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.

2 files changed, 64 insertions, 10 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);
diff --git a/src/xdisp.c b/src/xdisp.c
index 6d9acecb424..dc23959aadb 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -25123,7 +25123,20 @@ else if the text is replaced by an ellipsis.  */)
      '(space :width (+ left-fringe left-margin (- (1))))
      '(space :width (+ left-fringe left-margin (-1)))
 
-*/
+   If ALIGN_TO is NULL, returns the result in *RES.  If ALIGN_TO is
+   non-NULL, the value of *ALIGN_TO is a window-relative pixel
+   coordinate, and *RES is the additional pixel width from that point
+   till the end of the stretch glyph.
+
+   WIDTH_P non-zero means take the width dimension or X coordinate of
+   the object specified by PROP, WIDTH_P zero means take the height
+   dimension or the Y coordinate.  (Therefore, if ALIGN_TO is
+   non-NULL, WIDTH_P should be non-zero.)
+
+   FONT is the font of the face of the surrounding text.
+
+   The return value is non-zero if width or height were successfully
+   calculated, i.e. if PROP is a valid spec.  */
 
 static bool
 calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
@@ -25145,6 +25158,7 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
         {
           char *unit = SSDATA (SYMBOL_NAME (prop));
 
+          /* The UNIT expression, e.g. as part of (NUM . UNIT).  */
           if (unit[0] == 'i' && unit[1] == 'n')
             pixels = 1.0;
           else if (unit[0] == 'm' && unit[1] == 'm')
@@ -25165,10 +25179,12 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
         }
 
 #ifdef HAVE_WINDOW_SYSTEM
+      /* 'height': the height of FONT.  */
       if (EQ (prop, Qheight))
         return OK_PIXELS (font
                           ? normal_char_height (font, -1)
                           : FRAME_LINE_HEIGHT (it->f));
+      /* 'width': the width of FONT.  */
       if (EQ (prop, Qwidth))
         return OK_PIXELS (font
                           ? FONT_WIDTH (font)
@@ -25178,33 +25194,48 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
         return OK_PIXELS (1);
 #endif
 
+      /* 'text': the width or height of the text area.  */
       if (EQ (prop, Qtext))
           return OK_PIXELS (width_p
-                            ? window_box_width (it->w, TEXT_AREA)
+                            ? (window_box_width (it->w, TEXT_AREA)
+                               - it->lnum_pixel_width)
                             : WINDOW_BOX_HEIGHT_NO_MODE_LINE (it->w));
 
+      /* ':align_to'.  First time we compute the value, window
+         elements are interpreted as the position of the element's
+         left edge.  */
       if (align_to && *align_to < 0)
         {
           *res = 0;
+          /* 'left': left edge of the text area.  */
           if (EQ (prop, Qleft))
-            return OK_ALIGN_TO (window_box_left_offset (it->w, TEXT_AREA));
+            return OK_ALIGN_TO (window_box_left_offset (it->w, TEXT_AREA)
+                                + it->lnum_pixel_width);
+          /* 'right': right edge of the text area.  */
           if (EQ (prop, Qright))
             return OK_ALIGN_TO (window_box_right_offset (it->w, TEXT_AREA));
+          /* 'center': the center of the text area.  */
           if (EQ (prop, Qcenter))
             return OK_ALIGN_TO (window_box_left_offset (it->w, TEXT_AREA)
+                                + it->lnum_pixel_width
                                 + window_box_width (it->w, TEXT_AREA) / 2);
+          /* 'left-fringe': left edge of the left fringe.  */
           if (EQ (prop, Qleft_fringe))
             return OK_ALIGN_TO (WINDOW_HAS_FRINGES_OUTSIDE_MARGINS (it->w)
                                 ? WINDOW_LEFT_SCROLL_BAR_AREA_WIDTH (it->w)
                                 : window_box_right_offset (it->w, LEFT_MARGIN_AREA));
+          /* 'right-fringe': left edge of the right fringe.  */
           if (EQ (prop, Qright_fringe))
             return OK_ALIGN_TO (WINDOW_HAS_FRINGES_OUTSIDE_MARGINS (it->w)
                                 ? window_box_right_offset (it->w, RIGHT_MARGIN_AREA)
                                 : window_box_right_offset (it->w, TEXT_AREA));
+          /* 'left-margin': left edge of the left display margin.  */
           if (EQ (prop, Qleft_margin))
             return OK_ALIGN_TO (window_box_left_offset (it->w, LEFT_MARGIN_AREA));
+          /* 'right-margin': left edge of the right display margin.  */
           if (EQ (prop, Qright_margin))
             return OK_ALIGN_TO (window_box_left_offset (it->w, RIGHT_MARGIN_AREA));
+          /* 'scroll-bar': left edge of the vertical scroll bar.  */
           if (EQ (prop, Qscroll_bar))
             return OK_ALIGN_TO (WINDOW_HAS_VERTICAL_SCROLL_BAR_ON_LEFT (it->w)
                                 ? 0
@@ -25215,6 +25246,7 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
         }
       else
         {
+          /* Otherwise, the elements stand for their width.  */
           if (EQ (prop, Qleft_fringe))
             return OK_PIXELS (WINDOW_LEFT_FRINGE_WIDTH (it->w));
           if (EQ (prop, Qright_fringe))
@@ -25237,6 +25269,8 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
       int base_unit = (width_p
                        ? FRAME_COLUMN_WIDTH (it->f)
                        : FRAME_LINE_HEIGHT (it->f));
+      if (width_p && align_to && *align_to < 0)
+        return OK_PIXELS (XFLOATINT (prop) * base_unit + it->lnum_pixel_width);
       return OK_PIXELS (XFLOATINT (prop) * base_unit);
     }
 
@@ -25248,6 +25282,7 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
       if (SYMBOLP (car))
         {
 #ifdef HAVE_WINDOW_SYSTEM
+          /* '(image PROPS...)': width or height of the specified image.  */
           if (FRAME_WINDOW_P (it->f)
               && valid_image_p (prop))
             {
@@ -25256,12 +25291,15 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
 
               return OK_PIXELS (width_p ? img->width : img->height);
             }
+          /* '(xwidget PROPS...)': dimensions of the specified xwidget.  */
           if (FRAME_WINDOW_P (it->f) && valid_xwidget_spec_p (prop))
             {
               /* TODO: Don't return dummy size.  */
               return OK_PIXELS (100);
             }
 #endif
+          /* '(+ EXPR...)' or '(- EXPR...)' add or subtract
+             recursively calculated values.  */
           if (EQ (car, Qplus) || EQ (car, Qminus))
             {
               bool first = true;
@@ -25289,15 +25327,18 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
             car = Qnil;
         }
 
+      /* '(NUM)': absolute number of pixels.  */
       if (NUMBERP (car))
         {
           double fact;
+          int offset =
+            width_p && align_to && *align_to < 0 ? it->lnum_pixel_width : 0;
           pixels = XFLOATINT (car);
           if (NILP (cdr))
-            return OK_PIXELS (pixels);
+            return OK_PIXELS (pixels + offset);
           if (calc_pixel_width_or_height (&fact, it, cdr,
                                           font, width_p, align_to))
-            return OK_PIXELS (pixels * fact);
+            return OK_PIXELS (pixels * fact + offset);
           return false;
         }