GH-33432: [R] Match base/stringr semantics for str_replace() with NA replacement

r/R/dplyr-funcs-string.R

@@ -367,6 +367,26 @@ register_bindings_string_regex <- function() {
       if (length(replacement) != 1) {
         validation_error("`replacement` must be a length 1 character vector")
       }
+      # An NA replacement sets the whole string to NA wherever the pattern
+      # matches, matching base::sub()/gsub() and stringr::str_replace(). The
+      # replace_substring[_regex] kernels don't support this, so rewrite it as
+      # if_else(<pattern matches>, NA, x). GH-33432
+      if (is.na(replacement)) {
+        is_match <- Expression$create(
+          ifelse(fixed && !ignore.case, "match_substring", "match_substring_regex"),
+          x,
+          options = list(
+            pattern = format_string_pattern(pattern, ignore.case, fixed),
+            ignore_case = FALSE
+          )
+        )
+        return(Expression$create(
+          "if_else",
+          is_match,
+          Expression$scalar(NA_character_),
+          x
+        ))
+      }
       Expression$create(
         ifelse(fixed && !ignore.case, "replace_substring", "replace_substring_regex"),
         x,

r/tests/testthat/test-dplyr-funcs-string.R

@@ -428,6 +428,33 @@ test_that("sub and gsub with namespacing", {
   )
 })
 
+test_that("str_replace/sub with an NA replacement match base/stringr (GH-33432)", {
+  df <- tibble(x = c("", "one", "two", "three", "four", NA))
+
+  # A match sets the whole value to NA; non-matches and NA input are unchanged
+  compare_dplyr_binding(
+    .input |>
+      transmute(
+        regex = str_replace(x, "o", NA_character_),
+        regex_all = str_replace_all(x, "o", NA_character_),
+        fixed = str_replace_all(x, fixed("o"), NA_character_),
+        ci = str_replace_all(x, regex("O", ignore_case = TRUE), NA_character_)
+      ) |>
+      collect(),
+    df
+  )
+
+  compare_dplyr_binding(
+    .input |>
+      transmute(
+        subbed = sub("o", NA_character_, x),
+        gsubbed = gsub("o", NA_character_, x)
+      ) |>
+      collect(),
+    df
+  )
+})
+
 test_that("str_replace and str_replace_all", {
   x <- Expression$field_ref("x")