Bazel Getting Started
本文主要包含两个方面的内容： 1） 演示Bazel的基本使用流程 2) 介绍Bazel使用过程中的一些基本概念
参看:
1. 使用Bazel来构建一个C++工程
执行如下命令从Bazel GitHub仓库克隆出一个sample:
# mkdir bazel-workspace # cd bazel-workspace # git clone https://github.com/bazelbuild/examples
我们来看看本节所需要用到的examples/cpp-tutorial目录：
# tree examples/cpp-tutorial
examples
└── cpp-tutorial
├──stage1
│ ├── main
│ │ ├── BUILD
│ │ └── hello-world.cc
│ └── MODULE.bazel
├──stage2
│ ├── main
│ │ ├── BUILD
│ │ ├── hello-world.cc
│ │ ├── hello-greet.cc
│ │ └── hello-greet.h
│ └── MODULE.bazel
└──stage3
├── main
│ ├── BUILD
│ ├── hello-world.cc
│ ├── hello-greet.cc
│ └── hello-greet.h
├── lib
│ ├── BUILD
│ ├── hello-time.cc
│ └── hello-time.h
└── MODULE.bazel
从上面我们看到cpp-turorial包含3个stage文件夹，本文也分3个stage来进行讲解。在stage1中，我们会从单个package中构建单个target； 在stage2中，我们会从单个package中构建两个target: binary和library； 在stage3中，我们从多个package中构建多个targets。
1.1 预备知识
在我们开始build一个project之前，首先需要创建一个workspace。一个worksapce含有工程源文件和bazel输出的目录，此外目录中通常还会包含如下一些典型的文件：
-
MODULE.bazel文件：用于标识该目录是一个bazel workspace，放置于工程的根目录中， 可以在该文件中指定所需的外部依赖； -
一个或多个
BUILD文件：用于告诉Bazel如何构建工程的不同部分。工程中包含BUILD文件的目录称为package。
1） Understand BUILD file
一个BUILD文件中可以包含许多不同类型的Bazel指令。每个BUILD文件都至少需要设置一个rule，用于告诉bazel如何构建构建你想要的输出。BUILD文件中的每一个rule实例称为target，其指定了构建相应的输出所需要的源文件和依赖项。此外，一个target也可以指向多个其他的targets。
下面我们来看看cpp-tutorial/stage1/main目录下的BUILD文件：
cc_binary(
name = "hello-world",
srcs = ["hello-world.cc"],
)
在我们的例子中，hello-world这个target实例化了bazel的内置cc_binary rule。通过该规则，bazel就知道了需要通过源文件hello-world.cc来构建一个自包含的可执行文件，并且构建时没有其他依赖。
1.2 Stage 1: single target, single package
接下来我们使用bazel来构建stage1这一工程，先来看看该工程的目录结构：
examples
└── cpp-tutorial
└──stage1
├── main
│ ├── BUILD
│ └── hello-world.cc
└── MODULE.bazel
进入到该目录执行如下命令:
# cd cpp-tutorial/stage1 # bazel build //main:hello-world 2024/12/04 14:19:23 Warning: used fallback version "8.0.0rc6" 2024/12/04 14:19:23 Downloading https://releases.bazel.build/8.0.0/rc6/bazel-8.0.0rc6-linux-x86_64... 2024/12/04 14:19:23 Skipping basic authentication for releases.bazel.build because no credentials found in /root/.netrc Downloading: 61 MB out of 61 MB (100%) Extracting Bazel installation... Starting local Bazel server and connecting to it... WARNING: Couldn't auto load rules or symbols, because no dependency on module/repository 'rules_android' found. This will result in a failure if there's a reference to those rules or symbols. INFO: Analyzed target //main:hello-world (68 packages loaded, 468 targets configured). INFO: Found 1 target... Target //main:hello-world up-to-date: bazel-bin/main/hello-world INFO: Elapsed time: 29.465s, Critical Path: 0.27s INFO: 6 processes: 4 internal, 2 linux-sandbox. INFO: Build completed successfully, 6 total actions
命令执行后我们来看看所产生的output:
# tree
.
├── bazel-bin -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/bin
├── bazel-out -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out
├── bazel-stage1 -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main
├── bazel-testlogs -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/testlogs
├── main
│ ├── BUILD
│ └── hello-world.cc
├── MODULE.bazel
├── MODULE.bazel.lock
└── README.md
5 directories, 5 files
# tree bazel-bin
bazel-bin
└── main
├── hello-world
├── hello-world-0.params
├── hello-world.repo_mapping
├── hello-world.runfiles
│ ├── _main
│ │ └── main
│ │ └── hello-world -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/bin/main/hello-world
│ ├── MANIFEST -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/bin/main/hello-world.runfiles_manifest
│ └── _repo_mapping -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/bin/main/hello-world.repo_mapping
├── hello-world.runfiles_manifest
└── _objs
└── hello-world
├── hello-world.pic.d
└── hello-world.pic.o
6 directories, 9 files
# tree bazel-out
bazel-out
├── k8-fastbuild
│ ├── bin
│ │ └── main
│ │ ├── hello-world
│ │ ├── hello-world-0.params
│ │ ├── hello-world.repo_mapping
│ │ ├── hello-world.runfiles
│ │ │ ├── _main
│ │ │ │ └── main
│ │ │ │ └── hello-world -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/bin/main/hello-world
│ │ │ ├── MANIFEST -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/bin/main/hello-world.runfiles_manifest
│ │ │ └── _repo_mapping -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/bin/main/hello-world.repo_mapping
│ │ ├── hello-world.runfiles_manifest
│ │ └── _objs
│ │ └── hello-world
│ │ ├── hello-world.pic.d
│ │ └── hello-world.pic.o
│ └── testlogs
├── stable-status.txt
├── _tmp
│ └── actions
│ ├── stderr-5
│ ├── stderr-7
│ ├── stdout-5
│ └── stdout-7
└── volatile-status.txt
11 directories, 15 files
# tree bazel-stage1
bazel-stage1
├── bazel-out
│ ├── k8-fastbuild
│ │ ├── bin
│ │ │ └── main
│ │ │ ├── hello-world
│ │ │ ├── hello-world-0.params
│ │ │ ├── hello-world.repo_mapping
│ │ │ ├── hello-world.runfiles
│ │ │ │ ├── _main
│ │ │ │ │ └── main
│ │ │ │ │ └── hello-world -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/bin/main/hello-world
│ │ │ │ ├── MANIFEST -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/bin/main/hello-world.runfiles_manifest
│ │ │ │ └── _repo_mapping -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/execroot/_main/bazel-out/k8-fastbuild/bin/main/hello-world.repo_mapping
│ │ │ ├── hello-world.runfiles_manifest
│ │ │ └── _objs
│ │ │ └── hello-world
│ │ │ ├── hello-world.pic.d
│ │ │ └── hello-world.pic.o
│ │ └── testlogs
│ ├── stable-status.txt
│ ├── _tmp
│ │ └── actions
│ │ ├── stderr-5
│ │ ├── stderr-7
│ │ ├── stdout-5
│ │ └── stdout-7
│ └── volatile-status.txt
├── external
│ ├── bazel_tools -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/external/bazel_tools
│ ├── bazel_tools+xcode_configure_extension+local_config_xcode -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/external/bazel_tools+xcode_configure_extension+local_config_xcode
│ ├── platforms -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/external/platforms
│ ├── rules_cc+ -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/external/rules_cc+
│ └── rules_cc++cc_configure_extension+local_config_cc -> /root/.cache/bazel/_bazel_root/63b5237301a1c80ee5b3af8a4d0a90e9/external/rules_cc++cc_configure_extension+local_config_cc
├── main -> /workspace/cpp_proj/bazel-workspace/examples/cpp-tutorial/stage1/main
├── MODULE.bazel -> /workspace/cpp_proj/bazel-workspace/examples/cpp-tutorial/stage1/MODULE.bazel
├── MODULE.bazel.lock -> /workspace/cpp_proj/bazel-workspace/examples/cpp-tutorial/stage1/MODULE.bazel.lock
└── README.md -> /workspace/cpp_proj/bazel-workspace/examples/cpp-tutorial/stage1/README.md
19 directories, 18 files
# tree bazel-testlogs
bazel-testlogs
0 directories, 0 files
通过前面的编译日志，我们了解到最终的编译输出放在bazel-bin目录。执行如下命令看看编译出来的可执行程序是否正常运行:
# ./bazel-bin/main/hello-world Hello world Wed Dec 4 14:33:03 2024
