When found with pkg-config the INTERFACE_INCLUDE_DIRECTORIES property of UUID::UUID is not the one expected by ignition projects

[traversaro]

The uuid.pc file contained in Debian packages is:

prefix=/usr
exec_prefix=/usr
libdir=/usr/lib/x86_64-linux-gnu
includedir=/usr/include

Name: uuid
Description: Universally unique id library
Version: 2.31.1
Requires:
Cflags: -I${includedir}/uuid
Libs: -L${libdir} -luuid

As you can see from the line Cflags: -I${includedir}/uuid, the include directory that is intended to be passed to the compiler is /usr/include/uuid, and given that the header path is /usr/include/uuid/uuid.h, that means that the headers are meant to be consumed as:

#include <uuid.h>

Unfortunately, Ignition libraries such as ignition-transport ( https://github.com/ignitionrobotics/ign-transport/blob/3e84d43aba2c4aeeceda03b3f7ac1647258f6e16/include/ignition/transport/Uuid.hh#L32 ), ignition-common ( https://github.com/ignitionrobotics/ign-common/blob/1c75659001becdb4e8f8f444aaabe540cc32e287/include/ignition/common/Uuid.hh#L31 ) and Gazebo ( https://github.com/osrf/gazebo/blob/6fd426b3949c4ca73fa126cde68f5cc4a59522eb/plugins/rest_web/RestWebPlugin.cc#L27 ) consume the headers of the uuid library as:

#include <uuid/uuid.h>

This is working only when uuid is installed in the system prefix /usr, and so /usr/include is part of the default compiler header search path, but it fails if uuid is not installed in the /usr or /usr/local prefix.

TL;DR: On Linux and macOS ignition projects that link UUID::UUID fail to compile if UUID is not installed in the /usr or /usr/local prefixes.

[traversaro]

To ensure both compatibilty with projects that expect the pkg-config-style include #include <uuid.h> and the existing ignition projects that use #include <uuid/uuid.h>, the safer option is to put both <uuid_install_prefix>/include and <uuid_install_prefix>/include/uuid in INTERFACE_INCLUDE_DIRECTORIES.

[traversaro]

Fixed by #104 .