Re: diff-files inconsistency with touched files

[James Spencer <jss43@cam.ac.uk>]

Jeff King wrote:
> On Wed, Sep 02, 2009 at 06:27:15PM +0100, James Spencer wrote:
> 
>> $ git diff-files
>> $ touch test
>> $ git diff-files
>> :100644 100644 9daeafb9864cf43055ae93beb0afd6c7d144bfa4
>> 0000000000000000000000000000000000000000 M  test
>> $ git diff
>> $ git diff-files
>> $
>>
>> I don't understand why git diff-files reports a file is changed when
>> that file is touched nor why running git diff changes this to (what I
>> think is) the correct behaviour.
> 
> Git uses the stat information of a file to know whether what we have
> cached in the index is up-to-date or not. So in the first diff-files, we
> don't even have to look at the contents of "test"; we see that it hasn't
> changed since the last time we looked at the contents, and that its
> sha-1 matches what's in the index, so there is no diff.
> 
> By running "touch", you have changed the stat information, so we believe
> there may be a difference. But we don't actually know what's _in_ the
> new side, so we just print the null sha1 instead of the actual sha1
> contents.
> 
> Diff-files _could_ refresh the cache each time it runs, but we
> intentionally do not do that. Doing so is a little bit expensive, and
> because diff-files is intended as a low-level tool for scripts, we give
> the script the flexibility (and responsibility) of refreshing the cache
> when it wants to. So you could do:
> 
>   $ git update-index --refresh
>   $ git diff-files
> 
> and get clean output.
> 
> You see different behavior from "git diff" because it is meant for user
> consumption and therefore refreshes the cache automatically at the
> beginning of every run.
> 
> -Peff

Thanks for your help!

    --James