Re: behaviour of git diff, GIT_DIR & checked out tree

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi,

On Mon, 24 Sep 2007, David Tweed wrote:

> In a git tracked tree rooted at $HOME/V with
> git-dir of $HOME/V/.git, if I'm in $HOME/V then
> 
> git diff master@{midnight}
> 
> tells me the difference between the current modified files
> in the tree being tracked in V and the specified commit. In
> a different directory, OUTSIDE of $HOME/V, I tried
> 
> env GIT_DIR=$HOME/V/.git git diff master@{midnight}
> 
> to get the same effect but, whilst I do get a diff output, it
> looks like a diff of the commit against an empty tree.

Yes, this is fully expected.

The @{time} notation accesses the _reflogs_, which are purely local 
beasts.  They are not transmitted when cloning.

The rationale: in a distributed environment, you cannot trust others' 
timestamps.  Therefore we don't.

We can only (to a certain extent, at least) trust our _own_ timestamp.  
That is why we have timestamp access to the reflogs (which are purely 
local, as I mentioned above), but we have no way to reference commits by 
timestamp otherwise.

Hth,
Dscho