viewport: last line of content not rendered when scrolling if it doesn't end with new line \n

[MarcoLucidi01]

hello, I come from a project (ticker) that uses bubbles/viewport to display its main contents.

we noticed that when the content doesn't fit on a single page and you scroll at the bottom, bubbles/viewport doesn't render the last line of content if it doesn't end with a new line \n character (here the issue #158 reported on ticker).

the problem is reproducible with bubbletea's pager example that uses bubbles/viewport, for example:

$ git clone https://github.com/charmbracelet/bubbletea.git
...
$ cd bubbletea/examples/pager/
$ go build
$ ls -1
artichoke.md    # file displayed in the example
main.go
pager*
$ tail -1 artichoke.md | xxd | tail -1
00000030: 2069 6e20 5370 616e 6973 682e 0a          in Spanish..    # ends with new line
$ ./pager

lastline.mp4

everything looks fine, now I remove last new line \n character from artichoke.md:

$ truncate -s -1 artichoke.md
$ tail -1 artichoke.md | xxd | tail -1
00000030: 2069 6e20 5370 616e 6973 682e             in Spanish.
$ ./pager

nolastline.mp4

and the last line

_Alcachofa_, if you were wondering, is artichoke in Spanish.

is not displayed anymore.

unfortunately I don't have a patch, I suspect it's an off-by-one error because I see lots of len(m.lines)-1 in viewport.go and I think it could be related to the problem, but I wasn't able to completely figure it out.

[meowgorithm]

Noted, thanks for the report. I suspect you’re right about the off-by-one error, but we’ll take a look.

[meowgorithm]

This is now fixed in master and will be available in the next release. Thank you very much for the thorough report!