Subject: bug#10117: duplicate evaluation of after-change-functions hooks in revert-buffer

From: Tiphaine Turpin <[email-masked]>
Date: Wed, 23 Nov 2011 12:18:15 +0100

Hi,

I'm having a strange behavior while trying to track the modifications to 
a buffer: calling revert-buffer triggers the following calls to my 
after-change-functions hook
- a region deletion (which is exactly the changed region between the 
buffer and the file)
- a region insertion (the new contents for the changed region)
- the same insertion again.
I don't care about how many modifications the reverting is splited into, 
or whether these are minimal or all the buffer contents is considered 
new, but the duplicate insertion leads me into invalid assumptions about 
the new contents (I use this to maintain a exact mapping of the buffer 
into an external tool).

Am I wrong when I assume that the sequence of modifications passed to 
the after-change-functions is an exact trace of the buffer contents 
evolution ? What could possibly cause such a duplicate event ?

Note: I'm not doing anything strange in the hook like changing the 
buffers' contents. This is just a numeric computation which update some 
buffer-local variables which track the set of "unprocessed" 
modifications. The hook is added as buffer-local (and global value of 
after-change-functions is nil).

Regards,

Tiphaine Turpin