[Rcpp-devel] Missing PROTECT()s in forward_exception_to_r()?

[North, Ben]

Hi,

I've been using Rcpp for a while now, and finding it very useful ---
thanks!

Recently, though, I came across strange behaviour when running under
gctorture(TRUE) and C++ exceptions were being forwarded to R.  The error
message string at the R level was some essentially random pathname, and
the string in the C++ exception was nowhere to be seen.  The classname
at the R level was the logical TRUE value.

The patch below fixed the problem for me.  I would not claim to fully
know what I'm doing, so perhaps somebody who does could review and then
make the proper fix :-)

Thanks,

Ben.

--- src/exceptions.cpp   2012-10-01 01:29:53.000000000 +0100
+++ ../Rcpp/src/exceptions.cpp     2012-10-08 11:14:39.435644100 +0100
@@ -161,14 +161,23 @@
               exception_class = name ; /* just using the mangled name */
          }
     }
-    SEXP cppExceptSym = Rf_install("cpp_exception"); // cannot cause a gc() once in symbol table
-    Rf_eval(
-        Rf_lang3(
-         cppExceptSym,
-              Rf_mkString(exception_what.c_str()),
-              Rf_mkString(exception_class.c_str())
-         ), R_FindNamespace(Rf_mkString("Rcpp"))
-    ) ;
+
+    SEXP cppExceptSym;
+    SEXP str_what, str_class, str_ns, ns, expr;
+
+    PROTECT(cppExceptSym = Rf_install("cpp_exception"));
+    PROTECT(str_what = Rf_mkString(exception_what.c_str()));
+    PROTECT(str_class = Rf_mkString(exception_class.c_str()));
+    PROTECT(str_ns = Rf_mkString("Rcpp"));
+
+    PROTECT(ns = R_FindNamespace(str_ns));
+    PROTECT(expr = Rf_lang3(cppExceptSym, str_what, str_class));
+
+    Rf_eval(expr, ns); /* Should not return. */
+
+    // Do this in case somehow someone replaces the definition of
+    // "cpp_exception" such that it does return:
+    UNPROTECT(6);
 }
 #else

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