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gitgit-subtree

git-subtree without squash: view log

I merged a tree onto a my repository by using git subtree add without the squash option. A git log shows that the commits were successfully added to the repository. However, if I do a git log --follow filename, the history stops at the merge and does not show previous commits. I tried using -M instead of --follow and that doesn't work either. How can I get a log of the commits for a specific file or files from before the merge?

Solution

  • Actually, git log --follow should work with subtree merges, but it is known to be hackish for a long time [1-3].

    One can stick with subtree merges and rest asured that the strategy is valid for tracking multiple histories, and patiently wait for the unavoidable event that git log --follow will improve. This may actually be a viable decision, since at present git log --follow can see some history in very useful cases. Say you moved a file from the toplevel repo to a sub-repo, then it can track the full move. When you want to track the history that is specific to a sub-repo, you really have to have a separate copy or check out a sub-repo branch.

    Alternatives and Workarounds

    You can get logs for the files like this [1]:

    git log -- '*filename'          # from the toplevel

    This views each commit that touched a file whose name ends with filename. It won't follow actual renames, and may show false positive if you have several files with the same basename [1].

    You can also merge the repositories using different strategies. Ref [4] shows a way to do this which is very close to what you have with regular subtree merging, but with traceable histories. Basically, you:

    1. add, fetch and merge each sub-repository to the toplevel repository as a regular remote, no git subtree or readtree. At first, this will polute your root dir as if it was theirs, so this is to be done at the beginning of a project's life.
    2. git mv the sub-repo files to separate folders

    Then:

    • upstream changes can be fetched and merged normally, but with the -Xsubtree flag to git merge.
    • other cases should be similar. I've tested pushing upstream and it works, see comment in [4].

    References

    [1] From the git mailing list http://git.661346.n2.nabble.com/Bug-Files-are-losing-history-after-subtree-merge-td7597197.html

    [2] From the git mailing list http://git.661346.n2.nabble.com/gsoc-Better-git-log-follow-support-td6188083.html#a6188352

    [3] git log --follow has been in Google Summer of Code https://git.wiki.kernel.org/index.php/SoC2011Ideas#Better_git_log_--follow_support

    [4] https://saintgimp.org/2013/01/22/merging-two-git-repositories-into-one-repository-without-losing-file-history