Git "missing" commit

Question

I'm in a situation where some changes made in a feature branch are not reflected in master, even though this branch was merged into it. I'm at a loss to understand why. For simplicity, let's say this commit has a hash "A" and changed file "file"

This can probably best be illustrated by the following commands:

$ git checkout master

$ git branch --contains A
* master
feature_branch

$ git log file | grep A
(no output)

$ git checkout feature_branch

$ git log file | grep A
A

Can anyone explain what's going on here? More importantly, is there anything that can be done to prevent this in the future?

EDIT:

As mentioned by a few people, the following does show the commit:

$ git checkout master

$ git log --follow file | grep A
A

But the thing is... the file was not renamed. So that doesn't fully explain things, either..

Answer 1

You are a victim of an evil merge.

Here is how to reproduce it

git init testrepo
cd testrepo

touch initial
git add initial
git commit -m 'initial commit'

git checkout -b feature_branch
echo "A" >> file
git add file
git commit -m 'file committed'

git checkout master

Now do an interactive merge as if there were merge conflicts

git merge --no-commit --no-ff feature_branch

and move the file file (evil merge).

testrepo (master|MERGING)

git mv file someOtherFile
git commit

Now you will see that branch master contains the commit (in my case 9469682) that introduced file file

 git branch --contains 9469682
  feature_branch
 * master

But a git log will not show it, because it was moved

 git log -- file
 (no output)

Use

git log --follow -- file

and the commit appears again.

Also keep in mind that the merge can get more evil. If the file's content also changed a lot than èven git log --follow will not detect it, because of the rename threshold.

In this case use git log --follow --find-renames= to adjust the rename threshold.

If generating diffs, detect and report renames for each commit. For following files across renames while traversing history, see --follow. If n is specified, it is a threshold on the similarity index (i.e. amount of addition/deletions compared to the file’s size). For example, -M90% means Git should consider a delete/add pair to be a rename if more than 90% of the file hasn’t changed. Without a % sign, the number is to be read as a fraction, with a decimal point before it. I.e., -M5 becomes 0.5, and is thus the same as -M50%. Similarly, -M05 is the same as -M5%. To limit detection to exact renames, use -M100%. The default similarity index is 50%.