test for and report unavailable package in linkingto (closes #1026)

Author: eddelbuettel

ChangeLog

@@ -1,3 +1,7 @@
+2019-11-20  Dirk Eddelbuettel  <[email protected]>
+
+	* R/Attributes.R: Test for and report unavailable 'LinkingTo' package
+
 2019-11-19  Dirk Eddelbuettel  <[email protected]>
 
 	* DESCRIPTION (Version, Date): Roll minor version

R/Attributes.R

@@ -962,6 +962,11 @@ sourceCppFunction <- function(func, isVoid, dll, symbol) {
         # otherwise check for standard Rcpp::interfaces generated include
         else if (!pluginsOnly) {
             pkgPath <- find.package(package, NULL, quiet=TRUE)
+            if (length(pkgPath) == 0) {
+                stop(paste("Package '", package, "' referenced from ",
+                           "LinkingTo directive is not available.", sep=""),
+                     call. = FALSE)
+            }
             pkgHeader <- paste(package, ".h", sep="")
             pkgHeaderPath <- file.path(pkgPath, "include",  pkgHeader)
             if (file.exists(pkgHeaderPath)) {