Re: 'git log' doesn't keep log of un-removed and then renamed directory

From: Chris Torek <chris.torek@gmail.com>
Date: Aug 14, 2021, 10:18 UTC
Message-ID: <CAPx1Gvdb=rtjWmc1Qe5iZyuwSF+s-YO7G__VUZ=iZw3x4bAKCw@mail.gmail.com>
In-Reply-To: <75911f47-1433-f0a4-7d46-f1fb2fd44cf4@rawbw.com>

On Sat, Aug 14, 2021 at 2:21 AM Yuri <yuri@freebsd.org> wrote:

Show 5 quoted lines

>
> In the FreeBSD ports tree I restored the previously removed directory
> math/dynare:
>
> 1. git checkout 3fb72e318f7be~1 -- math/dynare

[remaining complex shuffling action that mimics what's needed in SVN, snipped]

Git is not SVN; do not expect it to behave *like* SVN.

In particular, Git does not have file history.  Git has only commits.

SVN has commits, but SVN commits contain file history. In Git, the commits *are* the history, and are the *only history*. Each commit has a full snapshot of every file, under the names you told Git to use, with the contents that you told Git to save.

The command `git log science/dynare` tells Git: Look through commits, one by one, and whenever there's a file whose name starts with `science/dynare` that's different in *this* commit, vs the previous one, tell me about this commit. Since the old commits have files named `math/dynare/something` instead, Git doesn't tell you about them.

The `git log` command has a flag, `--follow`, that has a trick up its sleeve (wait: does `git log` have sleeves? well, anyway). This trick is a bit limited though. Let's say there's a README file in the science/dynare/ directory, as of the latest commit. If you run:

    git log --follow science/dynare/README

Git will look at *this* commit and find the file, and will look at this commit's *parent* and *not* find the file, because the parent does not have `science/dynare/README` in it. But the parent does have `math/dynare/README` in it *and that file exactly matches* this commit's copy. So `git log` will tell you about this commit and say that the file was *renamed*. From this point backwards, `git log` will be looking, not for `science/dynare/README`, but instead for `math/dynare/README`.

Unfortunately, the `--follow` trick only works on *one file*. But it will let you know that if you re-run your `git log` with `math/dynare` you can see what happened before the renaming.

A future `git log` really should be smarter about detecting the whole-subtree renaming, and be able to follow it. This won't require any change in the repository, just a smarter `git log`. But someone has to write that smarter `git log`.

Chris