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# A few bits about the RCS backends

## Terminology

``web-edit'' means that a page is edited by using the web (CGI) interface
as opposed to using a editor and the RCS interface.


## [[Subversion]]

Subversion was the first RCS to be supported by ikiwiki.

### How does it work internally?

Master repository M.

RCS commits from the outside are installed into M.

There is a working copy of M (a checkout of M): W.

HTML is generated from W.  rcs_update() will update from M to W.

CGI operates on W.  rcs_commit() will commit from W to M.

For all the gory details of how ikiwiki handles this behind the scenes,
see [[commit-internals]].

You browse and web-edit the wiki on W.


## [darcs](http://darcs.net/) (not yet included)

Support for using darcs as a backend is being worked on by [Thomas
Schwinge](mailto:tschwinge@gnu.org).

### How will it work internally?

``Master'' repository R1.

RCS commits from the outside are installed into R1.

HTML is generated from R1.  HTML is automatically generated (by using a
``post-hook'') each time a new change is installed into R1.  It follows
that rcs_update() is not needed.

There is a working copy of R1: R2.

CGI operates on R2.  rcs_commit() will push from R2 to R1.

You browse the wiki on R1 and web-edit it on R2.  This means for example
that R2 needs to be updated from R1 if you are going to web-edit a page,
as the user otherwise might be irritated otherwise...

How do changes get from R1 to R2?  Currently only internally in
rcs\_commit().  Is rcs\_prepedit() suitable?

It follows that the HTML rendering and the CGI handling can be completely
separated parts in ikiwiki.

What repository should [[RecentChanges]] and [[History]] work on?  R1?

#### Rationale for doing it differently than in the Subversion case

darcs is a distributed RCS, which means that every checkout of a
repository is equal to the repository it was checked-out from.  There is
no forced hierarchy.

R1 is nevertheless called the master repository.  It's used for
collecting all the changes and publishing them: on the one hand via the
rendered HTML and on the other via the standard darcs RCS interface.

R2, the repository the CGI operates on, is just a checkout of R1 and
doesn't really differ from the other checkouts that people will branch
off from R1.

(To be continued.)


## [[Git]]

Regarding the Git support, Recai says:

I have been testing it for the past few days and it seems satisfactory.  I
haven't observed any race condition regarding the concurrent blog commits
and it handles merge conflicts gracefully as far as I can see.

As you may notice from the patch size, GIT support is not so trivial to
implement (for me, at least).  Being a fairly fresh code base it has some
bugs.  It also has some drawbacks (especially wrt merge which was the hard
part).  GIT doesn't have a similar functionality like 'svn merge -rOLD:NEW
FILE' (please see the relevant comment in mergepast for more details), so I
had to invent an ugly hack just for the purpose.