Taras has recently upload a patch to bmo to remove outparam in QI. After 
I pulled his repos from hg.mozilla.org, I was not even able to run 
'./configure'.

I was using a latest Mercurial 0.9.4, when I reverted to 0.9.1 
everything worked fine. Upon investigation, I found that Taras used hg 
merging in those repos.

Contrary to hg advertising, hg revision turns out *NOT* to be immutable. 
Different versions of hg treat the same of ChangeSets differently.

This is an inherent flow rooting in delta model. With n ChangeSets and m 
algorithms to apply them, there is m^n variants (^ means power). It is 
perfectly fine as long as there is only *one* algorithm. But when merges 
come in, things really become complicated.

Of course, there is a easy solution: to store intermediate states. And 
this is exactly how *git* works. Except from this stability, git may 
bring additional benefits to Mozilla. I would quote Linus Torvalds here 
from http://www.gelato.unsw.edu.au/archives/git/0505/2784.html

> Note that we discussed this early on, and the issues with full-file 
> handling haven't changed. It does actually have real functional 
> advantages:
> 
>  - you can share the objects freely between different trees, never 
>    worrying about one tree corrupting another trees object by mistake.
>  - you can drop old objects.
> 
> delta models very fundamentally don't support this. 

The first point in the list is the top priority that Brendan Eich 
mentioned for the mozilla2 SCM system in March 2007:

> [sic] we anticipate many experimental branches (for Tamarin work,
> Oink/Elsa-based refactoring, etc.) and related integration branches
> feeding back into the main Mozilla 2 branch. 

In fact, that is exactly the process, they develop linux kernel. Mozilla 
will only need an equivalent of '-mm' kernel branch to complete the picture.

As a disclaimer I add that I am not counter-mercurial. I have svn, hg 
and git repositories set up for my project to facilitate cooperation. 
But I do personally prefer git to manage my working tree since its 
stability gives me a feeling of protection.

--
Sergey Yanovich
- abstract ERP leader
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