Properly resize zsh prompt

resize-prompt.zsh

# It's not possible to properly resize a zsh prompt after the terminal changed
# it size. People think it's a hard to solve issue. See here:
# https://github.com/romkatv/powerlevel10k/issues/175. There're sollutions like
# patching the ZSH it self https://github.com/romkatv/zsh/tree/fix-winchanged
# but this is a total overkill.

# A far simpler solution is to save the old COLUMN value and on resize to
# calculate how many lines the prompt takes after reflow, move the cursor up
# that many lines and then draw your prompt.


# Example

add-zsh-hook precmd prompt-kalkin-precmd

OLD_COL=0

draw-my-prompt() {
    # DRAW THE PROMPT
}

prompt-kalkin-precmd() {
    PROMPT=$(draw-my-prompt)
    OLD_COL="$COLUMNS"
}

TRAPWINCH() {
    # calculate how many lines the prompt takes after terminal reflow
    local lines=$(( OLD_COL / COLUMNS ))
    [ $(( OLD_COL % COLUMNS )) != 0 ] && lines=$(( lines + 1))
    # move the cursor up
    echo -e "\033[s\033[${lines}A"

    PROMPT=$(draw-my-prompt)
    zle reset-prompt
    OLD_COL="$COLUMNS"
}