git-mv redux: there must be something else going on

Based on my current understanding of git there should be no difference between a git mv and a git rm followed by a git add. But empirically there is a difference. git log --M --follow is able to track files through git mvs even if their content changes completely. Likewise, it does *not* track files through rm/add combinations even if the content didn't change at all. (See experiment transcript below.)

So something in my understanding of how git works must be wrong. Git must be keeping a separate record of file renames somewhere. But where?

Just for the record, I'm not complaining about this behavior. In fact, what git does is exactly what I want. I just want to understand how it works.

Thanks, rg

---

[ron@mickey:~/devel/gittest]$ cat>file1
1
2
3
4
5
[ron@mickey:~/devel/gittest]$ cat>file2
a
b
c
d
e
[ron@mickey:~/devel/gittest]$ git init
Initialized empty Git repository in /Users/ron/devel/gittest/.git/
[ron@mickey:~/devel/gittest]$ git add file1
[ron@mickey:~/devel/gittest]$ git commit -m 'Add numbers'
[master (root-commit) 54c2e4a] Add numbers
 1 files changed, 5 insertions(+), 0 deletions(-)
 create mode 100644 file1
[ron@mickey:~/devel/gittest]$ git rm file1
rm 'file1'
[ron@mickey:~/devel/gittest]$ git add file2
[ron@mickey:~/devel/gittest]$ git commit -m 'numbers->letters'
[master fe05d12] numbers->letters
 2 files changed, 5 insertions(+), 5 deletions(-)
 delete mode 100644 file1
 create mode 100644 file2
[ron@mickey:~/devel/gittest]$ git log --name-status -M --follow file2
commit fe05d1233be1bb11f4ed0e8496e4191795d515a0
Author: rongarret <ron@mickey>
Date:   Wed Feb 3 10:13:38 2010 -0800

   numbers->letters

A       file2
[ron@mickey:~/devel/gittest]$ ls
file2 git/
[ron@mickey:~/devel/gittest]$ cat>file2
6
7
8
9
10
[ron@mickey:~/devel/gittest]$ git mv file2 file3
[ron@mickey:~/devel/gittest]$ git commit -m 'letters->numbers'
[master ae3f6d4] letters->numbers
 1 files changed, 0 insertions(+), 0 deletions(-)
 rename file2 => file3 (100%)
[ron@mickey:~/devel/gittest]$ git log --name-status -M --follow file3
commit ae3f6d440483fa41cf08819237e87d567ac3a31d
Author: rongarret <ron@mickey>
Date:   Wed Feb 3 10:15:00 2010 -0800

    letters->numbers

R100    file2   file3

commit fe05d1233be1bb11f4ed0e8496e4191795d515a0
Author: rongarret <ron@mickey>
Date:   Wed Feb 3 10:13:38 2010 -0800

   numbers->letters

A       file2
[ron@mickey:~/devel/gittest]$ ls
file3 git/
[ron@mickey:~/devel/gittest]$ mv file3 file4
[ron@mickey:~/devel/gittest]$ git rm file3
rm 'file3'
[ron@mickey:~/devel/gittest]$ git add file4
[ron@mickey:~/devel/gittest]$ git commit -m 'rm/add identical content'
[master a3d7227] rm/add identical content
 2 files changed, 5 insertions(+), 5 deletions(-)
 delete mode 100644 file3
 create mode 100644 file4
[ron@mickey:~/devel/gittest]$ git log --name-status -M --follow file4
commit a3d7227fc2edca75fff8894acd5b077d1788bb36
Author: rongarret <ron@mickey>
Date:   Wed Feb 3 10:17:23 2010 -0800

    rm/add identical content

A file4 [ron@mickey:~/devel/gittest]$