How to find a backwards merge in git?

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by johann , in category: General Help , 6 months ago

How to find a backwards merge in git?

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2 answers

by bobbie.kris , 6 months ago

@johann 

There is no native "backwards merge" concept in git, as merge commits are inherently forward-moving in the commit history. However, you can find reverse-merging situations or examine the changes introduced by a merge commit in the reverse direction.


To identify reverse-merging situations, you can use the following steps:

  1. Identify the commit where you suspect a reverse-merge has occurred. Let's call it reverse_merge_commit.
  2. Use the following command to view the commit's parents:
1
git show --summary reverse_merge_commit


  1. If the commit has multiple parents (more than one line displayed after Merge:


To examine the changes introduced by a merge commit in the reverse direction, follow these steps:

  1. Identify the commit you want to examine. Let's call it merge_commit.
  2. Use the following command to view the changes introduced by the merge commit:
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git show -m --first-parent merge_commit


This command displays a combined diff showing the changes introduced by the merge commit going in the reverse direction. The --first-parent flag ensures that only the changes from the first parent commit are shown, effectively ignoring any changes made in the merged branch.


Note that while these steps help you identify possible reverse-merge situations or examine changes in the reverse direction, they do not reverse the merge commit itself.

Member

by adelia , 2 months ago

@johann 

As mentioned, there is no direct "backwards merge" concept in git, and merges typically involve combining changes from a source branch into a target branch. However, if by "backwards merge" you mean investigating the changes introduced in a specific merge commit in the opposite direction (i.e., looking at the changes that were merged into the source branch), you can use the following steps:

  1. Identify the merge commit you want to examine. Let's call it merge_commit_hash.
  2. Use the following command to view the changes introduced by the merge commit in the reverse direction:
1
git show -m -c --reverse merge_commit_hash


Explanation of the command flags used:

  • -m or --patch-with-raw: Generate patch output with raw format.
  • -c or --cc: Combined diff format showing all changes from the merge.
  • --reverse: Output the diff in the reverse order, i.e., show the changes merged into the source branch.


By executing this command, you will see the changes that were merged into the source branch as a result of the merge_commit_hash. This can help you understand the alterations brought in by the merged branch without actually reversing the merge commit itself.


Remember that this command provides a detailed view of the changes, and you can analyze the differences line by line to comprehend the modifications introduced through the merge in the opposite direction.