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Comment by pmoriarty | Hacker News Reader

"Git has no first-class concept of file name changes. Instead it tries to use heuristics to spot renames and sometimes they work and sometimes they won't."

Git has the "mv" command. If you "git mv" a file, why would git have to guess or use heuristics to figure out that the file was renamed?

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As the Git FAQ [0] says:

> Git has a rename command git mv, but that is just for convenience. The effect is indistinguishable from removing the file and adding another with different name and the same content.

git diff, merge, and related tools have heuristics for detecting file moves (off by default, turned on with e.g. git diff -M) but they tend to break if a file is both moved and modified in the same commit.

[0] https://git.wiki.kernel.org/index.php/GitFaq#Why_does_Git_no...

Yeah exactly why I always commit renames right away and atomically. I mean it's a _relatively_ rare thing and when I have to do it I just want to make and record the change and then move on. Renaming and then modifying a file in the same commit is slightly sloppy imo. Not to say that the tool couldn't be doing a better job.

Because git stores sets of files. If you move a file and make a new commit, it's just a new set of files which says "this old set is my parent". There is nothing in there about the renamed file.

Still, at the point you do a "git mv", it can't be said that git doesn't know you renamed a file. It knows.

In fact, after a "git mv foo bar", if you do a "git status", you'll see:

  On branch master
  Changes to be committed:
    (use "git reset HEAD <file>..." to unstage)
  
          renamed:    foo -> bar

If git chooses afterwards to discard that information and do nothing with that knowledge, that's a separate problem.

I don't know enough about Git internals in this regard, but it's possible that in fact the index is just being compared to HEAD to infer that information. Index has a file called "bar" and none called "foo". HEAD is vice versa.

Yes, Git has "mv". Git also detect file rename. I'm not aware of the method though. I'm talking based on experience. I renamed some file normally, without Git. When I checked the `git status`, Git says it was renamed.

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