Why Ankh isn’t an SCC provider

A question that comes up occasionally is why AnkhSVN wasn’t implemented using the Microsoft Source Code Control Interface (MSSCCI). This is a de-facto standard today for integrating source control into various IDEs and other application, so it would seem like a natural choice for integrating Subversion into the Visual Studio IDE. However, we chose to take another approach and implement AnkhSVN as a regular Visual Studio addin instead.

Initial planning on AnkhSVN started in December of 2002. At that time, it was a school project that was supposed to last throughout the spring semester of 2003 at Oslo University College. I had some clear ideas about what I wanted to do for my project: I wanted to make something open source, I wanted to relate it somehow to Subversion and I wanted to implement it using C#/.NET, since those were my interests at the time (and still are). Using MSSCCI conflicted with goals #1 and #3. In 2002, the MSSCCI API was under a strict Non-Disclosure Agreement, meaning we wouldn’t have been able to make something open source if we were to use it. There was also a rumor going around that getting hold of the right person inside Microsoft in order to obtain the documentation for the API and sign the NDA was something of a Kafkaesque quest. Since we didn’t attempt to go down this route, I never did find out whether this was true.

Another problem with MSSCCI is that it is essentially a specification for a number of exported C functions from a DLL. At that time I had dabbled with C#/.NET for a while and wanted to try it out for a major project. A .NET assembly cannot (easily, there are ways…) export regular functions, so implementing an MSSCCI provider using .NET would prove to be rather awkward. The technical problems here aren’t insurmountable, however, I can easily think of some ways in which we could have made Ankh using MSSCCI and still got to write most parts of it in .NET. If there hadn’t been other reasons for not using MSSCCI, this problem alone wouldn’t have caused us to make the choice we did. If MSSCCI had been the best choice, it’s also quite possible that we would have implemented the whole thing in C++ instead.

MSSCCI, unfortunately, has one more major problem: it’s not a very good API. It is more or less designed around the needs of Visual Sourcesafe, and source control systems that don’t subscribe to the same ideology as VSS plain don’t fit very well into it. Eric Sink (founder of Sourcegear, which makes the Vault source control system) , in his excellent series Source Control HOWTO, writes about MSSCCI’s deficiencies in Chapter 9: Source Control Integration with IDEs. Which is good, because then I don’t have to go on about it here.

We already knew about most of the criticisms leveraged at MSSCCI back when we were planning the project, so it proved to be the final and decisive argument against using it for Ankh.