window--resize-root-window-vertically

window--resize-root-window-vertically is a compiled Lisp function in `window.el'.

(window--resize-root-window-vertically WINDOW DELTA PIXELWISE)

Resize root window WINDOW vertically by DELTA lines.
If DELTA is less than zero and we can't shrink WINDOW by DELTA
lines, shrink it as much as possible. If DELTA is greater than
zero, this function can resize fixed-size windows in order to
recover the necessary lines. Return the number of lines that
were recovered.

Third argument PIXELWISE non-nil means to interpret DELTA as
pixels and return the number of pixels that were recovered.

This function is called by the minibuffer window resizing
routines.