Re: History for query replace pairs

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@jurta.org>
> Cc: emacs-devel@gnu.org
> Date: Sat, 08 Nov 2014 12:29:41 +0200
> 
> > I briefly tried it (will do more testing once NEWS or the manual
> 
> It's too early to describe it in the manual because it might require
> more changes after testing.  And to announce it in NEWS we need
> something more substantial such as to add an option to enable/disable
> this feature.

I'm okay with delaying the changes in the manual, but as for NEWS, you
cannot expect people who track the trunk to start using something
about which they have no hints at all.  At the very least, post some
initial information here.  Also, NEWS can explain features that have
no expression at all in user-level options; as long as there are
user-visible changes in behavior or keybindings or their meaning, this
is definitely NEWS-worthy stuff.

> > describes the feature in detail), and saw one problem: the Unicode
> > character → (u+2192) is a problem on TTYs that can't encode it or on
> > GUI frames that use font without a glyph for it.  So I think we need a
> > fallback for those cases (e.g., using char-displayable-p to detect them).
> 
> When I tried to use char-displayable-p in defcustom, then
> bootstraping failed with the error
> 
>   Attempt to autoload char-displayable-p while preparing to dump
> 
> because replace.el is preloaded, and we don't know whether the character
> will be displayable on the current display.

You could do that test only in interactive calls, or check
purify-flag, to avoid calling the function while dumping.

> I wonder is it possible to detect undisplayable characters in the
> display engine and perform the normalization using the rules
> for confusable characters?

It's possible, but I don't think we have such a feature now.

> In lisp/international/latin1-disp.el in latin1-display-ucs-per-lynx I see
> the mapping (?\→ "->").  Could it be used for an automatic fallback?

Used how?  Applying those large display tables sounds like a
misfeature to me: Emacs shouldn't do that without user's say-so, IMO.
If you mean something else, please elaborate.