that have variable alignment across archs into account here.
  if (field_type == "i64" || field_type == "f64") {
    // Align total struct size to 8 bytes since current field should have 8 byte alignment
    auto padding_size = cpp::AlignTo(struct_size, 8) - struct_size;
    if (padding_size != 0) {
      out << "_pad_" << std::to_string(padding_index) << ": [" << padding_element << "; "
          << std::to_string(padding_size) << "],\n";
      padding_index += 1;
    }
  }
}

void GenerateParcelBody(CodeWriter& out, const AidlStructuredParcelable* parcel,
                        const AidlTypenames& typenames) {
  GenerateDeprecated(out, *parcel);
  auto parcelable_alignment = cpp::AlignmentOfDefinedType(*parcel, typenames);
  if (parcelable_alignment || parcel->IsFixedSize()) {
    AIDL_FATAL_IF(!parcel->IsFixedSize(), parcel);
    AIDL_FATAL_IF(parcelable_alignment == std::nullopt, parcel);
    // i64/f64 are aligned to 4 bytes on x86 which may underalign the whole struct if it's the
    // largest field so we need to set the alignment manually as if these types were aligned to 8
    // bytes.
    out << "#[repr(C, align(" << std::to_string(*parcelable_alignment) << "))]\n";
  }
  out << "pub struct r#" << parcel->GetName();
  WriteParams(out, parcel);
  out << " {\n";
  out.Indent();
  const auto& fields = parcel->GetFields();
  // empty structs in C++ are 1 byte so generate an unused field in this case to make the layouts
  // match
  if (fields.size() == 0 && parcel->IsFixedSize()) {
    out << "_unused: u8,\n";
  } else {
    size_t padding_index = 0;
    size_t struct_size = 0;
    for (const auto& variable : fields) {
      GenerateDeprecated(out, *variable);
      const auto& var_type = variable->GetType();
      auto field_type =
          RustNameOf(var_type, typenames, StorageMode::PARCELABLE_FIELD, Lifetime::NONE);
      if (parcel->IsFixedSize()) {
        GeneratePaddingField(out, field_type, struct_size, padding_index, "u8");

        auto alignment = cpp::AlignmentOf(var_type, typenames);
        AIDL_FATAL_IF(alignment == std::nullopt, var_type);
        struct_size = cpp::AlignTo(struct_size, *alignment);
        auto var_size = cpp::SizeOf(var_type, typenames);
        AIDL_FATAL_IF(var_size == std::nullopt, var_type);
        struct_size += *var_size;
      }
      out << "pub r#" << variable->GetName() << ": " << field_type << ",\n";
    }
    for (const auto& unused_param : FreeParams(parcel)) {
      out << "_phantom_" << unused_param << ": std::marker::PhantomData<" << unused_param << ">,\n";
    }
  }
  out.Dedent();
  out << "}\n";
  if (parcel->IsFixedSize()) {
    size_t variable_offset = 0;
    for (const auto& variable : fields) {
      const auto& var_type = variable->GetType();
      // Assert the offset of each field within the struct
      auto alignment = cpp::AlignmentOf(var_type, typenames);
      AIDL_FATAL_IF(alignment == std::nullopt, var_type);
      variable_offset = cpp::AlignTo(variable_offset, *alignment);
      out << "static_assertions::const_assert_eq!(std::mem::offset_of!(" << parcel->GetName()
          << ", r#" << variable->GetName() << "), " << std::to_string(variable_offset) << ");\n";

      // Assert the size of each field
      auto variable_size = cpp::SizeOf(var_type, typenames);
      AIDL_FATAL_IF(variable_size == std::nullopt, var_type);
      std::string rust_type =
          RustNameOf(var_type, typenames, StorageMode::PARCELABLE_FIELD, Lifetime::NONE);
      out << "static_assertions::const_assert_eq!(std::mem::size_of::<" << rust_type << ">(), "
          << std::to_string(*variable_size) << ");\n";

      variable_offset += *variable_size;
    }
    // Assert the alignment of the struct
    auto parcelable_alignment = cpp::AlignmentOfDefinedType(*parcel, typenames);
    AIDL_FATAL_IF(parcelable_alignment == std::nullopt, *parcel);
    out << "static_assertions::const_assert_eq!(std::mem::align_of::<" << parcel->GetName()
        << ">(), " << std::to_string(*parcelable_alignment) << ");\n";

    // Assert the size of the struct
    auto parcelable_size = cpp::SizeOfDefinedType(*parcel, typenames);
    AIDL_FATAL_IF(parcelable_size == std::nullopt, *parcel);
    out << "static_assertions::const_assert_eq!(std::mem::size_of::<" << parcel->GetName()
        << ">(), " << std::to_string(*parcelable_size) << ");\n";
  }
}

void GenerateParcelDefault(CodeWriter& out, const AidlStructuredParcelable* parcel,
                           const AidlTypenames& typenames) {
  out << "impl";
  WriteParams(out, parcel, ": Default");
  out << " Default for r#" << parcel->GetName();
  WriteParams(out, parcel);
  out << " {\n";
  out.Indent();
  out << "fn default() -> Self {\n";
  out.Indent();
  out << "Self {\n";
  out.Indent();
  size_t padding_index = 0;
  size_t struct_size = 0;
  const auto& fields = parcel->GetFields();
  if (fields.size() == 0 && parcel->IsFixedSize()) {
    out << "_unused: 0,\n";
  } else {
    for (const auto& variable : fields) {
      const auto& var_type = variable->GetType();
      // Generate initializer for padding for previous field if current field is i64 or f64
      if (parcel->IsFixedSize()) {
        auto field_type =
            RustNameOf(var_type, typenames, StorageMode::PARCELABLE_FIELD, Lifetime::NONE);
        GeneratePaddingField(out, field_type, struct_size, padding_index, "0");

        auto alignment = cpp::AlignmentOf(var_type, typenames);
        AIDL_FATAL_IF(alignment == std::nullopt, var_type);
        struct_size = cpp::AlignTo(struct_size, *alignment);

        auto var_size = cpp::SizeOf(var_type, typenames);
        AIDL_FATAL_IF(var_size == std::nullopt, var_type);
        struct_size += *var_size;
      }

      out << "r#" << variable->GetName() << ": ";
      if (variable->GetDefaultValue()) {
        out << variable->ValueString(ConstantValueDecorator);
      } else {
        // Some types don't implement "Default".
        // - ParcelableHolder
        // - Arrays
        if (variable->GetType().GetName() == "ParcelableHolder") {
          out << "binder::ParcelableHolder::new(";
          if (parcel->IsVintfStability()) {
            out << "binder::binder_impl::Stability::Vintf";
          } else {
            out << "binder::binder_impl::Stability::Local";
          }
          out << ")";
        } else if (variable->GetType().IsFixedSizeArray() && !variable->GetType().IsNullable()) {
          out << ArrayDefaultValue(variable->GetType());
        } else {
          out << "Default::default()";
        }
      }
      out << ",\n";
    }
    for (const auto& unused_param : FreeParams(parcel)) {
      out << "r#_phantom_" << unused_param << ": Default::default(),\n";
    }
  }
  out.Dedent();
  out << "}\n";
  out.Dedent();
  out << "}\n";
  out.Dedent();
  out << "}\n";
}

void GenerateParcelSerializeBody(CodeWriter& out, const AidlStructuredParcelable* parcel,
                                 const AidlTypenames& typenames) {
  out << "parcel.sized_write(|subparcel| {\n";
  out.Indent();
  for (const auto& variable : parcel->GetFields()) {
    if (variable->IsNew() && ShouldForceDowngradeFor(CommunicationSide::WRITE)) {
      out << "if (false) {\n";
      out.Indent();
    }
    if (TypeNeedsOption(variable->GetType(), typenames)) {
      out << "let __field_ref = self.r#" << variable->GetName()
          << ".as_ref().ok_or(binder::StatusCode::UNEXPECTED_NULL)?;\n";
      out << "subparcel.write(__field_ref)?;\n";
    } else {
      out << "subparcel.write(&self.r#" << variable->GetName() << ")?;\n";
    }
    if (variable->IsNew() && ShouldForceDowngradeFor(CommunicationSide::WRITE)) {
      out.Dedent();
      out << "}\n";
    }
  }
  out << "Ok(())\n";
  out.Dedent();
  out << "})\n";
}

void GenerateParcelDeserializeBody(CodeWriter& out, const AidlStructuredParcelable* parcel,
                                   const AidlTypenames& typenames) {
  out << "parcel.sized_read(|subparcel| {\n";
  out.Indent();

  for (const auto& variable : parcel->GetFields()) {
    if (variable->IsNew() && ShouldForceDowngradeFor(CommunicationSide::READ)) {
      out << "if (false) {\n";
      out.Indent();
    }
    out << "if subparcel.has_more_data() {\n";
    out.Indent();
    if (TypeNeedsOption(variable->GetType(), typenames)) {
      out << "self.r#" << variable->GetName() << " = Some(subparcel.read()?);\n";
    } else {
      out << "self.r#" << variable->GetName() << " = subparcel.read()?;\n";
    }
    if (variable->IsNew() && ShouldForceDowngradeFor(CommunicationSide::READ)) {
      out.Dedent();
      out << "}\n";
    }
    out.Dedent();
    out << "}\n";
  }
  out << "Ok(())\n";
  out.Dedent();
  out << "})\n";
}

void GenerateParcelBody(CodeWriter& out, const AidlUnionDecl* parcel,
                        const AidlTypenames& typenames) {
  GenerateDeprecated(out, *parcel);
  auto alignment = cpp::AlignmentOfDefinedType(*parcel, typenames);
  if (parcel->IsFixedSize()) {
    AIDL_FATAL_IF(alignment == std::nullopt, *parcel);
    auto tag = std::to_string(*alignment * 8);
    // This repr may use a tag larger than u8 to make sure the tag padding takes into account that
    // the overall alignment is computed as if i64/f64 were always 8-byte aligned
    out << "#[repr(C, u" << tag << ", align(" << std::to_string(*alignment) << "))]\n";
  }
  out << "pub enum r#" << parcel->GetName() << " {\n";
  out.Indent();
  for (const auto& variable : parcel->GetFields()) {
    GenerateDeprecated(out, *variable);
    auto field_type =
        RustNameOf(variable->GetType(), typenames, StorageMode::PARCELABLE_FIELD, Lifetime::NONE);
    out << variable->GetCapitalizedName() << "(" << field_type << "),\n";
  }
  out.Dedent();
  out << "}\n";
  if (parcel->IsFixedSize()) {
    for (const auto& variable : parcel->GetFields()) {
      const auto& var_type = variable->GetType();
      std::string rust_type =
          RustNameOf(var_type, typenames, StorageMode::PARCELABLE_FIELD, Lifetime::NONE);
      // Assert the size of each enum variant's payload
      auto variable_size = cpp::SizeOf(var_type, typenames);
      AIDL_FATAL_IF(variable_size == std::nullopt, var_type);
      out << "static_assertions::const_assert_eq!(std::mem::size_of::<" << rust_type << ">(), "
          << std::to_string(*variable_size) << ");\n";
    }
    // Assert the alignment of the enum
    AIDL_FATAL_IF(alignment == std::nullopt, *parcel);
    out << "static_assertions::const_assert_eq!(std::mem::align_of::<" << parcel->GetName()
        << ">(), " << std::to_string(*alignment) << ");\n";

    // Assert the size of the enum, taking into the tag and its padding into account
    auto union_size = cpp::SizeOfDefinedType(*parcel, typenames);
    AIDL_FATAL_IF(union_size == std::nullopt, *parcel);
    out << "static_assertions::const_assert_eq!(std::mem::size_of::<" << parcel->GetName()
        << ">(), " << std::to_string(*union_size) << ");\n";
  }
}

void GenerateParcelDefault(CodeWriter& out, const AidlUnionDecl* parcel,
                           const AidlTypenames& typenames __attribute__((unused))) {
  out << "impl";
  WriteParams(out, parcel, ": Default");
  out << " Default for r#" << parcel->GetName();
  WriteParams(out, parcel);
  out << " {\n";
  out.Indent();
  out << "fn default() -> Self {\n";
  out.Indent();

  AIDL_FATAL_IF(parcel->GetFields().empty(), *parcel)
      << "Union '" << parcel->GetName() << "' is empty.";
  const auto& first_field = parcel->GetFields()[0];
  const auto& first_value = first_field->ValueString(ConstantValueDecorator);

  out << "Self::";
  if (first_field->GetDefaultValue()) {
    out << first_field->GetCapitalizedName() << "(" << first_value << ")\n";
  } else {
    out << first_field->GetCapitalizedName() << "(Default::default())\n";
  }

  out.Dedent();
  out << "}\n";
  out.Dedent();
  out << "}\n";
}

void GenerateParcelSerializeBody(CodeWriter& out, const AidlUnionDecl* parcel,
                                 const AidlTypenames& typenames) {
  out << "match self {\n";
  out.Indent();
  int tag = 0;
  for (const auto& variable : parcel->GetFields()) {
    out << "Self::" << variable->GetCapitalizedName() << "(v) => {\n";
    out.Indent();
    if (variable->IsNew() && ShouldForceDowngradeFor(CommunicationSide::WRITE)) {
      out << "if (true) {\n";
      out << "  Err(binder::StatusCode::BAD_VALUE)\n";
      out << "} else {\n";
      out.Indent();
    }
    out << "parcel.write(&" << std::to_string(tag++) << "i32)?;\n";
    if (TypeNeedsOption(variable->GetType(), typenames)) {
      out << "let __field_ref = v.as_ref().ok_or(binder::StatusCode::UNEXPECTED_NULL)?;\n";
      out << "parcel.write(__field_ref)\n";
    } else {
      out << "parcel.write(v)\n";
    }
    if (variable->IsNew() && ShouldForceDowngradeFor(CommunicationSide::WRITE)) {
      out.Dedent();
      out << "}\n";
    }
    out.Dedent();
    out << "}\n";
  }
  out.Dedent();
  out << "}\n";
}

void GenerateParcelDeserializeBody(CodeWriter& out, const AidlUnionDecl* parcel,
                                   const AidlTypenames& typenames) {
  out << "let tag: i32 = parcel.read()?;\n";
  out << "match tag {\n";
  out.Indent();
  int tag = 0;
  for (const auto& variable : parcel->GetFields()) {
    auto field_type =
        RustNameOf(variable->GetType(), typenames, StorageMode::PARCELABLE_FIELD, Lifetime::NONE);

    out << std::to_string(tag++) << " => {\n";
    out.Indent();
    if (variable->IsNew() && ShouldForceDowngradeFor(CommunicationSide::READ)) {
      out << "if (true) {\n";
      out << "  Err(binder::StatusCode::BAD_VALUE)\n";
      out << "} else {\n";
      out.Indent();
    }
    out << "let value: " << field_type << " = ";
    if (TypeNeedsOption(variable->GetType(), typenames)) {
      out << "Some(parcel.read()?);\n";
    } else {
      out << "parcel.read()?;\n";
    }
    out << "*self = Self::" << variable->GetCapitalizedName() << "(value);\n";
    out << "Ok(())\n";
    if (variable->IsNew() && ShouldForceDowngradeFor(CommunicationSide::READ)) {
      out.Dedent();
      out << "}\n";
    }
    out.Dedent();
    out << "}\n";
  }
  out << "_ => {\n";
  out << "  Err(binder::StatusCode::BAD_VALUE)\n";
  out << "}\n";
  out.Dedent();
  out << "}\n";
}

template <typename ParcelableType>
void GenerateParcelableTrait(CodeWriter& out, const ParcelableType* parcel,
                             const AidlTypenames& typenames) {
  out << "impl";
  WriteParams(out, parcel);
  out << " binder::Parcelable for r#" << parcel->GetName();
  WriteParams(out, parcel);
  out << " {\n";
  out.Indent();

  out << "fn write_to_parcel(&self, "
         "parcel: &mut binder::binder_impl::BorrowedParcel) -> std::result::Result<(), "
         "binder::StatusCode> "
         "{\n";
  out.Indent();
  GenerateParcelSerializeBody(out, parcel, typenames);
  out.Dedent();
  out << "}\n";

  out << "fn read_from_parcel(&mut self, "
         "parcel: &binder::binder_impl::BorrowedParcel) -> std::result::Result<(), "
         "binder::StatusCode> {\n";
  out.Indent();
  GenerateParcelDeserializeBody(out, parcel, typenames);
  out.Dedent();
  out << "}\n";

  out.Dedent();
  out << "}\n";

  // Emit the outer (de)serialization traits
  out << "binder::impl_serialize_for_parcelable!(r#" << parcel->GetName();
  WriteParams(out, parcel);
  out << ");\n";
  out << "binder::impl_deserialize_for_parcelable!(r#" << parcel->GetName();
  WriteParams(out, parcel);
  out << ");\n";
}

template <typename ParcelableType>
void GenerateMetadataTrait(CodeWriter& out, const ParcelableType* parcel) {
  out << "impl";
  WriteParams(out, parcel);
  out << " binder::binder_impl::ParcelableMetadata for r#" << parcel->GetName();
  WriteParams(out, parcel);
  out << " {\n";
  out.Indent();

  out << "fn get_descriptor() -> &'static str { \"" << parcel->GetCanonicalName() << "\" }\n";

  if (parcel->IsVintfStability()) {
    out << "fn get_stability(&self) -> binder::binder_impl::Stability { "
           "binder::binder_impl::Stability::Vintf }\n";
  }

  out.Dedent();
  out << "}\n";
}

template <typename ParcelableType>
void GenerateRustParcel(CodeWriter* code_writer, const ParcelableType* parcel,
                        const AidlTypenames& typenames) {
  vector<string> derives = parcel->RustDerive();

  // Debug is always derived because all Rust AIDL types implement it
  // ParcelFileDescriptor doesn't support any of the others because
  // it's a newtype over std::fs::File which only implements Debug
  derives.insert(derives.begin(), "Debug");

  *code_writer << "#[derive(" << Join(derives, ", ") << ")]\n";
  GenerateParcelBody(*code_writer, parcel, typenames);
  GenerateConstantDeclarations(*code_writer, *parcel, typenames);
  GenerateParcelDefault(*code_writer, parcel, typenames);
  GenerateParcelableTrait(*code_writer, parcel, typenames);
  GenerateMetadataTrait(*code_writer, parcel);
}

void GenerateRustEnumDeclaration(CodeWriter* code_writer, const AidlEnumDeclaration* enum_decl,
                                 const AidlTypenames& typenames) {
  const auto& aidl_backing_type = enum_decl->GetBackingType();
  auto backing_type = RustNameOf(aidl_backing_type, typenames, StorageMode::VALUE, Lifetime::NONE);

  *code_writer << "#![allow(non_upper_case_globals)]\n";
  *code_writer << "use binder::declare_binder_enum;\n";
  *code_writer << "declare_binder_enum! {\n";
  code_writer->Indent();

  GenerateDeprecated(*code_writer, *enum_decl);
  auto alignment = cpp::AlignmentOf(aidl_backing_type, typenames);
  AIDL_FATAL_IF(alignment == std::nullopt, *enum_decl);
  // u64 is aligned to 4 bytes on x86 which may underalign the whole struct if it's the backing type
  // so we need to set the alignment manually as if u64 were aligned to 8 bytes.
  *code_writer << "#[repr(C, align(" << std::to_string(*alignment) << "))]\n";
  *code_writer << "r#" << enum_decl->GetName() << " : [" << backing_type << "; "
               << std::to_string(enum_decl->GetEnumerators().size()) << "] {\n";
  code_writer->Indent();
  for (const auto& enumerator : enum_decl->GetEnumerators()) {
    auto value = enumerator->GetValue()->ValueString(aidl_backing_type, ConstantValueDecorator);
    GenerateDeprecated(*code_writer, *enumerator);
    *code_writer << "r#" << enumerator->GetName() << " = " << value << ",\n";
  }
  code_writer->Dedent();
  *code_writer << "}\n";

  code_writer->Dedent();
  *code_writer << "}\n";
}

void GenerateClass(CodeWriter* code_writer, const AidlDefinedType& defined_type,
                   const AidlTypenames& types, const Options& options) {
  if (const AidlStructuredParcelable* parcelable = defined_type.AsStructuredParcelable();
      parcelable != nullptr) {
    GenerateRustParcel(code_writer, parcelable, types);
  } else if (const AidlEnumDeclaration* enum_decl = defined_type.AsEnumDeclaration();
             enum_decl != nullptr) {
    GenerateRustEnumDeclaration(code_writer, enum_decl, types);
  } else if (const AidlInterface* interface = defined_type.AsInterface(); interface != nullptr) {
    GenerateRustInterface(code_writer, interface, types, options);
  } else if (const AidlUnionDecl* union_decl = defined_type.AsUnionDeclaration();
             union_decl != nullptr) {
    GenerateRustParcel(code_writer, union_decl, types);
  } else {
    AIDL_FATAL(defined_type) << "Unrecognized type sent for Rust generation.";
  }

  for (const auto& nested : defined_type.GetNestedTypes()) {
    (*code_writer) << "pub mod r#" << nested->GetName() << " {\n";
    code_writer->Indent();
    GenerateClass(code_writer, *nested, types, options);
    code_writer->Dedent();
    (*code_writer) << "}\n";
  }
}

void GenerateRust(const string& filename, const Options& options, const AidlTypenames& types,
                  const AidlDefinedType& defined_type, const IoDelegate& io_delegate) {
  CodeWriterPtr code_writer = io_delegate.GetCodeWriter(filename);

  GenerateAutoGenHeader(*code_writer, options);

  // Forbid the use of unsafe in auto-generated code.
  // Unsafe code should only be allowed in libbinder_rs.
  *code_writer << "#![forbid(unsafe_code)]\n";
  // Disable rustfmt on auto-generated files, including the golden outputs
  *code_writer << "#![cfg_attr(rustfmt, rustfmt_skip)]\n";
  GenerateClass(code_writer.get(), defined_type, types, options);
  GenerateMangledAliases(*code_writer, defined_type);

  AIDL_FATAL_IF(!code_writer->Close(), defined_type) << "I/O Error!";
}

}  // namespace rust
}  // namespace aidl
}  // namespace android