Add append support for CSVWriter

[jsm174]

Hello. I was looking to have a CSV file that gets updated every time a user performs an action in an app. I also wanted the CSV file to contain a header row.

Subsequent appends won't be started on a new line because isFirstRow is defaulted to true, causing write to ignore the configuration.newline.unicodeScalars.forEach(writeScalar) call.

I thought I could just add a beginNewRow() call, but it technically doesn't modify the steam

Here is the code I was trying:

           let exists = FileManager.default.fileExists(atPath: url.path)
           
           let stream = OutputStream(url: url, append: true)!
           let csv = try! CSVWriter(stream: stream)
           
           if !exists {
               try! csv.write(row: ["Date", "Question 1", "Question 2", "Question 3"])
           }

           try! csv.write(row: [rfcDate, answer1, answer2, answer3])

           csv.stream.close()

[jsm174]

Until (or if ever) there is a fix, I've worked around by adding the new line directly to stream:

            let exists = FileManager.default.fileExists(atPath: url.path)
            
            let stream = OutputStream(url: url, append: true)!
            let csv = try! CSVWriter(stream: stream)
            
            if !exists {
                try! csv.write(row: ["Date", "Question 1", "Question 2", "Question 3"])
            }
            
            let rfcDate = Date().rfcString()
                        
            try! csv.write(row: [rfcDate, question1Answer, question2Answer, question3Answer])
            
            let data = [UInt8](csv.configuration.newline.utf8)
            csv.stream.write(data, maxLength: data.count)
            
            csv.stream.close()

[wizofaus]

Is it normal in a MacOS environment for CSV files NOT to be newline terminated?
I'm used to expecting CSV files to end with a newline (or CRLF), so if I created an OutputStream on such a file, this library would correctly append new lines - but leave me with a stream that no longer ends with a newline and hence require, as you do above, manually adding one before appending further lines.
If there really is a need to produce CSV files that aren't newline terminated, I suppose it could be an option (but I'd expect it to do by default).