bug#64596: 30.0.50; On FIXME: in src/buffer.c:1481 (force-mode-line-update)

[Stefan Monnier]

> So it sounds like we should make sure we don't set the frame's
> redisplay flag unless most or all of its windows actually need to be
> considered.  Is this so with the current code?

Indeed, the frame's `redisplay` bit means "*all* windows in that frame
need to be redisplayed", so it should be set with care.  But since the
code before that only had a single boolean for "redisplay all windows on
all frames", I was often happy enough to replace the global redisplay with
`fset_redisplay` even though it might be possible to be more specific.

`fset_redisplay` is typically used when windows are added/deleted/resized,
because it's hard at that point to know which windows really need to
be updated.


        Stefan