add new CMake option `ABSL_USE_SYSTEM_INCLUDES`

When using Abseil as a dependency with CMake, files that include Abseil headers and have incompatible warning settings can emit compiler warnings. CMake allows you to mark include directories as `SYSTEM` includes, which causes compilers to ignore warnings from those headers. 

This adds the new option `ABSL_USE_SYSTEM_INCLUDES`, which makes Abseil's include directories be marked with `SYSTEM`.
pull/1249/head
Evan Cox 3 years ago
parent 697acabc5b
commit 6f6886156d
  1. 10
      CMake/AbseilHelpers.cmake
  2. 4
      CMakeLists.txt

@ -26,6 +26,12 @@ if(NOT DEFINED ABSL_IDE_FOLDER)
set(ABSL_IDE_FOLDER Abseil)
endif()
if(ABSL_USE_SYSTEM_INCLUDES)
set(ABSL_INTERNAL_INCLUDE_WARNING_GUARD SYSTEM)
else()
set(ABSL_INTERNAL_INCLUDE_WARNING_GUARD "")
endif()
# absl_cc_library()
#
# CMake function to imitate Bazel's cc_library rule.
@ -242,7 +248,7 @@ Cflags: -I\${includedir}${PC_CFLAGS}\n")
# unconditionally.
set_property(TARGET ${_NAME} PROPERTY LINKER_LANGUAGE "CXX")
target_include_directories(${_NAME}
target_include_directories(${_NAME} ${ABSL_INTERNAL_INCLUDE_WARNING_GUARD}
PUBLIC
"$<BUILD_INTERFACE:${ABSL_COMMON_INCLUDE_DIRS}>"
$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
@ -290,7 +296,7 @@ Cflags: -I\${includedir}${PC_CFLAGS}\n")
else()
# Generating header-only library
add_library(${_NAME} INTERFACE)
target_include_directories(${_NAME}
target_include_directories(${_NAME} ${ABSL_INTERNAL_INCLUDE_WARNING_GUARD}
INTERFACE
"$<BUILD_INTERFACE:${ABSL_COMMON_INCLUDE_DIRS}>"
$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>

@ -70,6 +70,10 @@ if((${CMAKE_VERSION} VERSION_GREATER_EQUAL 3.8) AND (NOT ABSL_PROPAGATE_CXX_STD)
message(WARNING "A future Abseil release will default ABSL_PROPAGATE_CXX_STD to ON for CMake 3.8 and up. We recommend enabling this option to ensure your project still builds correctly.")
endif()
option(ABSL_USE_SYSTEM_INCLUDES
"Mark C++ include directories with `SYSTEM` to prevent warnings from headers when using Abseil with incompatible warning flags"
OFF)
list(APPEND CMAKE_MODULE_PATH
${CMAKE_CURRENT_LIST_DIR}/CMake
${CMAKE_CURRENT_LIST_DIR}/absl/copts

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