builtin: improve multi-platform portability for string.split_into_lines() (#17078)

vlib/builtin/js/string.js.v

@@ -792,7 +792,7 @@ pub fn (s string) split_into_lines() []string {
 	if s.len == 0 {
 		return res
 	}
-	#res.arr.arr = s.str.split("\n")
+	#res.arr.arr = s.str.split(/\r?\n|\r/)
 	#if (res.arr.arr[res.arr.arr.length-1] == "") res.arr.arr.pop();
 	#res.arr.len = new int(res.arr.arr.length);
 	#res.arr.cap = new int(res.arr.arr.length);

vlib/builtin/js/string_test.js.v

@@ -791,10 +791,18 @@ fn filter(b u8) bool {
 	return b != `a`
 }
 
-/*
 fn test_split_into_lines() {
-	line_content := 'Line'
-	text_crlf := '$line_content\r\n$line_content\r\n$line_content'
+	line_content := 'line content'
+
+	text_cr := '${line_content}\r${line_content}\r${line_content}'
+	lines_cr := text_cr.split_into_lines()
+
+	assert lines_cr.len == 3
+	for line in lines_cr {
+		assert line == line_content
+	}
+
+	text_crlf := '${line_content}\r\n${line_content}\r\n${line_content}'
 	lines_crlf := text_crlf.split_into_lines()
 
 	assert lines_crlf.len == 3
@@ -802,15 +810,31 @@ fn test_split_into_lines() {
 		assert line == line_content
 	}
 
-	text_lf := '$line_content\n$line_content\n$line_content'
+	text_lf := '${line_content}\n${line_content}\n${line_content}'
 	lines_lf := text_lf.split_into_lines()
 
 	assert lines_lf.len == 3
 	for line in lines_lf {
 		assert line == line_content
 	}
+
+	text_mixed := '${line_content}\n${line_content}\r${line_content}'
+	lines_mixed := text_mixed.split_into_lines()
+
+	assert lines_mixed.len == 3
+	for line in lines_mixed {
+		assert line == line_content
 	}
-*/
+
+	text_mixed_trailers := '${line_content}\n${line_content}\r${line_content}\r\r\r\n\n\n\r\r'
+	lines_mixed_trailers := text_mixed_trailers.split_into_lines()
+
+	assert lines_mixed_trailers.len == 9
+	for line in lines_mixed_trailers {
+		assert (line == line_content) || (line == '')
+	}
+}
+
 fn test_string_literal_with_backslash() {
 	a := 'HelloWorld'
 	assert a == 'HelloWorld'

vlib/builtin/string.v

@@ -841,22 +841,34 @@ pub fn (s string) split_nth(delim string, nth int) []string {
 
 // split_into_lines splits the string by newline characters.
 // newlines are stripped.
-// Both `\n` and `\r\n` newline endings are supported.
+// `\r` (MacOS), `\n` (POSIX), and `\r\n` (WinOS) line endings are all supported (including mixed line endings).
+// NOTE: algorithm is "greedy", consuming '\r\n' as a single line ending with higher priority than '\r' and '\n' as multiple endings
 [direct_array_access]
 pub fn (s string) split_into_lines() []string {
 	mut res := []string{}
 	if s.len == 0 {
 		return res
 	}
-	mut start := 0
+	cr := `\r`
+	lf := `\n`
+	mut line_start := 0
 	for i := 0; i < s.len; i++ {
-		if s[i] == 10 {
-			res << if start == i { '' } else { s[start..i].trim_right('\r') }
-			start = i + 1
+		if line_start <= i {
+			if s[i] == lf {
+				res << if line_start == i { '' } else { s[line_start..i] }
+				line_start = i + 1
+			} else if s[i] == cr {
+				res << if line_start == i { '' } else { s[line_start..i] }
+				if ((i + 1) < s.len) && (s[i + 1] == lf) {
+					line_start = i + 2
+				} else {
+					line_start = i + 1
 				}
 			}
-	if start < s.len {
-		res << s[start..]
+		}
+	}
+	if line_start < s.len {
+		res << s[line_start..]
 	}
 	return res
 }

vlib/builtin/string_test.v

@@ -883,7 +883,16 @@ fn filter(b u8) bool {
 }
 
 fn test_split_into_lines() {
-	line_content := 'Line'
+	line_content := 'line content'
+
+	text_cr := '${line_content}\r${line_content}\r${line_content}'
+	lines_cr := text_cr.split_into_lines()
+
+	assert lines_cr.len == 3
+	for line in lines_cr {
+		assert line == line_content
+	}
+
 	text_crlf := '${line_content}\r\n${line_content}\r\n${line_content}'
 	lines_crlf := text_crlf.split_into_lines()
 
@@ -899,6 +908,22 @@ fn test_split_into_lines() {
 	for line in lines_lf {
 		assert line == line_content
 	}
+
+	text_mixed := '${line_content}\n${line_content}\r${line_content}'
+	lines_mixed := text_mixed.split_into_lines()
+
+	assert lines_mixed.len == 3
+	for line in lines_mixed {
+		assert line == line_content
+	}
+
+	text_mixed_trailers := '${line_content}\n${line_content}\r${line_content}\r\r\r\n\n\n\r\r'
+	lines_mixed_trailers := text_mixed_trailers.split_into_lines()
+
+	assert lines_mixed_trailers.len == 9
+	for line in lines_mixed_trailers {
+		assert (line == line_content) || (line == '')
+	}
 }
 
 fn test_string_literal_with_backslash() {