PerBothner
commented
8 years ago If we keep the "fresh-line" functionality, could we at least make it controlled by an Option? I can create a pull request either way: controlled by an option, or jusr remove the functionality.
gnodet
In LineReaderImpl's readLine method there is logic to "Make sure we position the cursor on column 0". (Search for a comment with that text.) I.e. do nothing if we're at column 0 but otherwise move to the start of the next line. (This is the CommonLisp "fresh-line" function.)
I believe this logic causes more problems than it solves. Most obviously, I'm confused by the use of "~". The actual "~" shows in the output (at least in my usage), which is obviously a problem.
If we replace the initial "~" by (one more) space, we get the desired effect. (Though only if thd terminal supports vt100-style line-wrap.) However, copy and paste is wrong because terminals (such as xterm) that keep track on line-wrapping think the previous line is wrapped.
With xterm and similar we can make use of a cursor position request and go to a new line unless the column is 0. This does require an extra round-trip to the terminal. I don't believe there is a terminfo capability for cursor position request, but checking TERM for "xterm" is probably good enough in practice.
My recommendation: Drop the entire functionality (it is not handled by GNU readline), and make "fresh-line" be the responsibility of the application, not jline. Concretely, remove the lines starting with "Make sure we position the cursor on column 0" and ending with "print(sb.toAnsi(terminal));".