Support cons cell for 'line-spacing'

* etc/NEWS: Announce the change.
* src/dispextern.h (struct glyph_row): Add
'extra_line_spacing_above' member.
(struct it): Add 'extra_line_spacing_above' member.
* src/frame.h (struct frame): Add 'extra_line_spacing_above'
member.  Update comment for 'extra_line_spacing.'
* src/buffer.c (syms_of_buffer): Update the docstring of
'line-spacing' to describe the cons cell usage.
* src/buffer.h (struct buffer): Update comment for
'extra_line_spacing'.
* src/frame.c (gui_set_line_spacing): Handle cons cell value for
'line-spacing'.  Calculate and set 'extra_line_spacing_above'
for both integer and float pairs.
* src/xdisp.c (init_iterator): Initialize 'extra_line_spacing_above'
from buffer or frame 'line-spacing', handling cons cells for both
integer and float values.
(gui_produce_glyphs): Use 'extra_line_spacing_above' to distribute
spacing between ascent and descent.  Update 'max_extra_line_spacing'
calculation.
(resize_mini_window): Take line spacing into account when resizing the
mini window.  Pass height of a single line to 'grow_mini_window' and
'shrink_mini_window'.
* src/window.c (grow_mini_window, shrink_mini_window): Add unit
argument which defines height of a single line.
* src/window.h (grow_mini_window, shrink_mini_window): Adjust function
prototypes accordingly with unit argument.
* lisp/subr.el (total-line-spacing): New function to calculate total
spacing from a number or cons cell.
(posn-col-row): Use total-line-spacing.
* lisp/simple.el (default-line-height): Use 'total-line-spacing'.
* lisp/textmodes/picture.el (picture-mouse-set-point): Use
'total-line-spacing'.
* lisp/window.el (window-default-line-height): Use
'total-line-spacing'.
(window--resize-mini-window): Take 'line-spacing' into account.
* test/lisp/subr-tests.el (total-line-spacing): New test.
* test/src/buffer-tests.el (test-line-spacing): New test.
* doc/emacs/display.texi (Display Custom): Document that
'line-spacing' can be a cons cell.
(Line Height): Document the new cons cell format for 'line-spacing'
to allow vertical centering.

Co-authored-by: Przemysław Alexander Kamiński <alexander@kaminski.se>
Co-authored-by: Daniel Mendler <mail@daniel-mendler.de>

1 files changed, 18 insertions, 0 deletions

diff --git a/test/src/buffer-tests.el b/test/src/buffer-tests.el
index 9ed76a42603..5f534ed513a 100644
--- a/test/src/buffer-tests.el
+++ b/test/src/buffer-tests.el
@@ -8650,4 +8650,22 @@ Finally, kill the buffer and its temporary file."
     (should (= (point-min) 1))
     (should (= (point-max) 5001))))
 
+(ert-deftest test-line-spacing ()
+  "Test `line-spacing' impact on text size"
+  (skip-unless (display-graphic-p))
+  (let*
+      ((size-with-text (lambda (ls)
+                         (with-temp-buffer
+                           (setq-local line-spacing ls)
+                           (insert "X\nX")
+                           (cdr (buffer-text-pixel-size))))))
+    (cl-loop for x from 0 to 50
+             for y from 0 to 50
+             do
+             (ert-info ((format "((linespacing '(%d . %d)) == (linespacing %d)" x y (+ x y))
+                        :prefix "Linespace check: ")
+               (should (=
+                        (funcall size-with-text (+ x y))
+                        (funcall size-with-text (cons x y))))))))
+
 ;;; buffer-tests.el ends here