Why buffer_shared is a mistake

[Dmitry Antipov]

Look at the screenshot. Here 'A' is an overlay highlighted with 
font-lock-keyword-face
in buffer *scratch*. What happens if I type C-x C-e (eval-last-sexp) staying  
where the
cursor is?

1) Redisplay is invoked with "xaxa" as current_buffer, and buffer_shared is 
recalculated
   to 2 because "xaxa" is displayed in 2 windows. On leaving 
redisplay_internal, buffer_shared
   is 2.

2) modify_overlay is called for "*scratch*", and this function still sees 
buffer_shared as 2
   (unchanged since last redisplay invocation), although *scratch* is displayed 
in the only
   window.

3) ???

IIUC, as the minimum minorum, buffer_shared should be reset to 0 after leaving 
redisplay_internal.
Or it should be a per-buffer field.

Dmitry

redisplay.png
Description: PNG image