Git: How to maintain two branches of a project and merge only shared data?

Question

Suppose I have two branches of a project IMClient-MacOS and IMClient-Windows, and their code only differs by (let's say) one directory main/. All the other directories contain system-independent code and are interchangeable.

Some workers work on the Windows version, and some work on the MacOS version. How do they prevent overwriting changing into the main/ directory when they merge from their counterparts' branch? Is there a way to merge in Git that will always ignore the OS-dependent directory?

Answer 1

There's an option for ignore the whole file or directory structure, but then those file won't get added to the repo at all. I think you already know that, by using .gitignore file

What I think is having a separate branch for Windows and OS X's code, as you said. Then you'll merge the change by cherry-picking the code from the other branch (the syntax is git cherry-pick refspec) However, those developers should always watch for a 'change' on other os's branch.

I would also suggest that always make a separate commit for files in main, so that it won't be mix-up when you're cherry-picking the branch.

Answer 2

An alternative to trying to filter merges would be to split the common and OS-specific parts into two repositories. You can then set up the one as a submodule for the other. Whether to have the common part set up as a submodule of the OS specific parts, or the other way around probably depends a bit on where do most of the commits go.

Answer 3

You can probably solve your problem with git, but your life will be vastly simpler if you put the system-dependent code in different directories and deal with the cross-platform dependencies in the build system (Makefiles or whatever you use). Or is there some good reason I've overlooked to have code from different systems share one directory?

Answer 4

Do not use just one branch per platform (windows and mac).

Instead, have at least three branches: Generic, windows and mac. The generic branch does not have any system dependent code, and a platform branch does not have any generic code, hence none of the branches will build by itself. Instead, a mac developer always creates a throw-away branch that is a merge between generic and mac in order to build.

Then, develop and commit generic features to generic branch, with associated platform support code on platform branches.

Even better would be to have a single codebase that will be buildable on both platforms by the build system (makefile variables and conditional compilation). Then a mac developer will add a generic feature and platform support code for the new feature only for mac while adding a non-working stub for other platforms, and hand the result to developers on other platforms to fill in the stubs.