Treat missing values as length 0 when calculating user width (#701)

Close #699

NEWS.md

@@ -1,5 +1,8 @@
 # haven (development version)
 
+* Fix bug in string variable width calculation that treated `NA` values as width
+  2. `NA` values are now treated as blanks for width calculations (#699).
+
 # haven 2.5.1
 
 * All `labelled()` vectors now have left-aligned column headers when printing

src/DfWriter.cpp

@@ -19,6 +19,14 @@ inline const bool string_is_missing(SEXP x, int i) {
   return STRING_ELT(x, i) == NA_STRING;
 }
 
+inline const int string_len_missing(SEXP x, int i) {
+  if (string_is_missing(x, i)) {
+    return 0;
+  } else {
+    return strlen(string_utf8(x, i));
+  }
+}
+
 
 inline readstat_measure_e measureType(SEXP x) {
   if (Rf_inherits(x, "ordered")) {
@@ -366,7 +374,7 @@ class Writer {
     int user_width = userWidth(x);
     int max_length = 1;
     for (int i = 0; i < x.size(); ++i) {
-      int length = strlen(string_utf8(x, i));
+      int length = string_len_missing(x, i);
       if (length > max_length)
         max_length = length;
     }

tests/testthat/_snaps/haven-sas.md

@@ -6,3 +6,11 @@
       Error:
       ! Failed to create file: A provided name contains an illegal character.
 
+# user width warns appropriately when data is wider than value
+
+    Code
+      write_xpt(df, path)
+    Condition
+      Warning:
+      Column `b` contains string values longer than user width 1. Width set to 2 to accommodate.
+

tests/testthat/test-haven-sas.R

@@ -274,3 +274,15 @@ test_that("can roundtrip format attribute", {
 
   expect_identical(df, out)
 })
+
+test_that("user width warns appropriately when data is wider than value", {
+  df <- tibble(
+    a = c("a", NA_character_),
+    b = c("b", "NA"),
+  )
+  attr(df$a, "width") <- 1
+  attr(df$b, "width") <- 1
+
+  path <- tempfile()
+  expect_snapshot(write_xpt(df, path))
+})