@Mizux, this problem is not exhibited in Cartographer master. Cartographer master uses ExternalProject_add to build Abseil. standalone_absl is a single imported target. Imported targets' include directories are marked as SYSTEM by default.

The problem is exhibited in my PR cartographer-project/cartographer#1387, where I fetch abseil during configuring, and build it later using add_subdirectory. If we were fixing this on Cartographer's side, we would have to move INTERFACE_SYSTEM_INCLUDE_DIRECTORIES to INTERFACE_INCLUDE_DIRECTORIES for all Abseil targets (and not just a single standalone_abseil target), and there is a whole bunch of them. I am not aware of how you would even enumerate them in CMake in a portable way - there is BUILDSYSTEM_TARGETS, but that exists only in CMake 3.7+.

Originally posted by @ojura in abseil/abseil-cpp#157 (comment)

The existing setup with subdirectories lacks the simplicity users want from a fire and forget start project.

https://github.com/fowles/abseil-hello

Switches to a structure where each branch contains only the information needed for that build system. Major changes:

• cmake now includes googletest
• cmake and bazel build the same code and tests
• neither includes extra subdirectories
• all the README's have been reworked

Because this requires adding several branches, the ordinary "pull request" workflow doesn't work so I am just pointing to a finished repo for you to pull from.