fix(gerrit): defer change creation to createPr()

[felipecrs]

TODOs

• Refactor how labels are handled when updating a change, there's no need to pass them as push options in that case as it's very unlikely to fail and also introduce code hacks
• Add prTitle to all commitAndPush calls (very important, as otherwise changes could be created with a different title and Renovate no longer find it)
• Add a warning when updatePr in Gerrit is called with prTitle. That should never happen and this warning may help find spots where commitAndPush is not pushing the commit with the correct prTitle
• Consider making prTitle mandatory for commitAndPush to also avoid that. Edit: No go: in many cases the prTitle itself is undefined. It would require too much changes.
• Test everything again

Changes

The thing is: Gerrit has a very different workflow compared to the other platforms. There is simply no concept of branches for code changes, just the changes themselves.

After a lot of thought, I realized this is the best compromise for the Gerrit platform.

This PR defers the creation of the change to the createPr() method, rather than letting the change be created while preparing the branch.

This is better because it lets the standard Renovate flow continue as usual, and closes a few gaps with the Gerrit platform in Renovate.

This PR also refactors part of #35900 and reverts #38288, as these code hacks outside of the Gerrit platform can now be dropped.

Context

Please select one of the below:

• This closes an existing Issue
  • Closes [Gerrit] Reviewers are no longer (tried) to be assigned #39130
  • Closes `prConcurrentLimit` does not do anything for Gerrit #39152
• This doesn't close an Issue, but I accept the risk that this PR may be closed if maintainers disagree with its opening or implementation

AI assistance disclosure

Did you use AI tools to create any part of this pull request?

Please select one option and, if yes, briefly describe how AI was used (e.g., code, tests, docs) and which tool(s) you used.

• No — I did not use AI for this contribution.
• Yes — minimal assistance (e.g., IDE autocomplete, small code completions, grammar fixes).
• Yes — substantive assistance (AI generated non‑trivial portions of code, tests, or documentation).
• Yes — other (please describe):

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

The public repository: https://review.gerrithub.io/c/felipecrs/renovate-tutorial/+/1226234

[hanson76]

Is this being worked on, we have been forced to pin the version of Renovate to 41.167.0 which is the version prior to the change where Renovate stopped adding reviewers.

Looks like this pr has multiple parts, are all necessary to fix that bug or could it be split into several PRs that could be merged individually?

[felipecrs]

I'll look into completing this PR tomorrow.

[felipecrs]

Sorry, change of plans. I'll look into completing this next week or the other.

[avm99963]

Hey! As requested, I just took a look at the change.

I left some comments that popped up, but both the approach and the entire diff LGTM!

I also thought about an alternative approach while reading your PRs (but I think it is worse than yours):

Renovate's generic action	This PR's approach	An alternative approach
Create a branch	Create a branch locally without pushing	Create a WIP change
Create a PR	Submit a new change to Gerrit	Update the change to be active

It might be helpful to keep this alternative approach in mind in the case that, in the future, Renovate changes in some way such that it requires the branch to exist in the remote after branch creation. Since I don't think this is the case currently, your approach looks much simpler and cleaner!

[felipecrs]

About your alternative approach suggestion:

Renovate has this concept of Draft PRs, which is in my TODO to be implemented in Gerrit through WIP changes.

[avm99963]

Oh, thanks!

[felipecrs]

@avm99963 thanks a lot for your review!