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doc: change backporting guide with updated info #53746

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Sep 18, 2024
149 changes: 58 additions & 91 deletions doc/contributing/backporting-to-release-lines.md
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## Staging branches

Each release line has a staging branch that the releaser will use as a scratch
pad while preparing a release. The branch name is formatted as follows:
`vN.x-staging` where `N` is the major release number.
Each release line has a staging branch that serves as a workspace for preparing releases.
The branch format is `vN.x-staging`, where `N` is the major release number.

For the active staging branches see the [Release Schedule][].
For active staging branches, refer to the [Release Schedule][].

## What needs to be backported?
## Identifying changes that require a backport

If a cherry-pick from `main` does not land cleanly on a staging branch, the
releaser will mark the pull request with a particular label for that release
line (e.g. `backport-requested-vN.x`), specifying to our tooling that this
pull request should not be included. The releaser will then add a comment
requesting that a backport pull request be made.
If a cherry-pick from `main` doesn't apply cleanly on a staging branch, the pull request
will be labeled for the release line (e.g., `backport-requested-vN.x`). This indicates
that manual backporting is required.

## What can be backported?
## Criteria for backporting

The "Current" release line is much more lenient than the LTS release lines in
what can be landed. Our LTS release lines (see the [Release Plan][])
require that commits mature in the Current release for at least 2 weeks before
they can be landed in an LTS staging branch. Only after "maturation" will those
commits be cherry-picked or backported.
The "Current" release line is more flexible than LTS lines. LTS branches, detailed in the [Release Plan][],
require commits to mature in the Current release for at least two weeks before backporting.

## How to label backport issues and PRs?
## Labeling backport issues and PRs

For the following labels, the `N` in `vN.x` refers to the major release number.
Use the following labels, with `N` in `vN.x` denoting the major release number:

| Label | Description |
| ----------------------- | ------------------------------------------------------------------------------------------------- |
| backport-blocked-vN.x | PRs that should land on the vN.x-staging branch but are blocked by another PR's pending backport. |
| backport-open-vN.x | Indicate that the PR has an open backport. |
| backport-requested-vN.x | PRs awaiting manual backport to the vN.x-staging branch. |
| backported-to-vN.x | PRs backported to the vN.x-staging branch. |
| baking-for-lts | PRs that need to wait before landing in a LTS release. |
| lts-watch-vN.x | PRs that may need to be released in vN.x. |
| vN.x | Issues that can be reproduced on vN.x or PRs targeting the vN.x-staging branch. |
| Label | Description |
| ----------------------- | ------------------------------------------------------------------- |
| backport-blocked-vN.x | PRs for `vN.x-staging` blocked by pending backports from other PRs. |
| backport-open-vN.x | Indicates an open backport for the PR. |
| backport-requested-vN.x | PR awaiting manual backport to `vN.x-staging`. |
| backported-to-vN.x | PR successfully backported to `vN.x-staging`. |
| baking-for-lts | PRs awaiting LTS release after maturation in Current. |
| lts-watch-vN.x | PRs possibly included in `vN.x` LTS releases. |
| vN.x | Issues or PRs impacting `vN.x-staging` (or reproducible on vN.x). |

## How to submit a backport pull request
## Submitting a backport pull request

For the following steps, let's assume that you need to backport PR `123`
to the v20.x release line. All commands will use the `v20.x-staging` branch
to the vN.x release line. All commands will use the `vN.x-staging` branch
as the target branch. In order to submit a backport pull request to another
branch, simply replace that with the staging branch for the targeted release
branch, simply replace `N` with the version number for the targeted release
line.

### Automated
### Automated process

1. Make sure you have [`@node-core/utils`][] installed
1. Ensure [`@node-core/utils`][] is installed.

2. Run the [`git node backport`][] command
2. Execute [`git node backport`][] command:

```bash
# Backport PR 123 to v20.x-staging
git node backport 123 --to=20
```
```bash
# Example: Backport PR 123 to vN.x-staging
git node backport 123 --to=N
```

3. Jump to step 5 in the Manual section below
3. Proceed to step 5 in the Manual section below.

### Manually
### Manual process

1. Checkout the staging branch for the targeted release line.
1. Checkout the `vN.x-staging` branch.

2. Make sure that the local staging branch is up to date with the remote.
2. Verify that the local staging branch is up to date with the remote.

3. Create a new branch off of the staging branch, as shown below.
3. Create a new branch based on `vN.x-staging`:

```bash
# Assuming your fork of Node.js is checked out in $NODE_DIR,
# the origin remote points to your fork, and the upstream remote points
# to git@github.com:nodejs/node.git
cd $NODE_DIR
# If v20.x-staging is checked out `pull` should be used instead of `fetch`
git fetch upstream v20.x-staging:v20.x-staging -f
# Assume we want to backport PR #10157
git checkout -b backport-10157-to-v20.x v20.x-staging
# Ensure there are no test artifacts from previous builds
# Note that this command deletes all files and directories
# not under revision control below the ./test directory.
# It is optional and should be used with caution.
git clean -xfd ./test/
git fetch upstream vN.x-staging:vN.x-staging -f
git checkout -b backport-123-to-vN.x vN.x-staging
```

4. After creating the branch, apply the changes to the branch. The cherry-pick
will likely fail due to conflicts. In that case, you will see something
like this:

```console
# Say the $SHA is 773cdc31ef
$ git cherry-pick $SHA # Use your commit hash
error: could not apply 773cdc3... <commit title>
hint: after resolving the conflicts, mark the corrected paths
hint: with 'git add <paths>' or 'git rm <paths>'
hint: and commit the result with 'git commit'
4. Cherry-pick the desired commit(s):

```bash
git cherry-pick <commit hash>
```

5. Make the required changes to remove the conflicts, add the files to the index
using `git add`, and then commit the changes. That can be done with
`git cherry-pick --continue`.
5. Resolve conflicts using `git add` and `git cherry-pick --continue`.

6. Leave the commit message as is. If you think it should be modified, comment
in the pull request. The `Backport-PR-URL` metadata does need to be added to
the commit, but this will be done later.

7. Make sure `make -j4 test` passes.
7. Verify that `make -j4 test` passes.

8. Push the changes to your fork.

9. Open a pull request:
1. Be sure to target the `v20.x-staging` branch in the pull request.
2. Include the backport target in the pull request title in the following
format: `[v20.x backport] <commit title>`.
Example: `[v20.x backport] process: improve performance of nextTick`
3. Check the checkbox labeled "Allow edits and access to secrets by
maintainers".
4. In the description add a reference to the original pull request.
5. Amend the commit message and include a `Backport-PR-URL:` metadata and
re-push the change to your fork.
6. Run a [`node-test-pull-request`][] CI job (with `REBASE_ONTO` set to the
default `<pr base branch>`)

10. Replace the `backport-requested-v20.x` label on the original pull request
with `backport-open-v20.x`.

11. If during the review process conflicts arise, use the following to rebase:
`git pull --rebase upstream v20.x-staging`

After the pull request lands, replace the `backport-open-v20.x` label on the
original pull request with `backported-to-v20.x`.

* Target `vN.x-staging`.
* Title format: `[vN.x backport] <commit title>` (e.g., `[v20.x backport] process: improve performance of nextTick`).
* Reference the original PR in the description.

10. Update the `backport-requested-vN.x` label on the original pull request to `backport-open-vN.x`.

11. If conflicts arise during the review process, the following command be used to rebase:

```bash
git pull --rebase upstream vN.x-staging
```

Once merged, update the original PR's label from `backport-open-vN.x` to `backported-to-vN.x`.

[Release Plan]: https://github.com/nodejs/Release#release-plan
[Release Schedule]: https://github.com/nodejs/Release#release-schedule
[`@node-core/utils`]: https://github.com/nodejs/node-core-utils
[`git node backport`]: https://github.com/nodejs/node-core-utils/blob/main/docs/git-node.md#git-node-backport
[`node-test-pull-request`]: https://ci.nodejs.org/job/node-test-pull-request/build
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