git-merge-into

Merge a source branch into a specific destination branch

$ git merge-into [source_branch] [destination_branch]

$ git merge-into [destination_branch]

git-merge-into <prefix> [<commit>]

<prefix>
    The path to the subdirectory that represents the subtree within the superproject. This is the directory where the subtree's contents reside.

<commit>
    (Optional) The specific commit or branch from the superproject's history whose changes should be merged into the subtree. If omitted, the script might default to the current HEAD or a predefined reference.

The `git-merge-into` command is typically a helper script, not a core Git command distributed with Git itself. It is often found as a community-contributed utility or part of older `git-subtree` implementations designed to manage sub-repositories within a larger Git project.

Its primary purpose is to integrate changes from the superproject (the main repository) into a specific subdirectory that is being managed as a Git subtree. This process involves effectively creating commits in the subtree's localized history (within the superproject) that reflect changes from the superproject's history. This is particularly useful when you've developed features or fixes in the main project that you wish to propagate back to the original upstream repository of the subtree, allowing the subtree's maintainers to incorporate these updates.

Unlike `git subtree merge`, which pulls changes from the subtree's remote into the superproject, `git-merge-into` facilitates the reverse flow of historical changes into the subtree's representation. Given its non-standard nature, its exact implementation and available options may vary depending on the specific script being used.

• git-merge-into is not a standard Git command. It is typically a custom script or a helper from older `git-subtree` setups. Its availability and behavior may vary significantly.
• Incorrect usage can lead to complex history issues or conflicts within the subtree's history. Users should understand the implications of merging changes across different histories.
• Modern `git subtree` commands (like `git subtree push` for propagating changes) might offer alternative or more robust ways to achieve similar goals without needing a separate `git-merge-into` script.
• Always back up your repository or work on a disposable branch before using non-standard or complex history manipulation commands.

In a typical `git-subtree` workflow, changes made directly within the subtree's directory in the superproject are considered part of the superproject's history. To push these changes (or other superproject changes relevant to the subtree) back to the original upstream repository of the subtree, a common approach is to first "merge" these superproject changes into the subtree's specific history (the part of the superproject's history that corresponds to the subtree). This prepares a clean commit for the subtree that can then be pushed to its remote, making the superproject's changes available to the subtree's independent development.

For propagating changes from the superproject to a subtree's upstream, `git subtree push` is often used. This command effectively squashes the relevant superproject commits into a single commit for the subtree and pushes it. While `git-merge-into` aims to create a more direct merge commit reflecting superproject changes within the subtree's history, `git subtree push` offers a simpler, though potentially less granular, method for synchronization. Alternatively, using `git submodules` or external package managers might be more suitable for managing dependencies in certain scenarios.

The concept behind `git-merge-into` stems from the challenges of managing external dependencies or subprojects in Git before the widespread adoption of `git-submodule` or more robust `git-subtree` implementations. Early solutions often involved custom scripts to handle specific merging or pushing scenarios that were not natively supported or were cumbersome. While `git-subtree` evolved to include commands for pulling and pushing subtree changes, a dedicated `git-merge-into` script emerged in some communities to specifically address the propagation of superproject changes into the subtree's history, often for direct pushing to the subtree's upstream. Its usage has become less common as `git-subtree` and other dependency management tools matured.

git-subtree(1), git-merge(1), git-rebase(1)