How to git show a merge commit with combined diff output even when every changed file agrees with one of the parents

Question

After doing a  simple  merge  one without conflicts   git show usually only shows something like  commit 0e1329e551a5700614a2a34d8101e92fd9f2cad6  HEAD  master  Merge  fc17405 ee2de56 Author  Tilman Vogel  lt email email gt  Date    Tue Feb 22 00 27 17 2011  0100  Merge branch  testing  into master   This is because  for merges  git show uses the combined diff format which omits files that agree with either of the parent versions   Is there a way to force git to still show all differences in combined diff mode    Doing git show -m will show the differences  using pairwise diffs between the new and all parent versions respectively  but I would prefer to have that with the differnces marked by   - in the respective columns like in combined mode

User · Answer

I built a general-purpose approach to doing various operations on a merge's commits.

Step One: Add an alias to git by editing ~/.gitconfig:

[alias]
  range = "!. ~/.githelpers && run_on_merge_range"

Step Two: In ~/.githelpers, define a bash function:

run_on_merge_range() {
  cmd=$1; shift
  commit=$1; shift
  range=$(git show $commit | grep Merge: | awk '{print $2 "..." $3}')
  echo "git $cmd $range $@"
  if [ -z $range ]; then
    echo "No merge detected"
    exit 1
  fi
  git $cmd $range $@
}

Step Three: Profit!

git range log <merge SHA> --oneline
git range diff <merge SHA> --reverse -p
git range diff <merge SHA> --name-only

There is probably a LOT of room for improvement here, I just whipped this together to get past an annoying situation. Feel free to mock my bash syntax and/or logic.

User · Answer

You can use the diff-tree command with the -c flag  This command shows you what files have changed in the merge commit   git diff-tree -c  merged commit sha    I got the -c flag s description from Git-Scm      This flag changes the way a merge commit is displayed  which means it   is useful only when the command is given one   or --stdin     It shows the differences from each of the parents to the merge result   simultaneously instead of showing pairwise diff between a parent and   the result one at a time  which is what the -m option does     Furthermore  it lists only files which were modified from all parents

User · Answer

I think you just need  git show -c  ref   Trying this on the git repository on a8e4a59 shows a combined diff  plus minus chars in one of 2 columns   As the git-show manual mentions  it pretty much delegates to  git diff-tree  so those options look useful

User · Answer

Look at the commit message   commit 0e1329e551a5700614a2a34d8101e92fd9f2cad6  HEAD  master  Merge  fc17405 ee2de56 Author  Tilman Vogel  lt email email gt  Date    Tue Feb 22 00 27 17 2011  0100  Merge branch  testing  into master   notice the line   Merge  fc17405 ee2de56   take those two commit ids and reverse them  so in order get the diff that you want  you would do   git diff ee2de56  fc17405   to show just the names of the changed files   git diff --name-only ee2de56  fc17405   and to extract them  you can add this to your gitconfig   exportfiles    sh -c  git diff  0 --name-only    while read files  do mkdir -p    1   dirname  files     cp -vf  files  1   dirname  files   done     then use it by doing   git exportfiles ee2de56  fc17405  c temp myproject

User · Answer

A better solution  mentioned by  KrisNuttycombe    git diff fc17405   ee2de56   for the merge commit   commit 0e1329e551a5700614a2a34d8101e92fd9f2cad6  HEAD  master  Merge  fc17405 ee2de56 Author  Tilman Vogel  lt email email gt  Date    Tue Feb 22 00 27 17 2011  0100   to show all of the changes on ee2de56 that are reachable from commits on fc17405  Note the order of the commit hashes - it s the same as shown in the merge info  Merge  fc17405 ee2de56  Also note the 3 dots     instead of two   For a list of changed files  you can use   git diff fc17405   ee2de56 --name-only

User · Answer

If your merge commit is commit 0e1329e5  as above  you can get the diff that was contained in this merge by   git diff 0e1329e5   0e1329e5   I hope this helps

User · Answer

No  there is no way to do this with git show   But it would certainly be nice sometimes  and it would probably be relatively easy to implement in the git source code  after all  you just have to tell it to not trim out what it thinks is extraneous output   so the patch to do so would probably be accepted by the git maintainers   Be careful what you wish for  though  merging a branch with a one-line change that was forked three months ago will still have a huge diff versus the mainline  and so such a full diff would be almost completely unhelpful   That s why git doesn t show it

User · Answer

in your case you just need to  git diff HEAD  HEAD 2   or just hash for you commit   git diff 0e1329e55  0e1329e55 2

User · Answer

If you are sitting at the merge commit then this shows the diffs   git diff HEAD 1  HEAD  If you re not at the merge commit then just replace HEAD with the merge commit  This method seems like the simplest and most intuitive

User · Answer

Seems like answered here  https   public-inbox org git 7vd392ezhx fsf alter siamese dyndns org   So in a similar way  running   git diff --cc  M  M 1  M 2   git merge-base  M 1  M 2  should show a combined patch that explains the state at  M relative to the states recorded in its parents and the merge base

User · Answer

You can create branch with HEAD set to one commit before merge  Then  you can do   git merge --squash testing   This will merge  but not commit  Then   git diff

[git] How to "git show" a merge commit with combined diff output even when every changed file agrees with one of the parents?

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