bug#20687: 25.0.50; `perform-replace' should invoke a key that you have bound in `query-replace-map'

[Drew Adams]

> I tested this out and the M-c and M-r bindings work great. It now
> also gives clear info on what the user should expect after that
> binding is used. Please give it a try. I have still kept this line
> 
>  (def (call-interactively def)) ; User-defined key, invoke it.
> 
> as it could be useful to bind any other function from outside
> that does not need internal variables.

1. I'm OK with whatever you guys come up with.  Thanks for working
   on this.

2. I tried it only a little.  When I tried `M-r':

   * If the replacement string had uppercase chars then I always
     got the same message, which was very long - too long to read
     in the short time it was displayed.  Could we shorten that
     message, please?  And could we maybe have it logged to
     *Messages*, so that if someone doesn't have time to read it
     s?he can look it up?

   * If the replacement string had no uppercase chars then I always
     got the same message (about case-fold-search being nil).

   What is `M-r' really supposed to do?  I don't see how it is a
   toggle, if repeating it always gives the same message, given
   the same replacement string.  Can you describe what the toggling
   or cycling among states is supposed to do/mean?

3. Wrt this: 

      I have still kept this line
      (def (call-interactively def)) ; User-defined key, invoke it.
      as it could be useful to bind any other function from outside
      that does not need internal variables.

   I think Juri is right, that it should be the following, because
   `lookup-key' can return a number if the key is too long:

   ((commandp def t)          ; User-defined key, invoke it.
    (call-interactively def))

4. If one of you could replace the paragraphs of the doc that I
   mentioned by just a statement that search is controlled by
   `case-fold-search', that would be good. You could then add
   that you can toggle this using `M-c' etc. IOW, (1) those
   paragraphs are useless, and (2) now we have something more
   to say about case sensitivity.