[R-package] Convert LGBM_GetLastError_R to use R built-in types (#4242)

* [R-package] move some functions over to SEXP objects

* clarify comment

* remove paste0()

* fix registration table

* fix cmake builds

R-package/R/utils.R

@@ -25,38 +25,15 @@ lgb.encode.char <- function(arr, len) {
   return(rawToChar(arr[seq_len(len)]))
 }
 
-# [description] Raise an error. Before raising that error, check for any error message
-#               stored in a buffer on the C++ side.
+# [description] Get the most recent error stored on the C++ side and raise it
+#               as an R error.
 lgb.last_error <- function() {
-  # Perform text error buffering
-  buf_len <- 200L
-  act_len <- 0L
-  err_msg <- raw(buf_len)
   err_msg <- .Call(
     LGBM_GetLastError_R
-    , buf_len
-    , act_len
-    , err_msg
   )
-
-  # Check error buffer
-  if (act_len > buf_len) {
-    buf_len <- act_len
-    err_msg <- raw(buf_len)
-    err_msg <- .Call(
-      LGBM_GetLastError_R
-      , buf_len
-      , act_len
-      , err_msg
-    )
-  }
-
-  stop("api error: ", lgb.encode.char(arr = err_msg, len = act_len))
-
+  stop("api error: ", err_msg)
   return(invisible(NULL))
-
 }
-
 lgb.params2str <- function(params, ...) {
 
   # Check for a list as input

R-package/src/lightgbm_R.cpp

@@ -56,8 +56,12 @@ LGBM_SE EncodeChar(LGBM_SE dest, const char* src, LGBM_SE buf_len, LGBM_SE actua
   return dest;
 }
 
-LGBM_SE LGBM_GetLastError_R(LGBM_SE buf_len, LGBM_SE actual_len, LGBM_SE err_msg) {
-  return EncodeChar(err_msg, LGBM_GetLastError(), buf_len, actual_len, std::strlen(LGBM_GetLastError()) + 1);
+SEXP LGBM_GetLastError_R() {
+  SEXP out;
+  out = PROTECT(Rf_allocVector(STRSXP, 1));
+  SET_STRING_ELT(out, 0, Rf_mkChar(LGBM_GetLastError()));
+  UNPROTECT(1);
+  return out;
 }
 
 SEXP LGBM_DatasetCreateFromFile_R(LGBM_SE filename,
@@ -640,7 +644,7 @@ SEXP LGBM_BoosterDumpModel_R(LGBM_SE handle,
 
 // .Call() calls
 static const R_CallMethodDef CallEntries[] = {
-  {"LGBM_GetLastError_R"              , (DL_FUNC) &LGBM_GetLastError_R              , 3},
+  {"LGBM_GetLastError_R"              , (DL_FUNC) &LGBM_GetLastError_R              , 0},
   {"LGBM_DatasetCreateFromFile_R"     , (DL_FUNC) &LGBM_DatasetCreateFromFile_R     , 4},
   {"LGBM_DatasetCreateFromCSC_R"      , (DL_FUNC) &LGBM_DatasetCreateFromCSC_R      , 9},
   {"LGBM_DatasetCreateFromMat_R"      , (DL_FUNC) &LGBM_DatasetCreateFromMat_R      , 6},

R-package/src/lightgbm_R.h

@@ -15,11 +15,7 @@
 * \return err_msg error information
 * \return error information
 */
-LIGHTGBM_C_EXPORT LGBM_SE LGBM_GetLastError_R(
-    LGBM_SE buf_len,
-    LGBM_SE actual_len,
-    LGBM_SE err_msg
-);
+LIGHTGBM_C_EXPORT SEXP LGBM_GetLastError_R();
 
 // --- start Dataset interface
 

build_r.R

@@ -397,7 +397,7 @@ c_api_contents <- gsub(
   , x = c_api_contents
 )
 c_api_symbols <- gsub(
-  pattern = "\\("
+  pattern = "\\(.*"
   , replacement = ""
   , x = c_api_contents
 )