Error message showing column name when trying to write list column

R/write.R

@@ -210,7 +210,10 @@ output_column <- function(x, name) {
 
 #' @export
 output_column.default <- function(x, name) {
-  if (!is.object(x)) return(x)
+  if (!is.object(x) || "AsIs" %in% class(x)) {
+    return(x)
+  }
+
   as.character(x)
 }
 

src/write_delim.cpp

@@ -88,6 +88,21 @@ void stream_delim(
     output << '"';
 }
 
+void validate_col_type(SEXP x, std::string name) {
+  switch (TYPEOF(x)) {
+  case LGLSXP:
+  case INTSXP:
+  case REALSXP:
+  case STRSXP:
+    break;
+  default:
+    cpp11::stop(
+        "Don't know how to handle vector of type %s in column '%s'.",
+        Rf_type2char(TYPEOF(x)),
+        name.c_str());
+  }
+}
+
 template <class Stream>
 void stream_delim(
     Stream& output,
@@ -106,6 +121,12 @@ void stream_delim(
     output << "\xEF\xBB\xBF";
   }
 
+  cpp11::strings names(df.attr("names"));
+  // Validate column types
+  for (int j = 0; j < p; ++j) {
+    validate_col_type(df.at(j), names[j]);
+  }
+
   if (col_names) {
     cpp11::strings names(df.attr("names"));
     for (int j = 0; j < p; ++j) {

tests/testthat/test-write.R

@@ -183,6 +183,13 @@ test_that("hms NAs are written without padding (#930)", {
   expect_equal(format_tsv(df), "x\nNA\n00:00:34.234\n")
 })
 
+test_that("Show column name in error message when writing list column (#938)", {
+  df <- data.frame(x = LETTERS[1:4],
+                   y = I(list(1, "foo", 2:9, iris)))
+  expect_error(write_csv(df, "test_list_col_name.csv"),
+               "Don't know how to handle vector of type list in column 'y'.")
+})
+
 test_that("More helpful error when trying to write out data frames with list columns (#938)", {
   df <- tibble::tibble(id = seq(1), list = list(1))
   expect_error(write_csv(x = df, file = tempfile()), "Flat files can't store the list column")