Abseil 빌드와 의존성 — Bazel vs CMake

1
# WORKSPACE
2
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
3

4
http_archive(
5
    name = "com_google_absl",
6
    sha256 = "f50e5ac311a81382da7fa75b97310e4b9006474f9560ac46f54a9967f07d4ae3",
7
    strip_prefix = "abseil-cpp-20240722.0",
8
    urls = ["https://github.com/abseil/abseil-cpp/releases/download/20240722.0/abseil-cpp-20240722.0.tar.gz"],
9
)

1
# MODULE.bazel — bzlmod
2
bazel_dep(name = "abseil-cpp", version = "20240722.0")

1
cc_library(
2
    name = "my_lib",
3
    srcs = ["my_lib.cc"],
4
    hdrs = ["my_lib.h"],
5
    deps = [
6
        "@com_google_absl//absl/strings",
7
        "@com_google_absl//absl/status",
8
        "@com_google_absl//absl/container:flat_hash_map",
9
    ],
10
)

1
cmake_minimum_required(VERSION 3.16)
2
project(my_project CXX)
3
set(CMAKE_CXX_STANDARD 17)
4
set(CMAKE_CXX_STANDARD_REQUIRED ON)
5

6
include(FetchContent)
7
FetchContent_Declare(
8
    abseil-cpp
9
    GIT_REPOSITORY https://github.com/abseil/abseil-cpp.git
10
    GIT_TAG 20240722.0
11
)
12
set(ABSL_PROPAGATE_CXX_STD ON)
13
set(BUILD_TESTING OFF)
14
FetchContent_MakeAvailable(abseil-cpp)
15

16
add_executable(my_app main.cc)
17
target_link_libraries(my_app PRIVATE
18
    absl::strings
19
    absl::status
20
    absl::flat_hash_map
21
)

1
# Abseil source를 third_party/abseil-cpp에 git submodule로 둔 경우
2
set(ABSL_PROPAGATE_CXX_STD ON)
3
add_subdirectory(third_party/abseil-cpp)
4

5
target_link_libraries(my_app PRIVATE absl::strings)

1
find_package(absl REQUIRED)
2
target_link_libraries(my_app PRIVATE absl::strings)

1
find_package(absl CONFIG REQUIRED)
2
target_link_libraries(my_app PRIVATE absl::strings absl::status)

1
{
2
    "name": "my-project",
3
    "version": "1.0.0",
4
    "dependencies": [
5
        "abseil"
6
    ],
7
    "builtin-baseline": "..."
8
}

1
target_link_libraries(my_app PRIVATE absl::status)
2
# absl::strings, absl::synchronization 등이 자동으로 따라온다

1
set(ABSL_PROPAGATE_CXX_STD ON)         # 사용자 C++ 표준을 따름
2
set(ABSL_USE_EXTERNAL_GOOGLETEST OFF)
3
set(ABSL_FIND_GOOGLETEST OFF)
4
set(BUILD_TESTING OFF)
5
set(ABSL_ENABLE_INSTALL OFF)           # 시스템 설치 안 함

1
# 회피 — find_package(absl) 단독
2
find_package(absl REQUIRED)
3
# 시스템에 깔린 Abseil을 가정. 빌드 환경마다 결과가 다를 수 있다.
4

5
# Good — FetchContent로 명시적 버전 고정
6
FetchContent_Declare(abseil-cpp GIT_TAG 20240722.0)

1
# 회피 — Bazel WORKSPACE에 git_repository(branch="master")
2
git_repository(name = "com_google_absl", remote = "...", branch = "master")
3
# 빌드마다 다른 commit을 가져올 수 있음.
4

5
# Good — http_archive에 sha256 고정
6
http_archive(name = "com_google_absl", sha256 = "f50e...", urls = [...])

1
# 회피 — Abseil을 PUBLIC으로 expose
2
target_link_libraries(my_lib PUBLIC absl::strings)
3
# 사용자 코드가 자동으로 Abseil header를 보게 됨.
4
# 사용자가 다른 버전의 Abseil을 쓰고 있다면 충돌.
5

6
# Good — 가능하면 PRIVATE
7
target_link_libraries(my_lib PRIVATE absl::strings)
8
# 인터페이스에 string_view 같은 type이 노출되면 어쩔 수 없이 PUBLIC.

1
# 회피 — system Abseil + bundled Abseil 혼용
2
find_package(absl REQUIRED)
3
add_subdirectory(third_party/abseil-cpp)  # 충돌