Vim function somehow adds Ctrl-j to macro?

Question

I've written a short vim function that allows me to edit the contents of vim registers:

fun! RegBuff()
    let vimstuff = "/tmp/vimstuff"
    if !isdirectory(vimstuff)
        call mkdir(vimstuff)
    endif
    let reg = getchar()
    let reg = nr2char(reg)
    exec 'au BufWrite vimreg-* exec "normal gg0\"'.reg.'yy"'
    exec '1new '.vimstuff.'/vimreg-'.reg
    exec 'normal ggdG"'.reg.'P'
endfun
nnoremap <leader><F2> :call RegBuff()<CR>

If I do, for instance, qqi1234^[ to record insert 1234 into the q register, and then call my function :call RegBuff() or <leader><F2>, I get a nice little window at the top with the contents of the buffer. Cool. if I edit it to be i12345678^[, save the file and exit, and then do @q, it properly now enters insert mode and inserts 12345678. Also cool.

The problem is that I generally run vim in tmux, and for some reason after executing this macro it switches to the tmux pane below vim. This is as if the macro is additionally running <Ctrl>j after the macro is run.

If I go back to the vim pane, and type "qp to see whats in the q register it looks totally normal, it just contains what I expect to be in there.

Why does there appear to be this extra key code sent after I call the macro?

Answer 1

Came across this question is looking into a different ^J phenomenon.

Register Situation

In your RegBuff function, you yank text of the buffer into the register with yy. This is linewise yank, thus it appends the newline ^J to the register.

Printing the register ("qp) will not show the newline, but it will insert a line below cursor on which it prints the text. You can see the ^J explicitly by using the :reg {arg} command (:reg q shows the contents of q).

Solution

Change the linewise yank (yy -- yank line) to be a motion yank (y$ -- yank to end of line):

"Original linewise
exec 'au BufWrite vimreg-* exec "normal gg0\"'.reg.'yy"'

becomes

"Updated to motion
exec 'au BufWrite vimreg-* exec "normal gg0\"'.reg.'y$"'