impure renames / history tracking

Hi,

I'm trying to understand git better (so I can explain it better to 
others, with an eye to them considering switching to git), one 
question I have is about renames.

- git obviously detects pure renames perfectly well

- git doesn't however record renames, so 'impure' renames may not be
   detected

My question is:

- why not record rename information explicitely in the commit object?

I.e. so as to be able to follow history information through 'impure' 
renames without having to resort to heuristics.

E.g. imagine a project where development typically occurs through:

o: commit
m: merge

    o---o-m--o-o-o--o----m <- project
   /     /              /
o-o-o-o-o--o-o-o--o-o-o <- main branch

The project merge back to main in one 'big' combined merge 
(collapsing all of the commits on 'project' into one commit). This 
leads to 'impure renames' being not uncommon. The desired end-result 
of merging back to 'main' being to rebase 'project' as one commit 
against 'main', and merge that single commit back, a la:

    o---o-m--o-o-o--o----m <- project
   /     /              /
o-o-o-o-o--o-o-o--o-o-o---m <- main branch
                        \ /
                         o <- project_collapsed

So that 'm' on 'main' is that one commit[1].

The merits or demerits of such merging practice aside, what reason 
would there be /against/ recording explicit rename information in the 
commit object, so as to help browsers follow history (particularly 
impure renames) better in a commit?

I.e. would there be resistance to adding meta-info rename headers 
commit objects, and having diffcore and other tools to use those 
headers to /augment/ their existing heuristics in detecting renames?

Thanks!

1. Git currently doesn't have 'porcelain' to do this, presumably 
there'd be no objection to one?

regards,
-- 
Paul Jakma	paul@clubi.ie	paul@jakma.org	Key ID: 64A2FF6A
Fortune:
It is the quality rather than the quantity that matters.
- Lucius Annaeus Seneca (4 B.C. - A.D. 65)