Finding all commits which modify a file

Hello,

I'm trying to find /all/ commits that change a file in the repository...and its proving to be trickier than I thought. :-)

The situation that we were dealing with is this:

- Person A and person B both pull from the same central repository.

- Person A makes a change to file foo.txt and bar.txt, commits, and pushes
to the central repository.

- Person B makes a similar change to bar.txt and commits it.

- Person B does a fetch and merge.  Since both A and B made changes to
bar.txt, this requires conflicts to be resolved manually.

- B reverts A's changes to foo.txt. (If B is coming from a different
revision control system, this may happen due to confusion about how merges
are handled.)

- B commits the changes.

- B makes more changes to bar.txt, commits them, and pushes to the central
repository.

At this point, A's changes to foo.txt have been undone.

Graphically:

    A1
   /  ^
  v    \
  C1   B2<-B3
  ^    /
   \  v
    B1

B1, B2, and B3 have the same version of foo.txt as C1, A1 modifies it.

Person A discovers that his changes are missing and wants to know what happened.

git log foo.txt doesn't help; it won't even show commit A1, due to history simplification.

git log --full-history foo.txt will show commit A1. It still won't show commit B2, though, which we'd also like to show (because that's where the change to foo.txt got removed).

I would think that git log --simplify-merges foo.txt would have done what I'd wanted, but it still does not show commit B2. Based on what I'm reading in the man page, I would expect the simplification to go like this:

    A1
    | ^
    |  \
    |  B2<-B3
    |  /
    v v
    C1

(since B1 is TREESAME as C1 if we're only considering foo.txt)

    A1
    | ^
    |  \
    |  B2<-B3
    |
    v
    C1

(since C1 is an ancestor of A1)

However, the actual output only includes A1, not B2.

 - Can someone explain this, and/or
 - can someone offer a command to display all commits (including merges)
in which ANY parent is not TREESAME?

Thanks!

- Neal