Bazel 概念与对象

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CPP use cases

Adding include paths

https://bazel.build/tutorials/cpp-use-cases#add-include-paths

Sometimes you cannot (or do not want to) root include paths at the workspace root. Existing libraries might already have an include directory that doesn’t match its path in your workspace. For example, suppose you have the following directory structure:

└── my-project
    ├── legacy
    │   └── some_lib
    │       ├── BUILD
    │       ├── include
    │       │   └── some_lib.h
    │       └── some_lib.cc
    └── WORKSPACE

Bazel will expect some_lib.h to be included as legacy/some_lib/include/some_lib.h, but suppose some_lib.cc includes "some_lib.h". To make that include path valid, legacy/some_lib/BUILD will need to specify that the some_lib/include directory is an include directory:

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cc_library(
    name = "some_lib",
    srcs = ["some_lib.cc"],
    hdrs = ["include/some_lib.h"],
    copts = ["-Ilegacy/some_lib/include"],
)

This is especially useful for external dependencies, as their header files must otherwise be included with a / prefix.

Include external libraries

https://bazel.build/tutorials/cpp-use-cases#include-external-libraries

Suppose you are using Google Test {: .external}. You can use one of the repository functions in the WORKSPACE file to download Google Test and make it available in your repository:

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load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

http_archive(
    name = "gtest",
    url = "https://github.com/google/googletest/archive/release-1.10.0.zip",
    sha256 = "94c634d499558a76fa649edb13721dce6e98fb1e7018dfaeba3cd7a083945e91",
    build_file = "@//:gtest.BUILD",
)

Note: If the destination already contains a BUILD file, you can leave out the build_file attribute.

Then create gtest.BUILD, a BUILD file used to compile Google Test.

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cc_library(
    name = "main",
    srcs = glob(
        ["googletest-release-1.10.0/googletest/src/*.cc"],
        exclude = ["googletest-release-1.10.0/googletest/src/gtest-all.cc"]
    ),
    hdrs = glob([
        "googletest-release-1.10.0/googletest/include/**/*.h",
        "googletest-release-1.10.0/googletest/src/*.h"
    ]),
    copts = [
        "-Iexternal/gtest/googletest-release-1.10.0/googletest/include",
        "-Iexternal/gtest/googletest-release-1.10.0/googletest"
    ],
    linkopts = ["-pthread"],
    visibility = ["//visibility:public"],
)

Writing and running C++ tests

https://bazel.build/tutorials/cpp-use-cases#run-c-tests

For example, you could create a test ./test/hello-test.cc, such as:

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#include "gtest/gtest.h"
#include "main/hello-greet.h"

TEST(HelloTest, GetGreet) {
  EXPECT_EQ(get_greet("Bazel"), "Hello Bazel");
}

Then create ./test/BUILD file for your tests:

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cc_test(
    name = "hello-test",
    srcs = ["hello-test.cc"],
    copts = [
      "-Iexternal/gtest/googletest/include",
      "-Iexternal/gtest/googletest",
    ],
    deps = [
        "@gtest//:main",
        "//main:hello-greet",
    ],
)

To make hello-greet visible to hello-test, you must add "//test:__pkg__", to the visibility attribute in ./main/BUILD.

Now you can use bazel test to run the test.

bazel test test:hello-test

This produces the following output:

INFO: Found 1 test target...
Target //test:hello-test up-to-date:
  bazel-bin/test/hello-test
INFO: Elapsed time: 4.497s, Critical Path: 2.53s
//test:hello-test PASSED in 0.3s

Executed 1 out of 1 tests: 1 test passes.

External Dependency

Directory layout

https://bazel.build/external/overview#directory-layout

After being fetched, the repo can be found in the subdirectory external in the output base, under its canonical name.

You can run the following command to see the contents of the repo with the canonical name canonical_name:

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ls $(bazel info output_base)/external/ canonical_name 

e.g:

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/workspaces/envoy$ bazel info output_base
/build/.cache/bazel/_bazel_vscode/2d35de14639eaad1ac7060a4dd7e3351

Inspect

Query

https://bazel.build/query/guide

https://bazel.build/query/language

dependency graph

https://bazel.build/tutorials/cpp-dependency

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bazel query --notool_deps --noimplicit_deps "deps(//main:hello-world)" \
  --output graph

Envoy repo as example:

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bazel query "deps(//source/exe:envoy)"

bazel query --notool_deps "deps(//source/exe:envoy)" --output graph | dot -Tsvg > /tmp/deps.svg

What packages exist beneath(下面) //source/

$ bazel query '//source/...' --output package | head
Loading: 0 packages loaded
source/common/access_log
source/common/api
source/common/buffer
source/common/common
source/common/config
source/common/conn_pool
source/common/crypto
source/common/event
source/common/filesystem
source/common/filter

What rules are defined in the //source/exe package?

$ bazel query 'kind(rule, //source/exe:*)' --output label_kind | head
Loading: 0 packages loaded
alias rule //source/exe:envoy
cc_binary rule //source/exe:envoy-static
cc_library rule //source/exe:envoy_common_lib
cc_library rule //source/exe:envoy_common_lib_with_external_headers
cc_library rule //source/exe:envoy_common_with_core_extensions_lib
cc_library rule //source/exe:envoy_common_with_core_extensions_lib_with_external_headers
cc_library rule //source/exe:envoy_main_common_lib
cc_library rule //source/exe:envoy_main_common_lib_with_external_headers
cc_library rule //source/exe:envoy_main_common_with_core_extensions_lib
cc_library rule //source/exe:envoy_main_common_with_core_extensions_lib_with_external_headers

What files are generated by rules in the foo package?

$ bazel query 'kind("generated file", //source/exe:*)'
//source/exe:envoy-static.dwp
//source/exe:envoy-static.stripped
Loading: 0 packages loaded