Git changes modification time of files

In the GitFaq I can read, that

Git sets the current time as the timestamp on every file it modifies, but only those.

However, I tried this command sequence:

$ git init test && cd test
Initialized empty Git repository in d:/test/.git/

$ touch filea fileb

$ git add .

$ git commit -m "first commit"
[master (root-commit) fcaf171] first commit
 0 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 filea
 create mode 100644 fileb

$ ls -l > filea

$ touch fileb -t 200912301000

$ ls -l
total 1
-rw-r--r--    1 exxxxxxx Administ      132 Feb 12 18:36 filea
-rw-r--r--    1 exxxxxxx Administ        0 Dec 30 10:00 fileb

$ git status -a
warning: LF will be replaced by CRLF in filea
# On branch master
warning: LF will be replaced by CRLF in filea
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#






#       modified:   filea
#

$ git checkout .

$ ls -l
total 0
-rw-r--r--    1 exxxxxxx Administ        0 Feb 12 18:36 filea
-rw-r--r--    1 exxxxxxx Administ        0 Feb 12 18:36 fileb

Why did Git change the timestamp of file fileb? I'd expect the timestamp to be unchanged.

Are my commands causing a problem? Maybe it is possible to do something like a git checkout . --modified instead?

I am using git version 1.6.5.1.1367.gcd48 under MinGW and Windows XP.

Solution

This doesn't occur on a Linux filesystem. I tested the exact scenario you described and my modification times are preserved for the files I have left untouched:

sean@SEAN-PC:~/Desktop/test$ ls -la tests/BusTests.*
-r--r--r-- 1 sean sean 8 2010-02-11 11:53 tests/BusTests.c
-r--r--r-- 1 sean sean 1 2010-02-11 11:51 tests/BusTests.h

sean@SEAN-PC:~/Desktop/test$ git status -a
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       modified:   tests/BusTests.c
#

sean@SEAN-PC:~/Desktop/test$ git checkout .

sean@SEAN-PC:~/Desktop/test$ ls -la tests/BusTests.*
-r--r--r-- 1 sean sean 1 2010-02-11 11:55 tests/BusTests.c
-r--r--r-- 1 sean sean 1 2010-02-11 11:51 tests/BusTests.h

I suspect that this is an unknown bug in the MinGW build of Git. You might want to report it to the developers: http://code.google.com/p/msysgit/issues/list

It would be interesting to see if the BusTests.h modification stamp is modified when you only checkout the modified file:

git checkout -- tests/BusTests.c