builtin: rewrite string.split_nth and fix some bugs (#7189)

cmd/tools/vrepl.v

@@ -301,7 +301,7 @@ fn run_repl(workdir string, vrepl_prefix string) {
 }
 
 fn print_output(s os.Result) {
-	lines := s.output.trim_right('\n\r').split('\n')
+	lines := s.output.trim_right('\n\r').split_into_lines()
 	for line in lines {
 		if line.contains('.vrepl_temp.v:') {
 			// Hide the temporary file name

vlib/builtin/string.v

@@ -484,7 +484,7 @@ pub fn (s string) split_nth(delim string, nth int) []string {
 		i = 1
 		for ch in s {
 			if nth > 0 && i >= nth {
-				res << s.substr(i, s.len)
+				res << s.right(i)
 				break
 			}
 			res << ch.str()
@@ -493,39 +493,30 @@ pub fn (s string) split_nth(delim string, nth int) []string {
 		return res
 	}
 	mut start := 0
-	nth_1 := nth - 1
+	// Take the left part for each delimiter occurence
 	for i <= s.len {
-		mut is_delim := unsafe {s.str[i] == delim.str[0]}
-		mut j := 0
-		for is_delim && j < delim.len {
-			is_delim = is_delim && unsafe {s.str[i + j] == delim.str[j]}
-			j++
-		}
-		last := i == s.len - 1
-		if is_delim || last {
-			if !is_delim && last {
-				i++
-			}
-			mut val := s.substr(start, i)
-			if val.starts_with(delim) {
-				val = val.right(delim.len)
-			}
-			was_last := nth > 0 && res.len == nth_1
+		is_delim := i + delim.len <= s.len && s.substr(i, i + delim.len) == delim
+		if is_delim {
+			val := s.substr(start, i)
+			was_last := nth > 0 && res.len == nth - 1
 			if was_last {
-				res << s.right(start)
 				break
 			}
 			res << val
 			start = i + delim.len
+			i = start
+		} else {
+			i++
 		}
-		i++
 	}
-	if s.ends_with(delim) && (nth < 1 || res.len < nth) {
-		res << ''
+	// Then the remaining right part of the string
+	if nth < 1 || res.len < nth {
+		res << s.right(start)
 	}
 	return res
 }
 
+
 pub fn (s string) split_into_lines() []string {
 	mut res := []string{}
 	if s.len == 0 {

vlib/builtin/string_test.v

@@ -138,8 +138,8 @@ fn test_split_nth() {
 	assert (d.split_nth(',', -1).len == 2)
 	assert (d.split_nth(',', 3).len == 2)
 	e := ",,,0,,,,,a,,b,"
-	// assert (e.split(',,').len == 5)
-	// assert (e.split_nth(',,', 3).len == 2)
+	assert (e.split(',,').len == 5)
+	assert (e.split_nth(',,', 3).len == 3)
 	assert (e.split_nth(',', -1).len == 12)
 	assert (e.split_nth(',', 3).len == 3)
 }
@@ -213,6 +213,12 @@ fn test_split() {
 	assert a[4] == 'o'
 	assert a[5] == 'm'
 	assert a[6] == 'e'
+	// /////////
+	s = 'wavy turquoise bags'
+	vals = s.split(' bags')
+	assert vals.len == 2
+	assert vals[0] == 'wavy turquoise'
+	assert vals[1] == ''
 }
 
 fn test_trim_space() {