Support writing linear-tsv-style with escape="sep"

Author: dvg-p4

R/vroom_write.R

@@ -5,6 +5,7 @@
 #' @param escape The type of escape to use when quotes are in the data.
 #'   - `double` - quotes are escaped by doubling them.
 #'   - `backslash` - quotes are escaped by a preceding backslash.
+#'   - `sep` - tabs, newlines, and backslashes are escaped as `\t`, `\n`, and `\\`
 #'   - `none` - quotes are not escaped.
 #' @param quote How to handle fields which contain characters that need to be
 #'   quoted.
@@ -37,7 +38,7 @@
 #' # vroom_write(mtcars, "mtcars.tsv.xz")
 vroom_write <- function(x, file, delim = '\t', eol = "\n", na = "NA", col_names = !append,
   append = FALSE, quote = c("needed", "all", "none"), escape =
-    c("double", "backslash", "none"), bom = FALSE, num_threads =
+    c("double", "backslash", "sep", "none"), bom = FALSE, num_threads =
     vroom_threads(), progress = vroom_progress(), path = deprecated()) {
 
   if (lifecycle::is_present(path)) {
@@ -53,6 +54,15 @@ vroom_write <- function(x, file, delim = '\t', eol = "\n", na = "NA", col_names
   quote <- match.arg(quote)
   escape <- match.arg(escape)
 
+  if (escape == "sep") {
+    if (!all(c(delim, eol) %in% c("\t", "\n", "\r", "\r\n"))) {
+      stop("Can only escape separators `\\t`, `\\n`, and `\\r`")
+    }
+    if (quote != "none") {
+      warning("quotes in data will not be escaped with `escape = sep`")
+    }
+  }
+
   opts <- get_vroom_write_opts(quote, escape, bom)
 
   # Standardise path returns a list, but we will only ever have 1 output file.
@@ -109,7 +119,8 @@ vroom_write_opts <- function() c(
   "quote_all" = 2L,
   "escape_double" = 4L,
   "escape_backslash" = 8L,
-  "bom" = 16L
+  "bom" = 16L,
+  "escape_sep" = 32L
 )
 
 #' Convert a data frame to a delimited string
@@ -121,7 +132,7 @@ vroom_write_opts <- function() c(
 #' @inheritParams vroom_write
 #' @export
 vroom_format <- function(x, delim = "\t", eol = "\n", na = "NA", col_names = TRUE,
-                         escape = c("double", "backslash", "none"),
+                         escape = c("double", "backslash", "sep", "none"),
                          quote = c("needed", "all", "none"),
                          bom = FALSE,
                          num_threads = vroom_threads()) {
@@ -135,6 +146,15 @@ vroom_format <- function(x, delim = "\t", eol = "\n", na = "NA", col_names = TRU
   quote <- match.arg(quote)
   escape <- match.arg(escape)
 
+  if (escape == "sep") {
+    if (!all(c(delim, eol) %in% c("\t", "\n", "\r", "\r\n"))) {
+      stop("Can only escape separators `\\t`, `\\n`, and `\\r`")
+    }
+    if (quote != "none") {
+      warning("quotes in data will not be escaped with `escape = sep`")
+    }
+  }
+
   opts <- get_vroom_write_opts(quote, escape, bom)
 
   # This seems to work ok in practice

src/vroom_write.cc

@@ -20,7 +20,8 @@ typedef enum {
   quote_all = 2,
   escape_double = 4,
   escape_backslash = 8,
-  bom = 16
+  bom = 16,
+  escape_sep = 32
 } vroom_write_opt_t;
 
 size_t get_buffer_size(
@@ -135,16 +136,41 @@ void str_to_buf(
   }
 
   auto end = str_p + len;
-  bool should_escape = options & (escape_double | escape_backslash);
-  auto escape =
-      options & escape_double ? '"' : options & escape_backslash ? '\\' : '\0';
-
   buf.reserve(buf.size() + len);
-  while (str_p < end) {
-    if (should_escape && *str_p == '"') {
-      buf.push_back(escape);
+
+  if (options & escape_sep) {
+    while (str_p < end) {
+      if (*str_p == '\t') {
+        buf.push_back('\\');
+        buf.push_back('t');
+        ++str_p;
+      } else if (*str_p == '\n') {
+        buf.push_back('\\');
+        buf.push_back('n');
+        ++str_p;
+      } else if (*str_p == '\r') {
+        buf.push_back('\\');
+        buf.push_back('r');
+        ++str_p;
+      } else if (*str_p == '\\') {
+        buf.push_back('\\');
+        buf.push_back('\\');
+        ++str_p;
+      } else {
+        buf.push_back(*str_p++);
+      }
+    }
+  } else {
+    bool should_escape = options & (escape_double | escape_backslash);
+    auto escape =
+        options & escape_double ? '"' : options & escape_backslash ? '\\' : '\0';
+
+    while (str_p < end) {
+      if (should_escape && *str_p == '"') {
+        buf.push_back(escape);
+      }
+      buf.push_back(*str_p++);
     }
-    buf.push_back(*str_p++);
   }
 
   if (should_quote) {