Support building on Linux.

By default, Linux uses a locally-built version of core that is prepared
in an independent working copy of the realm-core git repository.

Support is also added for using an existing local build of core on both
OS X and Linux . This can be done by running
`cmake -DREALM_CORE_VERSION=/path/to/realm-core`. The generated build
system will invoke `sh build.sh build` within the given directory prior
to building the object store.

.gitignore

@@ -9,5 +9,5 @@ cmake_install.cmake
 rules.ninja
 
 # Build products
-librealm-object-store.dylib
+src/librealm-object-store.*
 tests/tests

CMake/RealmCore.cmake

@@ -1,5 +1,26 @@
 include(ExternalProject)
 
+if(${CMAKE_GENERATOR} STREQUAL "Unix Makefiles")
+    set(MAKE_EQUAL_MAKE "MAKE=$(MAKE)")
+endif()
+
+if (${CMAKE_VERSION} VERSION_GREATER "3.4.0")
+    set(USES_TERMINAL_BUILD USES_TERMINAL_BUILD 1)
+endif()
+
+function(use_realm_core version_or_path_to_source)
+    if("${version_or_path_to_source}" MATCHES "^[0-9]+(\\.[0-9])+")
+        if(APPLE)
+            download_realm_core(${version_or_path_to_source})
+        else()
+            clone_and_build_realm_core("v${version_or_path_to_source}")
+        endif()
+    else()
+        build_existing_realm_core(${version_or_path_to_source})
+    endif()
+    set(REALM_CORE_INCLUDE_DIR ${REALM_CORE_INCLUDE_DIR} PARENT_SCOPE)
+endfunction()
+
 function(download_realm_core core_version)
     set(core_url "https://static.realm.io/downloads/core/realm-core-${core_version}.tar.bz2")
     set(core_tarball_name "realm-core-${core_version}.tar.bz2")
@@ -40,3 +61,72 @@ function(download_realm_core core_version)
 
     set(REALM_CORE_INCLUDE_DIR ${core_directory}/include PARENT_SCOPE)
 endfunction()
+
+function(clone_and_build_realm_core branch)
+    set(core_prefix_directory "${CMAKE_CURRENT_SOURCE_DIR}${CMAKE_FILES_DIRECTORY}/realm-core")
+    ExternalProject_Add(realm-core
+        GIT_REPOSITORY "git@github.com:realm/realm-core.git"
+        GIT_TAG ${branch}
+        PREFIX ${core_prefix_directory}
+        BUILD_IN_SOURCE 1
+        CONFIGURE_COMMAND ""
+        BUILD_COMMAND ${MAKE_EQUAL_MAKE} sh build.sh build
+        INSTALL_COMMAND ""
+        ${USES_TERMINAL_BUILD}
+        )
+
+    ExternalProject_Get_Property(realm-core SOURCE_DIR)
+    set(core_directory ${SOURCE_DIR})
+    set(core_library_debug ${core_directory}/src/realm/librealm-dbg${CMAKE_SHARED_LIBRARY_SUFFIX})
+    set(core_library_release ${core_directory}/src/realm/librealm${CMAKE_SHARED_LIBRARY_SUFFIX})
+    set(core_libraries ${core_library_debug} ${core_library_release})
+
+    ExternalProject_Add_Step(realm-core ensure-libraries
+        COMMAND ${CMAKE_COMMAND} -E touch_nocreate ${core_libraries}
+        OUTPUT ${core_libraries}
+        DEPENDEES build
+        )
+
+    add_library(realm SHARED IMPORTED)
+    add_dependencies(realm realm-core)
+
+    set_property(TARGET realm PROPERTY IMPORTED_LOCATION_DEBUG ${core_library_debug})
+    set_property(TARGET realm PROPERTY IMPORTED_LOCATION_RELEASE ${core_library_release})
+    set_property(TARGET realm PROPERTY IMPORTED_LOCATION ${core_library_release})
+
+    set(REALM_CORE_INCLUDE_DIR ${core_directory}/src PARENT_SCOPE)
+endfunction()
+
+function(build_existing_realm_core core_directory)
+    get_filename_component(core_directory ${core_directory} ABSOLUTE)
+    ExternalProject_Add(realm-core
+        URL ""
+        PREFIX ${CMAKE_CURRENT_SOURCE_DIR}${CMAKE_FILES_DIRECTORY}/realm-core
+        SOURCE_DIR ${core_directory}
+        BUILD_IN_SOURCE 1
+        BUILD_ALWAYS 1
+        CONFIGURE_COMMAND ""
+        BUILD_COMMAND ${MAKE_EQUAL_MAKE} sh build.sh build
+        INSTALL_COMMAND ""
+        ${USES_TERMINAL_BUILD}
+        )
+
+    set(core_library_debug ${core_directory}/src/realm/librealm-dbg${CMAKE_SHARED_LIBRARY_SUFFIX})
+    set(core_library_release ${core_directory}/src/realm/librealm${CMAKE_SHARED_LIBRARY_SUFFIX})
+    set(core_libraries ${core_library_debug} ${core_library_release})
+
+    ExternalProject_Add_Step(realm-core ensure-libraries
+        COMMAND ${CMAKE_COMMAND} -E touch_nocreate ${core_libraries}
+        OUTPUT ${core_libraries}
+        DEPENDEES build
+        )
+
+    add_library(realm SHARED IMPORTED)
+    add_dependencies(realm realm-core)
+
+    set_property(TARGET realm PROPERTY IMPORTED_LOCATION_DEBUG ${core_library_debug})
+    set_property(TARGET realm PROPERTY IMPORTED_LOCATION_RELEASE ${core_library_release})
+    set_property(TARGET realm PROPERTY IMPORTED_LOCATION ${core_library_release})
+
+    set(REALM_CORE_INCLUDE_DIR ${core_directory}/src PARENT_SCOPE)
+endfunction()

CMakeLists.txt

@@ -7,7 +7,8 @@ list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/CMake")
 include(CompilerFlags)
 
 include(RealmCore)
-download_realm_core(0.96.2)
+set(REALM_CORE_VERSION "0.96.2" CACHE STRING "")
+use_realm_core(${REALM_CORE_VERSION})
 
 include_directories(${REALM_CORE_INCLUDE_DIR} src external/pegtl)