Re: [PATCH v3 01/11] replace: forbid replacing an object with one of a different type

From: "Christian Couder" <redacted>

From: "Philip Oakley" <redacted>

quoted

Sorry for not replying earlier in the series.

From: "Christian Couder" <redacted>

quoted

Users replacing an object with one of a different type were not
prevented to do so, even if it was obvious, and stated in the doc,
that bad things would result from doing that.

To avoid mistakes, it is better to just forbid that though.

If one object is replaced with one of a different type, the only way
to keep the history valid is to also replace all the other objects
that point to the replaced object.

Isn't this a recursion problem? Taken in that order one unravels the
whole DAG.

However if considered in the reverse direction, one can replace an
existing object within the DAG with a carefully crafted alternative 
of
the same type, but which then wrongly references other dangling
objects which are then replaced by objects which have the right type
(this last replacement requires -f force).

I am not sure I understand what you are saying.

Anyway in a previous version of this patch I tried to be more explicit
about this, but Junio basically said that he found no value in
discussing this more explicitely...

I would agree that it's not worth discussing it more explicitly.

My comment was more about the direction of the line of reasoning which I 
felt was a bit Catch 22 when starting from an existing complete DAG (no 
garbage) and attempting to replace an object with another of a different 
type and still have a valid DAG.  The construction of the replacement 
items needs to be in the right order if one of the replacements is of 
the 'wrong' type (such a construction requires the creation or uses, and 
ultimately replacement of, extraneous objects that aren't (yet) in the 
DAG).

But as already been said that's a problem for the user of the --force 
option ;-)

Philip

Thanks,
Christian.