[cmake] simplify SWIG config (#6648)

Co-authored-by: James Lamb <jaylamb20@gmail.com>

CMakeLists.txt

@@ -59,10 +59,10 @@ if(__INTEGRATE_OPENCL)
   message(STATUS "Building library with integrated OpenCL components")
 endif()
 
-if(__BUILD_FOR_PYTHON OR __BUILD_FOR_R)
-    # the Python and R package don't require the CLI
+if(__BUILD_FOR_PYTHON OR __BUILD_FOR_R OR USE_SWIG)
+    # the SWIG wrapper, the Python and R package don't require the CLI
     set(BUILD_CLI OFF)
-    # installing the R and Python package shouldn't place LightGBM's headers
+    # installing the SWIG wrapper, the R and Python package shouldn't place LightGBM's headers
     # outside of where the package is installed
     set(INSTALL_HEADERS OFF)
 endif()
@@ -104,15 +104,16 @@ if(USE_SWIG)
   include_directories(JNI_INCLUDE_DIRS)
   include_directories($ENV{JAVA_HOME}/include)
   if(WIN32)
-      file(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/com/microsoft/ml/lightgbm/windows/x86_64")
+      set(LGBM_SWIG_DESTINATION_DIR "${CMAKE_CURRENT_BINARY_DIR}/com/microsoft/ml/lightgbm/windows/x86_64")
       include_directories($ENV{JAVA_HOME}/include/win32)
   elseif(APPLE)
-      file(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/com/microsoft/ml/lightgbm/osx/x86_64")
+      set(LGBM_SWIG_DESTINATION_DIR "${CMAKE_CURRENT_BINARY_DIR}/com/microsoft/ml/lightgbm/osx/x86_64")
       include_directories($ENV{JAVA_HOME}/include/darwin)
   else()
-      file(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/com/microsoft/ml/lightgbm/linux/x86_64")
+      set(LGBM_SWIG_DESTINATION_DIR "${CMAKE_CURRENT_BINARY_DIR}/com/microsoft/ml/lightgbm/linux/x86_64")
       include_directories($ENV{JAVA_HOME}/include/linux)
   endif()
+  file(MAKE_DIRECTORY "${LGBM_SWIG_DESTINATION_DIR}")
 endif()
 
 set(EIGEN_DIR "${PROJECT_SOURCE_DIR}/external_libs/eigen")
@@ -542,65 +543,23 @@ if(USE_SWIG)
       OUTPUT_NAME "lib_lightgbm_swig"
   )
   if(WIN32)
+    set(LGBM_SWIG_LIB_DESTINATION_PATH "${LGBM_SWIG_DESTINATION_DIR}/lib_lightgbm_swig.dll")
     if(MINGW OR CYGWIN)
-        add_custom_command(
-            TARGET _lightgbm_swig
-            POST_BUILD
-            COMMAND "${Java_JAVAC_EXECUTABLE}" -d . java/*.java
-            COMMAND
-              "${CMAKE_COMMAND}"
-              -E
-              copy_if_different
-              "${PROJECT_SOURCE_DIR}/lib_lightgbm.dll"
-              com/microsoft/ml/lightgbm/windows/x86_64
-            COMMAND
-              "${CMAKE_COMMAND}"
-              -E
-              copy_if_different
-              "${PROJECT_SOURCE_DIR}/lib_lightgbm_swig.dll"
-              com/microsoft/ml/lightgbm/windows/x86_64
-            COMMAND "${Java_JAR_EXECUTABLE}" -cf lightgbmlib.jar com
-        )
+        set(LGBM_LIB_SOURCE_PATH "${PROJECT_SOURCE_DIR}/lib_lightgbm.dll")
+        set(LGBM_SWIG_LIB_SOURCE_PATH "${PROJECT_SOURCE_DIR}/lib_lightgbm_swig.dll")
     else()
-        add_custom_command(
-            TARGET _lightgbm_swig
-            POST_BUILD
-            COMMAND "${Java_JAVAC_EXECUTABLE}" -d . java/*.java
-            COMMAND
-              "${CMAKE_COMMAND}"
-              -E
-              copy_if_different
-              "${PROJECT_SOURCE_DIR}/Release/lib_lightgbm.dll"
-              com/microsoft/ml/lightgbm/windows/x86_64
-            COMMAND
-              "${CMAKE_COMMAND}"
-              -E
-              copy_if_different
-              "${PROJECT_SOURCE_DIR}/Release/lib_lightgbm_swig.dll"
-              com/microsoft/ml/lightgbm/windows/x86_64
-            COMMAND "${Java_JAR_EXECUTABLE}" -cf lightgbmlib.jar com
-        )
+        set(LGBM_LIB_SOURCE_PATH "${PROJECT_SOURCE_DIR}/Release/lib_lightgbm.dll")
+        set(LGBM_SWIG_LIB_SOURCE_PATH "${PROJECT_SOURCE_DIR}/Release/lib_lightgbm_swig.dll")
     endif()
   elseif(APPLE)
-    add_custom_command(
-        TARGET _lightgbm_swig
-        POST_BUILD
-        COMMAND "${Java_JAVAC_EXECUTABLE}" -d . java/*.java
-        COMMAND
-          "${CMAKE_COMMAND}"
-          -E
-          copy_if_different
-          "${PROJECT_SOURCE_DIR}/lib_lightgbm.dylib"
-          com/microsoft/ml/lightgbm/osx/x86_64
-        COMMAND
-          "${CMAKE_COMMAND}"
-          -E
-          copy_if_different
-          "${PROJECT_SOURCE_DIR}/lib_lightgbm_swig.jnilib"
-          com/microsoft/ml/lightgbm/osx/x86_64/lib_lightgbm_swig.dylib
-        COMMAND "${Java_JAR_EXECUTABLE}" -cf lightgbmlib.jar com
-    )
+    set(LGBM_LIB_SOURCE_PATH "${PROJECT_SOURCE_DIR}/lib_lightgbm.dylib")
+    set(LGBM_SWIG_LIB_SOURCE_PATH "${PROJECT_SOURCE_DIR}/lib_lightgbm_swig.jnilib")
+    set(LGBM_SWIG_LIB_DESTINATION_PATH "${LGBM_SWIG_DESTINATION_DIR}/lib_lightgbm_swig.dylib")
   else()
+    set(LGBM_LIB_SOURCE_PATH "${PROJECT_SOURCE_DIR}/lib_lightgbm.so")
+    set(LGBM_SWIG_LIB_SOURCE_PATH "${PROJECT_SOURCE_DIR}/lib_lightgbm_swig.so")
+    set(LGBM_SWIG_LIB_DESTINATION_PATH "${LGBM_SWIG_DESTINATION_DIR}/lib_lightgbm_swig.so")
+  endif()
   add_custom_command(
       TARGET _lightgbm_swig
       POST_BUILD
@@ -609,17 +568,16 @@ if(USE_SWIG)
         "${CMAKE_COMMAND}"
         -E
         copy_if_different
-          "${PROJECT_SOURCE_DIR}/lib_lightgbm.so"
-          com/microsoft/ml/lightgbm/linux/x86_64
+        "${LGBM_LIB_SOURCE_PATH}"
+        "${LGBM_SWIG_DESTINATION_DIR}"
       COMMAND
         "${CMAKE_COMMAND}"
         -E
         copy_if_different
-          "${PROJECT_SOURCE_DIR}/lib_lightgbm_swig.so"
-          com/microsoft/ml/lightgbm/linux/x86_64
+        "${LGBM_SWIG_LIB_SOURCE_PATH}"
+        "${LGBM_SWIG_LIB_DESTINATION_PATH}"
       COMMAND "${Java_JAR_EXECUTABLE}" -cf lightgbmlib.jar com
     )
-  endif()
 endif()
 
 if(USE_MPI)