lib_proj.cmake: add a PROJ::proj alias and add BUILD_INTERFACE includ…

…e directories, so that proj can be used as a subdirectory of a larger project (fixes #2905)

src/lib_proj.cmake

@@ -372,6 +372,8 @@ add_library(proj
   ${ALL_LIBPROJ_HEADERS}
   ${PROJ_RESOURCES}
 )
+add_library(PROJ::proj ALIAS proj)
+
 target_compile_options(proj
   PRIVATE $<$<COMPILE_LANGUAGE:C>:${PROJ_C_WARN_FLAGS}>
   PRIVATE $<$<COMPILE_LANGUAGE:CXX>:${PROJ_CXX_WARN_FLAGS}>
@@ -402,6 +404,8 @@ if(ENABLE_IPO)
 endif()
 
 target_include_directories(proj INTERFACE
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+  $<BUILD_INTERFACE:${PROJ_SOURCE_DIR}/include>
   $<INSTALL_INTERFACE:${INCLUDEDIR}>)
 
 if(WIN32)

travis/install.sh

@@ -116,6 +116,21 @@ fi
 if [ "$BUILD_NAME" != "linux_gcc8" -a "$BUILD_NAME" != "linux_gcc_32bit" ]; then
 
     # cmake build from generated tarball
+    mkdir proj_as_subproject
+    cd proj_as_subproject
+    mkdir external
+    ln -s $PWD/.. external/PROJ
+
+    echo '#include "proj.h"' > mytest.c
+    echo 'int main() { proj_info(); return 0; }' >> mytest.c
+
+    echo 'cmake_minimum_required(VERSION 3.9)' > CMakeLists.txt
+    echo 'project(mytest)' >> CMakeLists.txt
+    echo 'add_subdirectory(external/PROJ)' >> CMakeLists.txt
+    echo 'add_executable(mytest mytest.c)' >> CMakeLists.txt
+    echo 'target_include_directories(mytest PRIVATE $<TARGET_PROPERTY:PROJ::proj,INTERFACE_INCLUDE_DIRECTORIES>)' >> CMakeLists.txt
+    echo 'target_link_libraries(mytest PRIVATE PROJ::proj)' >> CMakeLists.txt
+
     mkdir build_cmake
     cd build_cmake
     cmake --version
@@ -130,7 +145,7 @@ if [ "$BUILD_NAME" != "linux_gcc8" -a "$BUILD_NAME" != "linux_gcc_32bit" ]; then
     else
         echo "Skipping test_cmake.sh test for $BUILD_NAME"
     fi
-    cd ..
+    cd ../..
 
     if [ $TRAVIS_OS_NAME != "osx" ]; then
         # Check that we can retrieve the resource directory in a relative way after renaming the installation prefix