On 11/28/15 18:09, Dmitry Gutov wrote:
> Please try this definition and see if it resolves the problem:
>
> (defun vc-hg-previous-revision (_file rev)
>   (let ((newrev (1- (string-to-number rev))))
>     (when (>= newrev 0)
>       (with-temp-buffer
>         (vc-hg-command t 0 nil
>                        "id" "--hidden" "-n" "-r"
>                        (format "first(%d:0 and not hidden())" newrev))
>         ;; Trim the trailing newline.
>         (buffer-substring (point-min) (1- (point-max)))))))
>
>> This says to look at all non-hidden revs from X down to zero, choose the
>> first one, and print its numeric rev number.  If the current rev is X+1,
>> that gives the first previous non-hidden rev.  But I'm sure there must
>> be a better way, without having to examine all previous changesets.
>
> If you anticipated that we'd have to make one process call per 
> revision, then I think the above definition does better.
I tried this, and it works fine.  But I discovered another problem for 
VC with the changeset evolution features: if a repository has any 
changesets that are marked 'obsolete', and any mercurial command is 
issued by a user who hasn't enabled the extension, a warning message is 
printed to stderr:

    obsolete feature not enabled but <N> markers found!

If VC grabs this output as part of the mercurial response, and uses it 
in subsequent commands, it (unsurprisingly) fails:

    hg: parse error at 9: invalid token

Looking at mercurial sources, there's no way to suppress this warning.  
I guess one workaround would be to have vc-hg-command skip over it if 
it's there.

Glenn