when a column has not classes but has the object bit set, pretend it …

NEWS.md

@@ -69,6 +69,8 @@
 
 * Added an `.onDetach()` hook that allows for plyr to be loaded and attached without the warning message that says functions in dplyr will be masked, since dplyr is no longer attached (#3359, @jwnorman).
 
+* `bind_rows()` works around corrupt columns that have the object bit set while having no class attribute (#3349). 
+
 * `arrange()` fails gracefully on `data.frame` columns (#3153)
 
 * `slice()` no longer enforce tibble classes when input is a simple `data.frame` (#3297). 

inst/include/dplyr/Collecter.h

@@ -10,10 +10,10 @@
 namespace dplyr {
 
 static inline bool inherits_from(SEXP x, const std::set<std::string>& classes) {
-  std::vector<std::string> x_classes, inherited_classes;
-  if (!OBJECT(x)) {
-    return false;
+  if (Rf_isNull(Rf_getAttrib(x, R_ClassSymbol))) {
+    return true ;
   }
+  std::vector<std::string> x_classes, inherited_classes;
   x_classes = Rcpp::as< std::vector<std::string> >(Rf_getAttrib(x, R_ClassSymbol));
   std::sort(x_classes.begin(), x_classes.end());
   std::set_intersection(x_classes.begin(), x_classes.end(),
@@ -44,9 +44,8 @@ static bool is_class_known(SEXP x) {
 static inline void warn_loss_attr(SEXP x) {
   /* Attributes are lost with unknown classes */
   if (!is_class_known(x)) {
-    SEXP classes = Rf_getAttrib(x, R_ClassSymbol);
     Rf_warning("Vectorizing '%s' elements may not preserve their attributes",
-               CHAR(STRING_ELT(classes, 0)));
+               CHAR(STRING_ELT(Rf_getAttrib(x, R_ClassSymbol), 0)));
   }
 }
 

tests/testthat/test-binds.R

@@ -571,6 +571,13 @@ test_that("bind_rows() accepts lists of dataframe-like lists as first argument",
   expect_identical(bind_rows(list(list(a = 1, b = 2))), tibble(a = 1, b = 2))
 })
 
+test_that("columns that are OBJECT but have NULL class are handled gracefully (#3349)", {
+  mod <- lm(y~ ., data = freeny)
+  data <- model.frame(mod)
+  data_list <- list(data, data)
+  res <- bind_rows(data_list)
+  expect_equal(names(res), names(data))
+})
 
 # Vectors ------------------------------------------------------------