Documentation : how to "undo" hg up

[Adrian Buehlmann]

On 17.09.2008 23:30, Peter Hosey wrote:
> On Sep 17, 2008, at 14:05:22, Patrick Waugh wrote:
>> Can someone explain what [hg up null] does, perhaps with an example?
> 
> Your working copy is relative to a specific version—a specific moment  
> in time.
> 
> `hg status` and `hg diff`, with no options, compare to the current  
> version of the working copy.
> 
> `hg up` is hg's time-travel command. It does two things:
> 
> 1. Changes the version that your working copy is relative to
> 2a. Merges changes between the former current version (before you ran  
> hg up) and the new current version (the version you're updating to)  
> into your local files.
> 2b (with -C). Replaces all your local files with the tree as of the  
> new current version.
> 
> Normally, the current version is a real version in the timeline. If  
> you run `hg log`, you'll see that version somewhere.
> 
> But in a repository that has never been updated (i.e., one that has no  
> working copy), the current version is null. The null version contains  
> no files, is not authored by anyone, and has no commit message.
> 
> If you run `hg init`, the resulting repository's current version is  
> null. You can push or pull to this repository, and it will have  
> changes, but unless you update, the current version doesn't change.  
> (Think of the “run hg update to get a working copy” message.)
> 
> So what hg up null does is travel back in time to before there were  
> any changes, before there were any files, before anyone had ever  
> touched the repository. The change that this makes to your working  
> copy is to remove it. You're left with only a repository.
> 
> The main reason to do this is if you're hosting a repository on a  
> server. You're probably not going to actually work with the files in  
> that repository—you'll work with another repository locally, and push  
> changes to and pull changes from the server's repository. Therefore,  
> the server's repo doesn't need a working copy.
> 
> So, if you update the server's repository (whether by accident, or by  
> not knowing any better, or because you wanted to check something), you  
> may later want to un-update it to conserve disk space.
> 
> That's what hg up null does.

I've added this to
http://www.selenic.com/mercurial/wiki/index.cgi/Update

Thanks!