Sunday, 5 October 2008

Merge in SVN

At the end of the day there will be times in which branching will occur, resulting in the need to merge changes from one code line to another. Merging in an SVN system is a little different then what I expected resulting in me making Mistakes from time to time.

Merge in SVN is a ternary operation

I for one was used to treat merge as a binary operation. you take one source file and merge it into another resulting in the combined changes from them both. In SVN however, the merge operation always involves three factors. In fact I would think that a better name for merging in SVN would be “diff and apply”. When merging, we first take a given revision on a code line which we want to merge from compare it to some previous version on that line and apply the differences into a different code line that is the target of the merge operation.


1. lets say we have a trunk and a branch and we want to merge the last set of changes committed on the branch to the trunk.

The merge operation involves comparing the head revision of the branch to its previous revision (to extract the latest committed changes only) and then applying them to a local folder containing the head revision of the trunk.

2. Lets say we want to merge a complete branch back into the main trunk.

In the merge operation we take the head revision of the branch, compare it to the revision in which we branched from the main code line (this will give us all the changes made on the branch in relation to the main trunk) and apply the changes into a and then applying them to a local folder containing the head revision of the trunk.

Merge using TortoiseSVN

The good news are that the latest version of the TortoiseSVN client has greatly improved their merging GUI. The new TortoiseSVN now includes much simpler interface for doing common merge operation. (The new version also have a mechanism for tracking merge operation to avoid duplicate merges, but since I’ve not really used that I’m not sure how useful that is)


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