csv: fix csv fields with double quotes (#10399)

vlib/encoding/csv/reader.v

@@ -145,7 +145,24 @@ fn (mut r Reader) read_record() ?[]string {
 			line = line[i + 1..]
 			continue
 		} else { // quoted
-			j := line[1..].index('"') or {
+			mut need_more := true
+			mut has_double_quotes := false
+			mut j := 0
+			mut n := 1
+			for n < line.len {
+				if line[n] == `"` {
+					if n == line.len - 1 || line[n + 1] != `"` {
+						need_more = false
+						j = n - 1
+						break
+					} else {
+						has_double_quotes = true
+						n++
+					}
+				}
+				n++
+			}
+			if need_more {
 				need_read = true
 				keep_raw = true
 				continue
@@ -153,12 +170,12 @@ fn (mut r Reader) read_record() ?[]string {
 			line = line[1..]
 			if j + 1 == line.len {
 				// last record
-				fields << line[..j]
+				fields << if has_double_quotes { line[..j].replace('""', '"') } else { line[..j] }
 				break
 			}
 			next := line[j + 1]
 			if next == r.delimiter {
-				fields << line[..j]
+				fields << if has_double_quotes { line[..j].replace('""', '"') } else { line[..j] }
 				if j + 2 == line.len {
 					line = ''
 				} else {

vlib/encoding/csv/reader_test.v

@@ -227,3 +227,27 @@ fn test_field_quotes_for_parts() {
 	}
 	assert row_count == 4
 }
+
+fn test_field_double_quotes() {
+	row1 := '11,"12\n13"\n'
+	row2 := '21,"2""2""\n23"\n'
+	row3 := '"3""1""",32\n'
+	data := row1 + row2 + row3
+	mut csv_reader := csv.new_reader(data)
+	mut row_count := 0
+	for {
+		row := csv_reader.read() or { break }
+		row_count++
+		if row_count == 1 {
+			assert row[0] == '11'
+			assert row[1] == '12\n13'
+		} else if row_count == 2 {
+			assert row[0] == '21'
+			assert row[1] == '2"2"\n23'
+		} else if row_count == 3 {
+			assert row[0] == '3"1"'
+			assert row[1] == '32'
+		}
+	}
+	assert row_count == 3
+}