svn script to rename member variables on checkout/update

Question

I work with a guy who prefers to name his member variables using the mCamelCase convention, for example: mSomeVar or mSomeOtherVar. I can't stand this format. I prefer the m_camelCase convetion, for example: m_someVar or m_someOtherVar. We drive each other mad looking at each other's code.

Now we've added a new guy to the team and he prefers no prefix at all. Since we use svn, we were thinking we could develop an svn script that renames member variables on the fly when you download the code form the server. This way everyone can get the member variables named whatever they want.

Does anyone have any example svn scripts that can do this sort of thing? I've seen scripts that change comment headers but we need something that includes a C++ processor.

Answer 1

Subversion doesn't have hooks that work on update - you could have a post-commit hook* that would allow you to convert from one convention to another (repository standard), and you could use a script that you write yourself that does the checkout, and then performs the necessary adjustments, but this would give you false readings on svn diff etc.

My suggestion is to just sit down with your colleagues and agree on a standard. The post-commit hook would still be useful to catch slip-ups though.

*I'm thinking something that sees a commit has occurred, automatically checks out and alters the code to adhere to the repository standard convention, and then commits if necessary. Another option is to have a pre-commit hook that disallows the commit if the code doesn't adhere to the standard.

Answer 2

Sounds like a recipe for disaster. In order to get this to work you'd need to decide on a repository wide standard, where every file uses the same variable naming conventions. If you can do that, why not just have everyone code like that?! The important thing about conventions is not which convention you use but that everyone actually uses the same convention!

Find someone with seniority to make the call (or pull rank, if you can), everyone else will just have to suck it up.

Answer 3

I'll assume you want to change the style for research purposes, and the question is simply hypothetical. Joel S. seems to think that answers which simply say your doing something wrong aren't good answers at all, so I'll try to attempt to give you some avenues to approach your problem.

The closest thing which svn does in terms of transforms is it can change the line ending on check-out, and change it again on check-in. This allows the repository to have a single idea of a line ending, and for different clients to have the files modified to their preferences. While this feature sounds fairly straight forward, a number of people seem to have problems getting it to work correctly. Simply Google 'svn eol-style'.

Since svn does not provide any sort of customizable client side filters, I think it would be safe to assume you are going to need to modify the svn client, and compile it for your own purposes. Perhaps you could submit a patch or an extension back to svn.

So at this point, you should have downloaded the svn source, and be able to get it to compile the client. At this point, turn your attention to libsvn_subr/subst.c. This file contains the routines to translate to and from various formats. Currently it does translation on keyword expansion and eol's.

You simply need to create a new property, maybe called member-variable-style. For files which have this flag set, you can invoke a special transform in the subst.c code. You could be able to track down reference in svn to the transform code by looking at the calls to svn_subst_translate_stream3.

OK. That was the easy part. Now you need to get a function to properly translate your code from one form to another. You can't simply pull out the cpp processor out of gcc, because there is no guarantee the code will be valid / compile. You have to do your best job creating lexing rules which hopefully will do the right thing on the right variables. For varaibles starting with m_ or even m, this is fairly straight forward to do. Unfortunately, for the member on your team who doesn't use m_ at all, it can be quite a challenge determining what it a member variable in C++. Fortunately, there exists quite a bit of research in the field done by people who create syntax highlighting code. I'd poke around and find some code which does a good job highlighting C++ code.

Lastly, as these transforms could become quite complicated, I'd suggest you have svn shell out to a filter program at this stage. This wouldn't be great for performance, but it would make it much easier to write and debug your filter. You could then write your filter in Perl or the language of your choice. For a good example of using external an external filter program, see Squid redirectors.

Good luck!