Make :align-to account for display-line-numbers

These changes also update the various bundled packages to use
new feature, and better support customizations of the line-number
face.
* src/xdisp.c (calc_pixel_width_or_height): Improve commentary.
Make :align-to count from the end of the line-number display when
the offset or the width form reference that of the text area.
(Bug#28855)

* src/indent.c (Fline_number_display_width): Implement support for
the PIXELWISE argument being 'columns'.  Update the doc string.
(syms_of_indent): New symbol 'columns'.

* lisp/ruler-mode.el (ruler-mode-window-col, ruler-mode-ruler):
Call line-number-display-width with last argument 'columns'.

* lisp/proced.el (proced-header-line): Call
line-number-display-width with 2nd arg 'columns', which also fixes
a problem when display-line-numbers is nil.

* lisp/emacs-lisp/tabulated-list.el
(tabulated-list-line-number-width): Call line-number-display-width
with 2nd arg 'columns.
(tabulated-list-entry-lnum-width): Remove unneeded defvar.
(tabulated-list-print, tabulated-list-print-entry): No need to
account for the value of tabulated-list-entry-lnum-width.
(tabulated-list--current-lnum-width): New defvar.
(tabulated-list-watch-line-number-width): New function.
(tabulated-list-mode): Bind tabulated-list--current-lnum-width
locally, and set up tabulated-list-watch-line-number-width as
pre-redisplay-functions hook.

* doc/lispref/display.texi (Size of Displayed Text): Document the
'columns' value of the PIXELWISE argument.
(Pixel Specification): Update and improve the documentation of the
supported forms.

1 files changed, 18 insertions, 5 deletions

diff --git a/src/indent.c b/src/indent.c
index a3e9b5b0b9a..192eec72efe 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -1991,15 +1991,26 @@ line_number_display_width (struct window *w, int *width, int *pixel_width)
 DEFUN ("line-number-display-width", Fline_number_display_width,
        Sline_number_display_width, 0, 1, 0,
        doc: /* Return the width used for displaying line numbers in the selected window.
-If optional argument PIXELWISE is non-nil, return the width in pixels,
-otherwise return the width in columns of the face used to display
-line numbers, `line-number'.  Note that in the latter case, the value
-doesn't include the 2 columns used for padding the numbers.  */)
+If optional argument PIXELWISE is the symbol `columns', return the width
+in units of the frame's canonical character width.  In this case, the
+value is a float.
+If optional argument PIXELWISE is t or any other non-nil value, return
+the width as an integer number of pixels.
+Otherwise return the value as an integer number of columns of the face
+used to display line numbers, `line-number'.  Note that in the latter
+case, the value doesn't include the 2 columns used for padding the
+numbers on display.  */)
   (Lisp_Object pixelwise)
 {
   int width, pixel_width;
+  struct window *w = XWINDOW (selected_window);
   line_number_display_width (XWINDOW (selected_window), &width, &pixel_width);
-  if (!NILP (pixelwise))
+  if (EQ (pixelwise, Qcolumns))
+    {
+      struct frame *f = XFRAME (w->frame);
+      return make_float ((double) pixel_width / FRAME_COLUMN_WIDTH (f));
+    }
+  else if (!NILP (pixelwise))
     return make_number (pixel_width);
   return make_number (width);
 }
@@ -2361,6 +2372,8 @@ syms_of_indent (void)
                doc: /* Indentation can insert tabs if this is non-nil.  */);
   indent_tabs_mode = 1;
 
+  DEFSYM (Qcolumns, "columns");
+
   defsubr (&Scurrent_indentation);
   defsubr (&Sindent_to);
   defsubr (&Scurrent_column);