https://github.com/rime/librime/issues/431

--- /CMakeLists.txt
+++ /CMakeLists.txt
@@ -11,6 +11,14 @@
 
 include(GNUInstallDirs)
 
+if(NOT DEFINED BIN_INSTALL_DIR)
+    set(BIN_INSTALL_DIR ${CMAKE_INSTALL_BINDIR})
+endif()
+
+if(NOT DEFINED LIB_INSTALL_DIR)
+    set(LIB_INSTALL_DIR ${CMAKE_INSTALL_LIBDIR})
+endif()
+
 option(BUILD_SHARED_LIBS "Build Rime as shared library" ON)
 option(BUILD_MERGED_PLUGINS "Merge plugins into one Rime library" ON)
 option(BUILD_STATIC "Build with dependencies as static libraries" OFF)
@@ -22,8 +30,11 @@
 option(BOOST_USE_CXX11 "Boost has been built with C++11 support" OFF)
 option(BOOST_USE_SIGNALS2 "Boost use signals2 instead of signals" ON)
 option(ENABLE_ASAN "Enable Address Sanitizer (Unix Only)" OFF)
+option(INSTALL_PRIVATE_HEADERS "Install private headers (usually needed for externally built Rime plugins)" OFF)
+option(ENABLE_EXTERNAL_PLUGINS "Enable loading of externally built Rime plugins (from directory set by RIME_PLUGINS_DIR variable)" OFF)
 
-set(rime_data_dir "/share/rime-data" CACHE STRING "Target directory for Rime data")
+set(RIME_DATA_DIR "share/rime-data" CACHE STRING "Target directory for Rime data")
+set(RIME_PLUGINS_DIR "${LIB_INSTALL_DIR}/rime-plugins" CACHE STRING "Target directory for externally built Rime plugins")
 
 if(WIN32)
   set(ext ".exe")
@@ -61,7 +72,7 @@
 set(BOOST_COMPONENTS filesystem regex system)
 
 if(BOOST_USE_SIGNALS2)
-  add_definitions("-DBOOST_SIGNALS2")
+  set(RIME_BOOST_SIGNALS2 1)
 else()
   set(BOOST_COMPONENTS ${BOOST_COMPONENTS} signals)
 endif()
@@ -89,7 +100,7 @@
     add_definitions(-DGOOGLE_GLOG_DLL_DECL=)
   endif()
 
-  add_definitions(-DRIME_ENABLE_LOGGING)
+  set(RIME_ENABLE_LOGGING 1)
 
 endif()
 
@@ -134,6 +145,11 @@
   message(WARNING "X11/keysym.h not found.")
 endif()
 
+configure_file(
+  "${PROJECT_SOURCE_DIR}/src/rime/build_config.h.in"
+  "${PROJECT_BINARY_DIR}/src/rime/build_config.h")
+
+include_directories(${PROJECT_BINARY_DIR}/src)
 include_directories(${PROJECT_SOURCE_DIR}/src)
 include_directories(${PROJECT_SOURCE_DIR}/thirdparty/include)
 link_directories(${PROJECT_SOURCE_DIR}/thirdparty/lib)
@@ -154,14 +170,6 @@
   set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
 endif()
 
-if(NOT DEFINED LIB_INSTALL_DIR)
-    set(LIB_INSTALL_DIR ${CMAKE_INSTALL_LIBDIR})
-endif()
-
-if(NOT DEFINED BIN_INSTALL_DIR)
-    set(BIN_INSTALL_DIR ${CMAKE_INSTALL_BINDIR})
-endif()
-
 # uninstall target
 configure_file(
   "${CMAKE_CURRENT_SOURCE_DIR}/cmake/cmake_uninstall.cmake.in"
@@ -175,7 +183,8 @@
   set(exec_prefix "${CMAKE_INSTALL_PREFIX}")
   set(bindir "${exec_prefix}/${BIN_INSTALL_DIR}")
   set(libdir "${exec_prefix}/${LIB_INSTALL_DIR}")
-  set(pkgdatadir "${prefix}${rime_data_dir}")
+  set(pkgdatadir "${prefix}/${RIME_DATA_DIR}")
+  set(pluginsdir "${exec_prefix}/${RIME_PLUGINS_DIR}")
   set(includedir "${prefix}/${CMAKE_INSTALL_INCLUDEDIR}")
   configure_file(
       ${PROJECT_SOURCE_DIR}/rime.pc.in
@@ -189,11 +198,19 @@
 
 file(GLOB rime_public_header_files ${PROJECT_SOURCE_DIR}/src/*.h)
 install(FILES ${rime_public_header_files} DESTINATION include)
+if(INSTALL_PRIVATE_HEADERS)
+  file(GLOB rime_private_header_files ${PROJECT_SOURCE_DIR}/src/rime/*.h ${PROJECT_BINARY_DIR}/src/rime/*.h)
+  install(FILES ${rime_private_header_files} DESTINATION include/rime)
+  foreach(rime_private_header_files_dir algo config dict gear lever)
+    file(GLOB rime_private_header_files ${PROJECT_SOURCE_DIR}/src/rime/${rime_private_header_files_dir}/*.h)
+    install(FILES ${rime_private_header_files} DESTINATION include/rime/${rime_private_header_files_dir})
+  endforeach()
+endif()
 
 if(BUILD_DATA)
   file(GLOB rime_preset_data_files ${PROJECT_SOURCE_DIR}/data/preset/*.yaml)
   install(FILES ${rime_preset_data_files}
-    DESTINATION ${CMAKE_INSTALL_PREFIX}${rime_data_dir})
+    DESTINATION ${CMAKE_INSTALL_PREFIX}/${RIME_DATA_DIR})
 endif()
 
 if(BUILD_SHARED_LIBS)
@@ -223,6 +240,11 @@
   set(rime_plugins_library rime-plugins)
 endif()
 
+add_definitions("-DRIME_PLUGINS_DIR=\"${CMAKE_INSTALL_PREFIX}/${RIME_PLUGINS_DIR}\"")
+if(ENABLE_EXTERNAL_PLUGINS)
+  add_definitions(-DRIME_ENABLE_EXTERNAL_PLUGINS)
+endif()
+
 add_subdirectory(src)
 
 if(BUILD_SHARED_LIBS)
--- /rime.pc.in
+++ /rime.pc.in
@@ -2,6 +2,8 @@
 exec_prefix=@exec_prefix@
 libdir=@libdir@
 includedir=@includedir@
+pkgdatadir=@pkgdatadir@
+pluginsdir=@pluginsdir@
 
 Name: Rime
 Description: Rime Input Method Engine
--- /src/CMakeLists.txt
+++ /src/CMakeLists.txt
@@ -36,6 +36,9 @@
 if(Gflags_FOUND)
   set(rime_optional_deps ${rime_optional_deps} ${Gflags_LIBRARY})
 endif()
+if(ENABLE_EXTERNAL_PLUGINS)
+  set(rime_optional_deps ${rime_optional_deps} dl)
+endif()
 
 set(rime_core_deps
     ${Boost_LIBRARIES}
--- /src/rime/build_config.h.in
+++ /src/rime/build_config.h.in
@@ -0,0 +1,11 @@
+//
+// Copyright RIME Developers
+// Distributed under the BSD License
+//
+#ifndef RIME_BUILD_CONFIG_H_
+#define RIME_BUILD_CONFIG_H_
+
+#cmakedefine RIME_BOOST_SIGNALS2
+#cmakedefine RIME_ENABLE_LOGGING
+
+#endif  // RIME_BUILD_CONFIG_H_
--- /src/rime/common.h
+++ /src/rime/common.h
@@ -7,6 +7,8 @@
 #ifndef RIME_COMMON_H_
 #define RIME_COMMON_H_
 
+#include <rime/build_config.h>
+
 #include <functional>
 #include <list>
 #include <map>
@@ -20,7 +22,7 @@
 #include <vector>
 #include <boost/optional.hpp>
 #define BOOST_BIND_NO_PLACEHOLDERS
-#ifdef BOOST_SIGNALS2
+#ifdef RIME_BOOST_SIGNALS2
 #include <boost/signals2/connection.hpp>
 #include <boost/signals2/signal.hpp>
 #else
@@ -79,7 +81,7 @@
   return std::make_shared<T>(std::forward<Args>(args)...);
 }
 
-#ifdef BOOST_SIGNALS2
+#ifdef RIME_BOOST_SIGNALS2
 using boost::signals2::connection;
 using boost::signals2::signal;
 #else
--- /src/rime/lever/deployment_tasks.cc
+++ /src/rime/lever/deployment_tasks.cc
@@ -4,6 +4,9 @@
 //
 // 2011-12-10 GONG Chen <chen.sst@gmail.com>
 //
+
+#include <rime/build_config.h>
+
 #include <algorithm>
 #include <boost/algorithm/string.hpp>
 #include <boost/filesystem.hpp>
--- /src/rime/setup.cc
+++ /src/rime/setup.cc
@@ -5,6 +5,13 @@
 // 2011-10-02 GONG Chen <chen.sst@gmail.com>
 //
 
+#include <rime/build_config.h>
+
+#ifdef RIME_ENABLE_EXTERNAL_PLUGINS
+#include <dlfcn.h>
+#include <glob.h>
+#endif // RIME_ENABLE_EXTERNAL_PLUGINS
+
 #ifdef RIME_ENABLE_LOGGING
 #include <glog/logging.h>
 #endif  // RIME_ENABLE_LOGGING
@@ -36,6 +43,32 @@
       mm.LoadModule(module);
     }
   }
+
+#ifdef RIME_ENABLE_EXTERNAL_PLUGINS
+  fs::path plugins_dir = fs::path(RIME_PLUGINS_DIR);
+  fs::path plugins_files = plugins_dir / "*.so";
+  glob_t glob_buffer;
+  if (glob(plugins_files.string().c_str(), 0, NULL, &glob_buffer) == 0) {
+    for (size_t i = 0; i < glob_buffer.gl_pathc; i++) {
+      fs::path plugin_file(glob_buffer.gl_pathv[i]);
+      fs::path plugin_name = plugin_file.stem();
+      fs::file_status plugin_file_status = fs::status(plugin_file);
+      if (fs::is_regular_file(plugin_file) &&
+          plugin_file_status.permissions() & (fs::owner_exe | fs::group_exe | fs::others_exe)) {
+        void* handle = dlopen(plugin_file.string().c_str(), RTLD_LAZY);
+        if (handle) {
+          if (RimeModule* module = mm.Find(plugin_name.string())) {
+            mm.LoadModule(module);
+          }
+        }
+        else {
+          LOG(ERROR) << "dlopen error: " << dlerror();
+        }
+      }
+    }
+    globfree(&glob_buffer);
+  }
+#endif
 }
 
 // assume member is a non-null pointer in struct *p.