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Tag Old Commits

Sometimes, I forget to tag commits after pushing to the main branch. This script helps you backdate and tag old commits in Git after the fact, ensuring that your tags are correctly assigned even if they weren't created at the time of the original commit.

PowerShell Script

# Define the commit hash, tag version, and message
$ENV:TAG_HASH = "a90bea740b8e294b076f4308c973513f6a2c4ae9"
$ENV:TAG_VERSION = "0.0.8"
$ENV:TAG_MESSAGE = "Release $ENV:TAG_VERSION"

# Delete local and remote tags if they already exist
git tag -d "$ENV:TAG_VERSION"  # Delete the local tag
git push --delete origin "$ENV:TAG_VERSION"  # Delete the remote tag

# Switch to the commit that you want to tag (detached HEAD state)
git switch --detach $ENV:TAG_HASH

# Set the committer date to match the original commit date
$ENV:GIT_COMMITTER_DATE = git show --format=%aD | Select -First 1

# Create and sign the new tag on the specified commit
git tag -s $ENV:TAG_VERSION $ENV:TAG_HASH -m $ENV:TAG_MESSAGE

# Push the tag to the remote repository
git push origin "$ENV:TAG_VERSION"

# Clean up environment variables and return to the main branch
$ENV:GIT_COMMITTER_DATE = ""
$ENV:TAG_HASH = ""
$ENV:TAG_VERSION = ""
$ENV:TAG_MESSAGE = ""
git switch main

How It Works

This script automates the following process:

  1. Deletes any existing local and remote tags for the specified version.
  2. Switches to the commit where you want to place the tag.
  3. Sets the committer date to the date of the original commit (this ensures the tag appears on the correct commit date).
  4. Creates and signs the new tag on that commit.
  5. Pushes the tag to the remote repository.

Explanation of Key Steps

  1. Delete Existing Tags:
    The script first deletes any local and remote tags with the same version name to ensure that no conflicts occur when you create a new tag for the commit.

powershell git tag -d "$ENV:TAG_VERSION" git push --delete origin "$ENV:TAG_VERSION"

  1. Switch to the Commit:
    The script uses git switch --detach to enter a "detached HEAD" state at the specified commit hash. This allows you to operate on that commit without changing the current branch.

powershell git switch --detach $ENV:TAG_HASH

  1. Set the Committer Date:
    The committer date is set to match the date of the original commit. This is important to ensure that the tag appears as though it was created at the time of the original commit, rather than when you run the script.

powershell $ENV:GIT_COMMITTER_DATE = git show --format=%aD | Select-String -First 1

  1. Create and Push the Tag:
    The script creates a signed tag using git tag -s, which includes the tag version and message. It then pushes the tag to the remote repository.

powershell git tag -s $ENV:TAG_VERSION $ENV:TAG_HASH -m $ENV:TAG_MESSAGE git push origin "$ENV:TAG_VERSION"

  1. Cleanup and Return to Main Branch:
    Once the tag has been pushed, the script clears the environment variables and switches back to the main branch.

powershell $ENV:GIT_COMMITTER_DATE = "" git switch main

Conclusion

This script helps you tag old commits with the correct date and push the tags to the remote repository. It's particularly useful when you've missed tagging a release or need to retroactively apply a version tag to a past commit. By using this approach, you can ensure that your repository history remains accurate and consistent.