Dart - dill文件序列化为可读文本（续）

喜欢ヅ旅行 2024-05-24 21:40 7阅读 0赞

#### 文章目录 ####

*  前言
 *  开发环境
 *  app.dill文件
 *  DEPS文件
 *  最后

--------------------

## 前言 ##

对前文[Dart - dill文件序列化为可读文本][Dart - dill]做一些补充。

## 开发环境 ##

*  macOS: 13.4
 *  Dart: 3.0.5
 *  Flutter: 3.10.5

## app.dill文件 ##

因为Flutter项目编译后会自动生成`app.dill`文件（位于项目根目录下的`.dart_tool/flutter_build/xxx/app.dill`路径），同时自动生成的`app.dill`文件能正常序列化为文本，所以不手动生成是没问题的。如果非要按照以下命令手动生成`app.dill`文件：

dart compile kernel lib/main.dart --output lib/app.dill

一般会报这样的错：

/xxx/flutter/packages/flutter/lib/src/material/animated_icons.dart:9:8: Error: Dart library 'dart:ui' is not available on this platform.
    import 'dart:ui' as ui show Canvas, Paint, Path;
           ^
    Context: The unavailable library 'dart:ui' is imported through these packages:
    
        package:untitled => package:flutter => dart:ui
        ...
    
    Detailed import paths for (some of) the these imports:
    
        package:untitled/main.dart => package:flutter/material.dart => package:flutter/src/material/about.dart => package:flutter/foundation.dart => package:flutter/src/foundation/assertions.dart => package:flutter/src/foundation/diagnostics.dart => package:flutter/src/foundation/debug.dart => dart:ui
        ...

从报错信息看，似乎是因为使用了Flutter相关的库导致的。执行`dart compile kernel -h`命令看输出结果也没几个参数可以设置，难道Flutter编译项目时用的是其他命令？

在Flutter项目根目录路径下执行运行命令：

flutter run -v

`-v`参数的作用是打印执行命令过程中的日志。虽然日志很长，但是可以用`app.dill`为关键词搜索找到关键日志：

[   +1 ms] /xxx/flutter/bin/cache/dart-sdk/bin/dart --disable-dart-dev
    /xxx/flutter/bin/cache/dart-sdk/bin/snapshots/frontend_server.dart.snapshot --sdk-root
    /xxx/flutter/bin/cache/artifacts/engine/common/flutter_patched_sdk/ --incremental --target=flutter --experimental-emit-debug-metadata
    -DFLUTTER_WEB_AUTO_DETECT=true -DFLUTTER_WEB_CANVASKIT_URL=https://www.gstatic.com/flutter-canvaskit/45f6e009110df4f34ec2cf99f63cf73b71b7a420/ --output-dill
    /var/folders/_p/n8w3bslx2qg8sh057tm1hcmw0000gn/T/flutter_tools.pCnbY1/flutter_tool.BWP10J/app.dill --packages /xxx/untitled/.dart_tool/package_config.json
    -Ddart.vm.profile=false -Ddart.vm.product=false --enable-asserts --track-widget-creation --filesystem-scheme org-dartlang-root --initialize-from-dill
    build/4d25a1cda3833f76c80232d3b1a3704b.cache.dill.track.dill --verbosity=error --enable-experiment=alternative-invalidation-strategy

咦？竟然用的是`frontend_server.dart.snapshot`，这是Dart前端编译的快照文件。相比于`dart compile kernel`命令，可设置的参数就丰富多了。实测必须要指定的关键参数有两个，分别是`--sdk-root`和`--target`：

*  `--sdk-root`

指定SDK根路径，如果不设置会报一堆关于找不到库的错误，虽然最后能生成`dill`文件，但是序列化为文本后会出现很多`Problems in library`：

![screenshot1][]

*  `--target`

参数用于确定可用核心库的目标模型，默认是`vm`，必须设置为`flutter`。如果不设置会报这样的错：

Unhandled exception:
    Null check operator used on a null value
    #0      DillLoader.read (package:front_end/src/fasta/dill/dill_loader.dart:123:38)
    #1      DillTarget.loadExtraRequiredLibraries (package:front_end/src/fasta/dill/dill_target.dart:60:14)
    #2      DillLoader.read (package:front_end/src/fasta/dill/dill_loader.dart:138:16)
    #3      DillLoader.appendLibraries (package:front_end/src/fasta/dill/dill_loader.dart:290:18)
    #4      generateKernelInternal.<anonymous closure> (package:front_end/src/kernel_generator_impl.dart:84:27)
    <asynchronous suspension>
    #5      withCrashReporting (package:front_end/src/fasta/crash.dart:136:12)
    <asynchronous suspension>
    #6      kernelForProgramInternal.<anonymous closure> (package:front_end/src/api_prototype/kernel_generator.dart:62:29)
    <asynchronous suspension>
    #7      kernelForProgramInternal (package:front_end/src/api_prototype/kernel_generator.dart:61:10)
    <asynchronous suspension>
    #8      kernelForProgram (package:front_end/src/api_prototype/kernel_generator.dart:50:11)
    <asynchronous suspension>
    #9      compileToKernel (package:vm/kernel_front_end.dart:452:22)
    <asynchronous suspension>
    #10     FrontendCompiler.compile (package:frontend_server/frontend_server.dart:620:17)
    <asynchronous suspension>
    #11     starter (package:frontend_server/starter.dart:99:12)
    <asynchronous suspension>
    #12     main (file:///opt/s/w/ir/x/w/sdk/pkg/frontend_server/bin/frontend_server_starter.dart:13:14)
    <asynchronous suspension>

最终得到的可用命令：

dart /xxx/flutter/bin/cache/dart-sdk/bin/snapshots/frontend_server.dart.snapshot --sdk-root /xxx/flutter/bin/cache/artifacts/engine/common/flutter_patched_sdk/ --target=flutter xxx.dart --output-dill xxx.dill

请根据实际需要替换命令中的Flutter SDK等路径。由于参数有所精简，所以用以上命令生成的`app.dill`文件（左侧）和Flutter编译自动生成的`app.dill`文件（右侧）有所差异，不过差别不大：

![screenshot2][]

## DEPS文件 ##

前文中提到了`DEPS`文件，和`pubspec.yaml`文件相比，除了指定了项目的依赖项，还配置了`hook`用于在`.dart_tool`目录下生成`package_config.json`文件，而`pubspec.yaml`文件只是配置文件，`package_config.json`文件的生成需要借助`dart pub get`命令。

打开Dart SDK目录下的`sdk/DEPS`文件，脚本拉到最后面就是`hook`数组：

hooks = [
      {
        
        # Generate the .dart_tool/package_confg.json file.
        'name': 'Generate .dart_tool/package_confg.json',
        'pattern': '.',
        'action': ['python3', 'sdk/tools/generate_package_config.py'],
      },
      ...
    ]

当用于同步依赖项的`gclient sync`命令执行结束后会执行这些`hook`。首个`hook`就是用于生成`package_confg.json`文件，执行的是`generate_package_config.py`脚本，最终执行到位于同目录下的`generate_package_config.dart`文件。

## 最后 ##

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[Dart - dill]: https://blog.csdn.net/crasowas/article/details/131623479
[screenshot1]: https://image.dandelioncloud.cn/pgy_files/images/2024/05/24/4185decd40334dc1a88af455057f02e8.png
[screenshot2]: https://image.dandelioncloud.cn/pgy_files/images/2024/05/24/209796eb65d8453f83f761baf86a3b77.png