bug#6192: 24.0.50; eldoc-mode: unexpected recentering

[Stefan Monnier <monnier@iro.umontreal.ca>]

> In short, this bug now boils down to this: the echo area resizes with
> certain fonts (including DejaVu Sans Mono) when it displays a message
> that includes bold face.  Whether this is a bug in Emacs or the
> problematic fonts, I don't know.

To summarize this long thread, IIUC we have three separate problems:
- in some cases, a minibuffer message with bold text causes
  unexpected/unneeded minibuffer resizing.  Most likely those fonts
  somehow end up with a height just a tiny pixel taller.  Maybe we
  should change the minibuffer resizing such that it only resizes if the
  extra height needed is more than some threshold number of pixels (1
  or 2).
- eldoc can cause undesired minibuffer resizing.  That can probably still
  happen even when we fix the previous problem, depending on face
  settings and/or length of eldoc data.  So maybe eldoc should come with
  a config var for how many max lines of echo-area we're willing to
  devote to it.  If set to 1 it will prevent any resizing and fix the
  OP's problem regardless of whether the previous problem is fixed.
- minibuffer auto-resize can trigger an undesirable recentering.
  I'm not sure we can do much about that, tho, since it seems to only
  occur in cases where the resizing ends up "eating" the area used by
  point, so some scrolling is necessary.


        Stefan