pkg/vm/bin/protobuf_aware_treeshaker.dart

#!/usr/bin/env dart
// Copyright (c) 2019, 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.

/// This program will take a .dill file and do a protobuf aware tree-shaking.
///
/// All fields of GeneratedMessage subclasses that are not accessed with their
/// getter or setter will have their metadata removed from the class definition.
///
/// Then a general treeshaking will be run, and
/// all GeneratedMessage subclasses that are never used directly will be
/// removed.
///
/// The processed program will have observable differences: The tree-shaken
/// fields will be parsed as unknown fields.
/// The toString method will treat the unknown fields as missing.
///
/// Using the `GeneratedMessage.info_` field to reflect on fields will have
/// unpredictable behavior.
///
/// Constants are evaluated, this is mainly to enable detecting
/// `@pragma('vm:entry-point')`.
library vm.protobuf_aware_treeshaker;

import 'dart:async';
import 'dart:io';
import 'dart:typed_data';

import 'package:args/args.dart';
import 'package:kernel/binary/ast_to_binary.dart';
import 'package:kernel/core_types.dart' show CoreTypes;
import 'package:kernel/kernel.dart';
import 'package:kernel/target/targets.dart' show TargetFlags, getTarget;
import 'package:vm/kernel_front_end.dart'
    show runGlobalTransformations, ErrorDetector, KernelCompilationArguments;
import 'package:vm/modular/target/install.dart' show installAdditionalTargets;
import 'package:vm/transformations/type_flow/transformer.dart'
    as globalTypeFlow
    show transformComponent;

ArgResults parseArgs(List<String> args) {
  ArgParser argParser =
      ArgParser()
        ..addOption(
          'platform',
          valueHelp: "path/to/vm_platform.dill",
          help:
              'A platform.dill file to append to the input. If not given, no '
              'platform.dill will be appended.',
        )
        ..addOption(
          'target',
          allowed: ['dart_runner', 'flutter', 'flutter-runner', 'vm'],
          defaultsTo: 'vm',
          help: 'Target platform.',
        )
        ..addFlag(
          'aot',
          help:
              'If set, produces kernel file for AOT compilation (enables '
              'global transformations). Otherwise, writes regular dill.',
          defaultsTo: false,
        )
        ..addFlag(
          'write-txt',
          help: 'Also write the result in kernel-text format as <out.dill>.txt',
          defaultsTo: false,
        )
        ..addFlag(
          'remove-core-libs',
          help:
              'If set, the output dill file will not include `dart:` libraries',
          defaultsTo: false,
        )
        ..addMultiOption(
          'define',
          abbr: 'D',
          help: 'Perform constant evaluation with this environment define set.',
          valueHelp: 'variable=value',
        )
        ..addFlag(
          'remove-source',
          help: 'Removes source code from the emitted dill',
          defaultsTo: false,
        )
        ..addFlag(
          'verbose',
          help: 'Write to stdout about what classes and fields where removed',
        )
        ..addFlag('help', help: 'Prints this help', negatable: false);

  ArgResults? argResults;
  try {
    argResults = argParser.parse(args);
  } on FormatException catch (e) {
    print(e.message);
  }

  if (argResults == null || argResults['help'] || argResults.rest.length != 2) {
    String script = 'protobuf_aware_treeshaker.dart';
    print(
      'A tool for removing protobuf messages types that are never referred by a program',
    );
    print('Usage: $script [args] <input.dill> <output.dill>');

    print(argParser.usage);
    exit(-1);
  }

  if (argResults['aot'] && argResults['remove-core-libs']) {
    print('The `--aot` option is incompatible with `--remove-core-libs`');
    exit(-1);
  }

  return argResults;
}

Future main(List<String> args) async {
  ArgResults argResults = parseArgs(args);

  final input = argResults.rest[0];
  final output = argResults.rest[1];

  var bytes = File(input).readAsBytesSync();
  final platformFile = argResults['platform'];
  if (platformFile != null) {
    bytes = concatenate(File(platformFile).readAsBytesSync(), bytes);
  }
  final component = loadComponentFromBytes(bytes);

  installAdditionalTargets();

  final target = getTarget(argResults['target'], TargetFlags())!;

  // The [component] is treeshaken and has TFA annotations. Write output.
  if (argResults['aot']) {
    final nopErrorDetector = ErrorDetector();
    runGlobalTransformations(
      target,
      component,
      nopErrorDetector,
      KernelCompilationArguments(
        useGlobalTypeFlowAnalysis: true,
        enableAsserts: false,
        useProtobufTreeShakerV2: true,
      ),
    );
  } else {
    globalTypeFlow.transformComponent(
      target,
      CoreTypes(component),
      component,
      treeShakeProtobufs: true,
      treeShakeSignatures: false,
    );
  }

  if (argResults['aot']) {
    // Write kernel file for AOT compilation.
    final sink = File(output).openWrite();
    final printer = BinaryPrinter(sink);
    printer.writeComponentFile(component);
    await sink.close();
  } else {
    // Clean out the AOT-only TFA annotations and write regular dill.
    component.metadata.clear();
    await writeComponent(
      component,
      output,
      removeCoreLibs: argResults['remove-core-libs'],
      removeSource: argResults['remove-source'],
    );
  }
  if (argResults['write-txt']) {
    writeComponentToText(component, path: output + '.txt');
  }
}

Uint8List concatenate(Uint8List a, Uint8List b) {
  final bytes = Uint8List(a.length + b.length);
  bytes.setRange(0, a.length, a);
  bytes.setRange(a.length, a.length + b.length, b);
  return bytes;
}

Future writeComponent(
  Component component,
  String filename, {
  required bool removeCoreLibs,
  required bool removeSource,
}) async {
  if (removeSource) {
    component.uriToSource.clear();
  }

  for (final lib in component.libraries) {
    lib.dependencies.clear();
    lib.additionalExports.clear();
    lib.parts.clear();
  }

  final sink = File(filename).openWrite();
  final printer = BinaryPrinter(
    sink,
    libraryFilter: (lib) {
      if (removeCoreLibs && isCoreLibrary(lib)) return false;
      if (isLibEmpty(lib)) return false;
      return true;
    },
    includeSources: !removeSource,
  );

  printer.writeComponentFile(component);
  await sink.close();
}

bool isLibEmpty(Library lib) {
  return lib.classes.isEmpty &&
      lib.procedures.isEmpty &&
      lib.fields.isEmpty &&
      lib.typedefs.isEmpty &&
      lib.annotations.isEmpty;
}

bool isCoreLibrary(Library library) {
  return library.importUri.isScheme('dart');
}