关于BUCK
BUCK是Facebook开源的快速打包工具，可以用于多种语言及平台的项目打包，例如：C、C++、Java、iOS、Android等等。用于大型的iOS、Android项目，可以显著提升打包效率。
关于BUCK介绍的一些链接如下：
BUCK官网
What Makes Buck so Fast?：介绍了BUCK如何做到性能提升
BUCK源码： 里面有源码和大量Unit Test提供了很多示例，同时查看Issues可以找到很多问题的解决方案
iOS快速编译BUCK
基于Facebook Buck改造Android构建系统之初体验
核心概念
Build Rule
A build rule is a procedure for producing an output file from a set of input files.
Build Target
A build target is a string that is used to identify a build rule in your project.
Build File
A build file is a file named BUCK that defines one or more build rules.
.buckconfig
.buckconfig.
iOS打包相关Rule
| Rule | 产出 | 作用 |
|---|---|---|
| apple_asset_catalog() | 没有特定产出，可以作为apple_bundle()的依赖 | Contains resources stored in Apple asset catalog directories |
| apple_binary() | 静态库：.a file | An apple_binary() rule builds a native executable from the supplied set of Objective-C/C++ source files |
| apple_bundle() | .app 或者 .appex (apple watch extension) | An apple_bundle() rule takes an Apple binary and all of the resources and asset catalogs in the rule's transitive dependencies and generates a bundle containing all of those files. |
| apple_library() | 静态库：.a file | An apple_library() rule represents a set of Objective-C/C++ source files |
| apple_package() | ipa file | An apple_package() rule takes the output of an apple_bundle() rule and compresses it in an IPA (iOS App Store Package) file. |
| apple_resource() | This rule does not have any output on its own and can be built only as a dependency (either direct or transitive) of an apple_bundle() rule. | An apple_resource() rule contains sets of resource directories, files and file variants that can be bundled in an application bundle. |
| apple_test() | 无 | An apple_test() rule contains Objective-C/C++ code which can be built and used to test code contained in other rules. |
| core_data_model() | This rule does not have any output on its own and can be built only as a dependency (either direct or transitive) of an apple_bundle() rule, in which case all core_data_model() rules that the bundle rule depends on are merged and placed into the final output bundle together. | An core_data_model() rule contains models for Apple's Core Data framework. |
| prebuilt_apple_framework() | 无 | 引用.framework库 |
使用BUCK用于iOS工程打包
目录组织结构
对于一个多个子工程组成，通过依赖关系最终集成为单个可执行文件。使用BUCK，需要为每一个子工程都创建BUCK文件，在根目录配置.buckconfig。大致目录结构如下：
|—.buckconfig
|—BUCK
|—SubProject1
|---------src
|---------BUCK
|—SubProject2
|---------src
|---------BUCK
|—SubProject3
|---------src
|---------BUCK
|—SubProject4
|---------src
|---------BUCK
......
每个子工程的BUCK文件，负责配置build rule，生成静态.a 文件，然后最终通过根目录中的BUCK，来生成.ipa文件。
.buckconfig配置
[cache]mode = dir[cxx]cflags = -std=gnu11cxxflags = -std=c++14 -stdlib=libc++default_platform = iphonesimulator-x86_64combined_preprocess_and_compile = true[alias]SubProject1 = //SubProject1: SubProject1LibSubProject2 = //SubProject2: SubProject2LibSubProject3 = //SubProject3: SubProject3LibSubProject4 = //SubProject4: SubProject4Lib [apple]xctool_zip_target = //third-party/ios/xctool:xctool-minimal-zip [project]ignore = .buckd, \.hg, \.git, \.idea, \buck-cache, \buck-out, \
cxx：定义了一些C++编译的参数
alias: 定义了一些build target的别名。例如CTFoundation为例，在CTFoundation中的BUCK文件中定义了CTFoundationLib的rule，所以如果要打包CTFoundation，可以通过别名的方式，命令如下：
# 未用别名 buck build //SubProject1:SubProject1Lib # 使用别名 buck build SubProject1
apple: 指定了xctool的文件地址。Buck的iOS打包是依赖于xctool，所以需要把xctool的相关代码引入，具体内容可以参考示例：
git clone git@github.com:fbsamples/bucksamples.git cd bucksamples/cross-platform-scale-2015-demo/
BUCK文件配置
独立子工程的BUCK配置
下面以一个独立的子工程作为示例，而且没有其他依赖，所以可以作为第一个示例。它的BUCK文件配置如下：
apple_library(name = 'SubProject1Lib',preprocessor_flags = ['-fobjc-arc','-Wno-deprecated-declarations','-fmodules'],compiler_flags = ['-Wno-objc-designated-initializers','-fembed-bitcode'],linker_flags = ['-F$DEVELOPER_DIR/Platforms/iPhoneSimulator.platform/Developer/Library/PrivateFrameworks','-F$DEVELOPER_DIR/../SharedFrameworks','-F$DEVELOPER_DIR/Library/PrivateFrameworks',],srcs = glob(['src/**/**/**/*.m',]),frameworks = ['$SDKROOT/System/Library/Frameworks/Foundation.framework',],exported_headers = {'xxx1.h': './src/xxx.h','xxx2.h': './src/xxx2.h',...},#header_namespace = '',visibility = ['PUBLIC',], )
整个BUCK文件就一个apple_library，产出libCTLocation.a文件。可以看到里面可以指定一下编译的flags、依赖的framework、源代码、对外暴露的头文件等等。
通过命令 buck build CTLocation就可以打包查看，在buck-out目录中可以看到生成出来的.a文件。
需要注意的exported_headers的配置：
The set of header files that are made available for inclusion to the source files in this target and all targets that transitively depend on this one. These should be specified as either a list of header files or a dictionary of header names to header files. The header names can contain forward slashes (/). If a list of header files is specified, the headers can be imported with #import "$HEADER_PATH_PREFIX/$HEADER_NAME" or, if a header file that belongs to the same rule is being imported, with #import "$HEADER_NAME", where $HEADER_PATH_PREFIX is the value of the target's header_path_prefix attribute, and $HEADER_NAME is the filename of the header file. If a dictionary is specified, each header can be imported with #import "$HEADER_NAME", where $HEADER_NAME is the key corresponding to this file. In this case, the header_path_prefix attribute is ignored. In either case, quotes in the import statements can be replaced with angle brackets.
可以有两种配置格式，数组和字典。
使用数组的时候，其他代码引用是需要加上前缀例如：#import "SubProject1/xxx.h"，默认前缀和apple_library的name一致，可以通过设置header_path_prefix改变。
使用字典的时候，其他代码引用时候可以通过key来引用，例如：
// BUCK配置： exported_headers = {'xxx.h': './src/xxx.h', }// 其他代码引用 #import "xxx.h"
依赖资源文件
如果代码中有资源文件，需要通过apple_resource来引用
apple_resource(name = 'SubProject1Resource',files = glob(['*.png']),dirs = [], )
特殊的Compiler flag
在iOS中，有些源代码需要一些特殊的compiler flag，例如非ARC的源码。在src里面可以进行配置:
srcs = glob(['SubProject1/**/**/**/*.m',], excludes = ['**/**/xxx1.m','**/**/xxx2.m'])+[('src/xxx1.m', ['-Wno-shorten-64-to-32']),('src/xxx2.m', ['-fno-objc-arc'])]
引用外部framework
prebuilt_apple_framework(name = 'BuckTest',framework = 'BuckTest.framework',preferred_linkage = 'shared',visibility = ['PUBLIC'], )
引用外部.a 静态库
如下项目有依赖外部的.a库，可以通过以下方法引用
cxx_library(name = 'lib1',srcs = [],exported_headers = {'xxx.h': 'libs/xxx.h',},visibility = ['PUBLIC'], )apple_library(name = 'SubProject1Lib',deps = [':lib1'],...libraries = ['libs/xxx.a',],
当前BUCK的局限性
BUCK本身目前还在快速迭代中，所以很多rule还没有完善、文档不全，社区也够活跃，遇到问题会比较难找到解决方案。
目前iOS项目中碰到的一些限制问题：
- 自定义的script，在XCode的build phase中可以自定义一些shell脚本，但是在BUCK中没有找到对应的方式
- 无法生成.bundle资源包，iOS打包过程中每个子工程都会产出一个.a和.bundle文件，但是BUCK打包不会产出.bundle文件只会有.a，资源文件只能通过apple_resource()来管理作为其他rule的依赖。
- 通过apple_library()生成.a文件似乎目前还没办法指定valid architectures。
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