Subject: Re: BUG in git diff-index

From: Andy Lowry <[email-masked]>
Date: Thu, 31 Mar 2016 15:30:48 -0400

OK, great. I think the update-index command is what I need.

If you'll indulge me, I'll describe my use-case in detail, and if you 
see anything screwy about it, I'd appreciate feedback. But don't feel 
obligated - you've been a great help already.

This is all about publishing updates to a static web site hosted as a 
gh-pages branch on a github repo.

Our master branch has everything that goes into building the site, and 
we use subtree push to update gh-pages with the embedded subtree that 
contains the generated site.

I'm creating a bash script that does the publishing, and as a general 
rule, we want to publish only from the master branch, and only if it's 
clean and up-to-date. And we also want to make sure that the embedded 
site reflects the current source content.

It's in that last requirement where diff-index comes in. The script runs 
a site build, and then should fail the policy check if that results in 
any changes to the working tree (including the embedded site)/. /I don't 
want the script to change the index in any way (e.g. so that unintended 
changes revealed by this policy check are less likely to be accidentally 
commited).

If I understand correctly, the update-index operation you indicated will 
not change index membership at all, but will simply resync the index 
members with actual working tree files.

So I think now that the script should do "update-index --refresh" 
followed by "diff-index --quiet HEAD". Sound correct?

Andy

On 3/31/2016 10:27 AM, Jeff King wrote:
> On Thu, Mar 31, 2016 at 10:12:07AM -0400, Andy Lowry wrote:
>
>> What I'm actually after is a tree-to-filesystem comparison, regardless
>> of index. I've currently got a "diff" thrown in as a "work-around"
>> before "diff-index", but  now I understand it's not a workaround at
>> all. If there's a better way to achieve what I'm after, I'd appreciate
>> a tip. Otherwise I'll just change the comments explaining why there's
>> a "diff" in my script.
> If your workaround is just to refresh the index, then you can do "git
> update-index --refresh", rather than diff.
>
> I don't think there is a plumbing command to do a direct
> filesystem-to-tree comparison without having an index at all. "git diff
> <treeish>" claims in the documentation to do so, but besides not being
> plumbing, I think it is really just doing the same thing as diff-index,
> under the hood. The index is a pretty fundamental part of git's view of
> the working tree.
>
> -Peff