Re: flyspell bug

["Eli Zaretskii" <eliz@gnu.org>]

> From: Juri Linkov <juri@jurta.org>
> Date: Wed, 11 May 2005 11:23:48 +0300
> 
> ispell and aspell use different dictionaries.  Changing the default
> ispell program name from "ispell" to "aspell" is an incompatible
> change for users configured Emacs to use ispell dictionaries,
> not aspell dictionaries.

I understand that.  What I need is a way to distinguish between three
situations:

  (1) user doesn't have aspell installed
  (2) user has aspell installed, but configured it to use ispell's
      dictionaries
  (3) user has aspell installed and wants to use aspell's dictionaries

I know how to detect (1) -- use locate-file or similar technique to
look for aspell.  But how to distinguish between (2) and (3)?

> `ispell-program-name' can be changed
> automatically to "aspell" only when `ispell-check-version' detects
> aspell's implemention of ispell, i.e. a program for which `ispell -v'
> returns:
> 
> @(#) International Ispell Version 3.1.20 (but really Aspell 0.50.5)

So the conditions for (2) should be:

  (a) locate-file finds an executable `ispell'
  (b) that `ispell', when invoked with -v outputs the above banner

Is that right?  Are we sure that no user will use aspell with ispell's
dictionaries _except_ through the `ispell' alias?