bug#21932: 24.3.1; tabulated-list-mode minor bugs and feature requests

[Ken Raeburn]

Tabulated list mode is quite a nice helper for viewing information.  I’ve used 
it to throw together various simple modes for debugging other Emacs code or for 
work — listing Emacs timers, listing Emacs frames and which displays they’re 
on, listing my Perforce workspaces with descriptions.

In using it, I have run across a few minor issues, and have a few enhancements 
I’d like to see.

1) Tabulated list mode doesn’t line the columns up properly if you use C-x C— 
or C-x C-+ to alter the text size.  The columns are not lined up consistently, 
though in the mode I’m writing right now, some of them do seem to stay lined up 
with the headers if I shrink the text.

2) When changing the text size, the text of the header line is unchanged.  If 
this is intentional, then the number of characters in each column should be 
adjusted up or down to compensate, so that entry columns aren’t too wide, and 
aren’t truncated to a much narrower width than necessary.  I would guess it’s 
accidental, though.

3) Tabulated list mode doesn’t line the columns up properly if you use 
variable-pitch-mode.  This one is hard, I’m sure, because the same buffer could 
simultaneously be displayed on multiple displays that support different fonts, 
and on terminals that don’t support anything but one fixed-width font.  If we 
don’t truncate each string to the shortest length useable across all frames 
displaying the buffer based on font metrics and the specific text to be 
displayed, which would probably look kind of ugly (…but might not?), then I 
think we need the display engine to make the choice where to truncate rather 
than the Lisp code.

4) On most graphical displays it should be capable of using the Unicode 
ellipsis code point U+2026 instead of taking up three columns with dots; that 
would give us back two columns of text on such displays.  Again, this would be 
potentially displaying different amounts of text, as well as different 
ellipses, on different displays.

5) Adjustable column widths: Many table-based GUIs I’ve seen let the user grab 
the dividing line between headers and drag it left or right to alter a field’s 
width, sometimes with limits to how wide or narrow the field is allowed to be.  
It wouldn’t work for every case, but when there is a padding space between 
column headers, perhaps it can be given mouse bindings similar to the way 
mouse-drag-vertical-line works.

Ken