[R-package] Introduce R-specific control of lib_lightgbm (#2837)

* [R-package] Introduced define LGB_BUILD_R to control compilation of lib_lightgbm for the R package

* fixed comment

* switched to cmake options

* fixed typo

CMakeLists.txt

@@ -14,6 +14,7 @@ OPTION(USE_HDFS "Enable HDFS support (EXPERIMENTAL)" OFF)
 OPTION(USE_R35 "Set to ON if your R version is not earlier than 3.5" OFF)
 OPTION(USE_TIMETAG "Set to ON to output time costs" OFF)
 OPTION(USE_DEBUG "Set to ON for Debug mode" OFF)
+OPTION(BUILD_FOR_R "Set to ON if building lib_lightgbm for use with the R package" OFF)
 
 if(APPLE)
     OPTION(APPLE_OUTPUT_DYLIB "Output dylib shared library" OFF)
@@ -70,6 +71,10 @@ if(USE_R35)
     ADD_DEFINITIONS(-DR_VER_ABOVE_35)
 endif(USE_R35)
 
+if(BUILD_FOR_R)
+    ADD_DEFINITIONS(-DLGB_R_BUILD)
+endif(BUILD_FOR_R)
+
 if(USE_TIMETAG)
     ADD_DEFINITIONS(-DTIMETAG)
 endif(USE_TIMETAG)

R-package/src/install.libs.R

@@ -43,6 +43,7 @@ if (!use_precompile) {
   if (R_ver >= 3.5) {
     cmake_cmd <- paste0(cmake_cmd, " -DUSE_R35=ON ")
   }
+  cmake_cmd <- paste0(cmake_cmd, " -DBUILD_FOR_R=ON ")
 
   # Check if Windows installation (for gcc vs Visual Studio)
   if (WINDOWS) {

src/io/json11.cpp

@@ -21,7 +21,9 @@
 #include <LightGBM/utils/json11.h>
 
 #include <limits>
-#include <cassert>
+#ifndef LGB_R_BUILD
+  #include <cassert>
+#endif
 #include <cmath>
 #include <cstdio>
 #include <cstdlib>
@@ -624,7 +626,9 @@ struct JsonParser final {
      * the input and return res. If not, flag an error.
      */
     Json expect(const string &expected, Json res) {
+        #ifndef LGB_R_BUILD
           assert(i != 0);
+        #endif
         i--;
         if (str.compare(i, expected.length(), expected) == 0) {
             i += expected.length();