Can I Configure Renovate to Rebase a PR with the Target Branch instead of the Basebranch

[BleonLimani]

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Self-hosted Renovate

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Bitbucket Server

Please tell us more about your question or problem

Hello everyone,

Our company recently started using RenovateBot to keep dependencies in our projects up-to-date. However, we are encountering an issue and are not sure how to resolve it or if it's even possible. The renovate.json configuration we are using looks like this:

{
  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
  "enabledManagers": [
    "npm",
    "nuget"
  ],
  "ignoreDeps": [
    "DEP1",
    "DEP2",
    "DEP3"
  ],
  "baseBranches": [
    "/^dev\\/VERSION.*/i"
  ],
  "branchPrefix": "renovate/features/",
  "schedule": [
    "at any time"
  ],
  "recreateWhen": "auto",
  "automerge": false,
  "timezone": "Europe/Berlin",
  "rebaseWhen": "behind-base-branch",
  "labels": [
    "dependencies"
  ],
  "reviewers": [
    "user4",
    "user1"
  ],
  "lockFileMaintenance": {
    "enabled": true,
    "schedule": [
      "at any time"
    ]
  },
  "ignorePaths": [
    "**/SUBMODULE1/**",
    "**/SUBMODULE2/**"
  ],
  "packageRules": [
    {
      "matchDepTypes": [
        "engines",
        "overrides"
      ],
      "enabled": false
    },
    {
      "matchManagers": [
        "npm"
      ],
      "matchUpdateTypes": [
        "patch"
      ],
      "groupName": "npm patch updates",
      "reviewers": [
        "user1",
        "user3"
      ],
      "branchName": "renovate/features/{{depName}}-{{updateType}}"
    },
    {
      "matchManagers": [
        "npm"
      ],
      "matchUpdateTypes": [
        "minor"
      ],
      "groupName": "npm minor updates",
      "reviewers": [
        "user1",
        "user3"
      ],
      "branchName": "renovate/features/{{depName}}-{{updateType}}"
    },
    {
      "matchManagers": [
        "npm"
      ],
      "matchUpdateTypes": [
        "major"
      ],
      "groupName": "npm major updates",
      "reviewers": [
        "user1",
        "user3"
      ],
      "branchName": "renovate/features/{{depName}}-{{updateType}}"
    },
    {
      "matchManagers": [
        "nuget"
      ],
      "matchUpdateTypes": [
        "patch"
      ],
      "groupName": "nuget patch updates",
      "reviewers": [
        "user1",
        "user2"
      ],
      "branchName": "renovate/features/{{depName}}-{{updateType}}"
    },
    {
      "matchManagers": [
        "nuget"
      ],
      "matchUpdateTypes": [
        "minor"
      ],
      "groupName": "nuget minor updates",
      "reviewers": [
        "user1",
        "user2"
      ],
      "branchName": "renovate/features/{{depName}}-{{updateType}}"
    },
    {
      "matchManagers": [
        "nuget"
      ],
      "matchUpdateTypes": [
        "major"
      ],
      "groupName": "nuget major updates",
      "reviewers": [
        "user1",
        "user2"
      ],
      "branchName": "renovate/features/{{depName}}-{{updateType}}"
    }
  ],
  "prHourlyLimit": 4,
  "prConcurrentLimit": 10
}

Our project is hosted on Bitbucket Server, and the defined base branch for this project is develop. The projects we actively work on are under dev/VERSION + {...}. These branches are versioned in ascending order, and we auto-merge changes from the lower versions sequentially into the higher versions. As a result, develop is always up-to-date with the latest dev/VERSION... branch.

I have set rebaseWhen to never because previous attempts with rebasing did not work as expected.

The Issue:
When the bot encounters a conflict in an open PR, it updates the PR and merges the changes from the base branch (develop) into the PR branch. This behavior causes massive diffs in PRs for updates to lower dev/VERSION... versions.

Example:

-> develop
-> dev
     -> VERSION_1
     -> VERSION_2
     -> VERSION_3
     -> VERSION_4

The bot opens a PR: renovate/features/DEP10 -> VERSION_1

The created branch is then based on VERSION_1. If a conflict arises, I would expect the bot to use the target branch for rebasing. However, this does not seem to be the case.

My Question:

Is it possible to adjust the configuration so that the bot exhibits the expected behavior? Specifically, can we configure it to:

1. Rebase or merge using the target branch instead of the base branch (develop) when a conflict occurs?
2. Alternatively, can we instruct the bot to delete the conflicting PR and recreate it based on the target branch?

Thank you!

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