How does git find subtree, when we use subree merging strategy?

Question

How does git find subtree, when we use subtree merging strategy? I find only one mention here: "It actually guesses the subtrees that you want to merge. Usually, this magically turns out to be correct, but if your subtree contains a lot of changes (or was originally empty, or whatever), then it can fail spectacularly." How does it guess and what can i do, if it fails? Is something changed since aug'09, when that answer were written?

Answer 1

Here are some helpful articles about subtree merging:

http://blog.brad.jones.name/2011/10/52/merging-two-git-repositories-history

http://kernel.org/pub/software/scm/git/docs/howto/using-merge-subtree.html

https://help.github.com/articles/working-with-subtree-merge

The state of subtree merges has changed since the date asked, including the addition of --Xsubtree= parameter to allow you to bypass the "guess".