Flutter源碼剖析(一):源碼獲取與構建

時間 2020-11-02

標籤 java python android ios git github shell json vim xcode 欄目 Java 简体版

原文原文鏈接

概述

本文介紹了Flutter源碼的獲取與構建，後面會另有文章介紹Flutter源碼的版本管理、開發環境搭建等主題。java

準備工做

Flutter源碼分爲兩個部分：python

flutter/flutter是框架層，爲開發者提供各類接口，主要是dart代碼。
flutter/engine是引擎層，負責Flutter的渲染以及宿主的交互。

相關依賴的安裝可參考官方文檔：Setting up the Engine development environment · flutter/flutter Wiki。以個人Mac爲例，如JDK等通常都已經安裝，無需擔憂。android

源碼下載

flutter/flutter能夠直接經過git下載，可是flutter/engine須要經過gclient工具獲取，由於engine有不少依賴，gclient能夠很好地處理這些依賴，簡化源碼管理流程。ios

首先，新建一個目錄，下載flutter框架代碼：git

$ mkdir flutter_source_code
$ cd flutter_source_code
$ git clone https://github.com/flutter/flutter.git
Cloning into 'flutter'...
remote: Enumerating objects: 12, done.
remote: Counting objects: 100% (12/12), done.
remote: Compressing objects: 100% (12/12), done.
remote: Total 272396 (delta 0), reused 6 (delta 0), pack-reused 272384
Receiving objects: 100% (272396/272396), 116.98 MiB | 2.48 MiB/s, done.
Resolving deltas: 100% (210440/210440), done.

獲取depot_tools工具（這個一開始是用來管理chromium源碼的）：github

$ git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
Cloning into 'depot_tools'...
remote: Sending approximately 34.14 MiB ...
remote: Total 40539 (delta 27803), reused 40539 (delta 27803)
Receiving objects: 100% (40539/40539), 34.14 MiB | 5.04 MiB/s, done.
Resolving deltas: 100% (27803/27803), done.

設置環境變量（每次構建以前都要設置，也能夠寫入系統配置）：shell

export PATH=$PATH:`pwd`/depot_tools

開始拉取代碼（這一步比較耗時）json

$ gclient sync                                                                                               [18:04:43] 

......

remote: Enumerating objects: 25, done. 
remote: Counting objects: 100% (25/25), done.
remote: Compressing objects: 100% (22/22), done.
remote: Total 209672 (delta 10), reused 13 (delta 3), pack-reused 209647
Receiving objects: 100% (209672/209672), 196.61 MiB | 3.74 MiB/s, done.
Resolving deltas: 100% (153791/153791), done.
Syncing projects:  31% (33/104) src/third_party/vulkan
[0:03:59] Still working on:
[0:03:59]   src/ios_tools
[0:03:59]   src/third_party/angle
[0:03:59]   src/third_party/dart
[0:03:59]   src/third_party/icu

......

[0:12:48] Still working on:
[0:12:48]   src/third_party/dart

Syncing projects: 100% (104/104), done.
Running hooks: 100% ( 9/ 9) dart package config
________ running 'vpython src/flutter/tools/run_third_party_dart.py' in '/Users/vimerzhao/WorkProject/flutter_source_code'
Resolving dependencies... (1.7s)
+ charcode 1.1.3
+ collection 1.14.13
+ meta 1.2.3
+ package_config 1.9.3
+ path 1.7.0
+ pub_semver 1.4.4
+ source_span 1.7.0
+ string_scanner 1.0.5
+ term_glyph 1.1.0
+ yaml 2.2.1
Changed 10 dependencies!

須要注意的是，Syncing projects: 100% (104/104), done以後，會繼續下載一些大文件，可能命令行沒有輸出，必定不能強制退出，能夠經過資源管理器查看網絡的流量，肯定cipd是否在下載：vim

（由於git不是很擅長下載大文件，因此產生了cipd這個程序來作這些工做）xcode

此時的目錄結構：

$ tree -L 1
.
├── depot_tools # 源碼管理工具
├── flutter     # flutter framework目錄
└── src         # flutter engine以及相關依賴所在目錄

framework的版本和engine的版本是一一對應的，framework的分支規則以下：

stable是當前的穩定分支，無特殊狀況，推薦開發者使用該分支做爲flutter sdk
master包含最新的特性，可是不穩定
每一個版本會打上對應的tag

截止到 2020-10-29 ,最新的較穩定版本是 1.22.0，因而咱們也先切到這個版本（不是必選的，可是我的認爲：基於一個明確的版本編譯和修改源代碼彷佛更合適）。

$ cd flutter
$ git checkout 1.22.0
$ cat bin/internal/engine.version
5babba6c4d25fa237bbf755ab85c9a0c50b3c6ec

engine.version這個文件指定了framework對應的engine版本，接下來，咱們進入engine目錄切換到此次commit。

$ cd ../src/flutter
$ git reset --hard 5babba6c4d25fa237bbf755ab85c9a0c50b3c6ec
HEAD is now at 5babba6c4 Flutter 1.22.0-12.3.pre engine cherrypicks (#21466)

此時，咱們須要執行如下命令：

$ gclient sync --with_branch_heads --with_tags
Syncing projects: 100% (104/104), done.
......
Running hooks: 100% ( 8/ 8) dart package config
......
Running hooks: 100% (8/8), done.

後面這兩個參數的含義比較晦澀，參考Chromium的說明，其含義是：

Checkout all the submodules at their branch DEPS revisions

由於切換分支以後，某些依賴的版本可能有更改，因此須要再次sync一下，直接在src/flutter目錄執行便可。

以上就完成了源碼環境的搭建，下面正式開始編譯。

源碼編譯

首先咱們退回到src目錄，而後經過gn生成ninja須要的元數據：

$ cd ..
$ pwd
/Users/vimerzhao/WorkProject/flutter_source_code/src
$ ./flutter/tools/gn --unoptimized --android --runtime-mode debug --android-cpu arm
Generating GN files in: out/android_debug_unopt
Generating Xcode projects took 75ms
Done. Made 438 targets from 197 files in 1960ms

對於編譯參數，Compiling the engine · flutter/flutter Wiki有詳細介紹，在此不作贅述，這裏我構建的是一個未優化、Android平臺、debug版本、arm 32位的 engine。

此時，查看out目錄，能夠看到：

$ ls out/
android_debug_unopt   compile_commands.json

compile_commands.json能夠做爲IDE的索引文件，提供類/函數/變量的跳轉等能力，後面會說到。

而後就能夠開始正式的編譯了：

$ ninja -C out/android_debug_unopt
ninja: Entering directory `out/android_debug_unopt'
[38/3844] ACTION //flutter/shell/platform/android:flutter_shell_java(//build/toolchain/android:clang_arm)
警告: ../../third_party/android_tools/sdk/build-tools/30.0.1/core-lambda-stubs.jar(java/lang/invoke/LambdaMetafactory.class): 主版本 53 比 52 新, 此編譯器
支持最新的主版本。
  建議升級此編譯器。
注: 某些輸入文件使用或覆蓋了已過期的 API。
注: 有關詳細信息, 請使用 -Xlint:deprecation 從新編譯。
1 個警告
[3844/3844] STAMP obj/default.stamp

$ ls out/android_debug_unopt                                                                 [19:35:15]
all.xcodeproj                                 flutter_embedding_debug-sources.jar.md5.stamp lib.stripped
args.gn                                       flutter_embedding_debug.jar                   libflutter.so
armeabi_v7a_debug.jar                         flutter_embedding_debug.jar.md5.stamp         libflutter.so.TOC
armeabi_v7a_debug.pom                         flutter_embedding_debug.pom                   obj
build.ninja                                   flutter_icu                                   toolchain.ninja
build.ninja.d                                 flutter_patched_sdk                           vm_outline_strong.dill
clang_x64                                     gen                                           vm_platform_strong.dill
flutter.jar                                   gyp-mac-tool                                  vm_platform_strong.dill.d
flutter_embedding_debug-sources.jar           icudtl.dat                                    zip_archives

其中，flutter_embedding_debug.jar是Android嵌入層代碼，libflutter.so是flutter的引擎層代碼，經過這兩個文件，能夠在Android工程混合接入Flutter代碼。

源碼使用

建立一個工程：

$ pwd
/Users/vimerzhao/WorkProject/flutter_source_code
$ ls
depot_tools flutter     src
$ ./flutter/bin/flutter create flutter_demo
Downloading Dart SDK from Flutter engine 5babba6c4d25fa237bbf755ab85c9a0c50b3c6ec...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  172M  100  172M    0     0  4381k      0  0:00:40  0:00:40 --:--:-- 4723k
Building flutter tool...
Downloading Material fonts...                                       0.5s
Downloading Gradle Wrapper...                                       0.1s
Downloading package sky_engine...                                   0.3s
Downloading flutter_patched_sdk tools...                            2.7s
Downloading flutter_patched_sdk_product tools...                    2.1s
Downloading darwin-x64 tools...                                     8.2s
Downloading libimobiledevice...                                     0.0s
Downloading usbmuxd...                                              0.7s
Downloading libplist...                                             0.0s
Downloading openssl...                                              0.2s

......
Creating project flutter_demo...
  flutter_demo/ios/Runner.xcworkspace/contents.xcworkspacedata (created)
  flutter_demo/ios/Runner.xcworkspace/xcshareddata/IDEWorkspaceChecks.plist (created)

  ......

  flutter_demo/.idea/runConfigurations/main_dart.xml (created)
  flutter_demo/.idea/libraries/Dart_SDK.xml (created)
  flutter_demo/.idea/libraries/KotlinJavaRuntime.xml (created)
  flutter_demo/.idea/modules.xml (created)
  flutter_demo/.idea/workspace.xml (created)
Running "flutter pub get" in flutter_demo...                        2.3s
Wrote 71 files.

All done!

......

Run "flutter doctor" for information about installing additional components.

In order to run your application, type:

  $ cd flutter_demo
  $ flutter run

使用flutter並指定本地engine運行（不指定則會拉遠程的、已經構建好的engine）。

$ ../flutter/bin/flutter run --local-engine-src-path ~/WorkProject/flutter_source_code/src --local-engine=android_debug_unopt
No Flutter engine build found at /Users/vimerzhao/WorkProject/flutter_source_code/src/out/host_debug_unopt.

$ ../flutter/bin/flutter run --local-engine-src-path ~/WorkProject/flutter_source_code/src --local-engine=host_debug_unopt
Launching lib/main.dart on DUK AL20 in debug mode...
Oops; flutter has exited unexpectedly: "Invalid argument(s): Cannot find executable for
/Users/vimerzhao/WorkProject/flutter_source_code/src/out/host_debug_unopt/dart-sdk/bin/dart.".
A crash report has been written to /Users/vimerzhao/WorkProject/flutter_source_code/flutter_demo/flutter_02.log.
...
FAILURE: Build failed with an exception
* Where:
Script '/Users/vimerzhao/WorkProject/flutter_source_code/flutter/packages/flutter_tools/gradle/flutter.gradle' line: 904
* What went wrong:
Execution failed for task ':app:compileFlutterBuildDebug'.
> Process 'command '/Users/vimerzhao/WorkProject/flutter_source_code/flutter/bin/flutter'' finished with non-zero exit value 1
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 1s
Running Gradle task 'assembleDebug'...
Running Gradle task 'assembleDebug'... Done 1.8s
https://git.io/JTDf0

$../flutter/bin/flutter run --local-engine-src-path ~/WorkProject/flutter_source_code/src --local-engine=h
ost_debug_unopt
Launching lib/main.dart on DUK AL20 in debug mode...
Error: Error when reading '../src/out/host_debug_unopt/gen/frontend_server.dart.snapshot': No such file or directory
the Dart compiler exited unexpectedly.
the Dart compiler exited unexpectedly.
Running Gradle task 'assembleDebug'...

總的來講，遇到一些官方文檔上沒有提到的問題：

輸入android_debug_unopt 卻提示找不到 host_debug_unopt，這個莫名其妙，只能先改一下以前構建的文件夾名稱了。
找不到dart-sdk，flutter會下載到bin/cache目錄，只能本身手動copy一份到報錯的目錄。
找不到frontend_server.dart.snapshot，在flutter目錄用find . -name "frontend_server.dart.snapshot"找到，而後手動copy一份。

解決這三個問題以後，終於能夠運行了。

$ ../flutter/bin/flutter run --local-engine-src-path ~/WorkProject/flutter_source_code/src --local-engine=host_debug_unopt
Launching lib/main.dart on DUK AL20 in debug mode...
Running Gradle task 'assembleDebug'...
Running Gradle task 'assembleDebug'... Done                        18.1s
✓ Built build/app/outputs/flutter-apk/app-debug.apk.
Installing build/app/outputs/flutter-apk/app.apk...                 3.5s
Waiting for DUK AL20 to report its views...                          8ms
Syncing files to device DUK AL20...                                210ms
Flutter run key commands.
r Hot reload. 🔥🔥🔥
R Hot restart.
h Repeat this help message.
d Detach (terminate "flutter run" but leave application running).
c Clear the screen
q Quit (terminate the application on the device).
An Observatory debugger and profiler on DUK AL20 is available at: http://127.0.0.1:63146/LE7Uc6cshds=/
D/AwareBitmapCacher(24977): handleInit switch not opened pid=24977

Application finished.