Requiring a new validation when Gerrit performs a three way merge when "Allow content merges" is enabled

[Réda Housni Alaoui]

Hi everyone,

5 Minutes ago, I discovered that I was bitten by "Allow content merges" option.

This option is enabled on all of our projects.

Each code review have to pass at least a Jenkins validation before being submitted. We use the Verified label for that.

Yesterday, I uploaded/submitted simultaneously 2 changes altering the same java file.

Before those changes, the file had an unused import that I'll call com.foo.Bar.

In change 1, I added line of code using com.foo.Bar.

In change 2, the import was automatically removed by my IDE.

Both changes passed the Jenkins validation, since each one compiles separately.

The changes were then merged in the same order (1 then 2) without any merge conflict.

The result is a master branch that does not compile anymore :(

I see 2 solutions to prevent this:

1- Disable "Allow content merges" which would lead to more manual work by the devs

2- Tell Gerrit to ask for a new validation when it performs content merges

Is there an existing option for solution 2?

Or could it be the subject of a feature request?

Best regards

[Gert van Dijk]

On Friday, 3 August 2018 10:19:52 UTC+2, Réda Housni Alaoui wrote:

Yesterday, I uploaded/submitted simultaneously 2 changes altering the same java file.

Before those changes, the file had an unused import that I'll call com.foo.Bar.

In change 1, I added line of code using com.foo.Bar.

In change 2, the import was automatically removed by my IDE.

Both changes passed the Jenkins validation, since each one compiles separately.

The changes were then merged in the same order (1 then 2) without any merge conflict.

The result is a master branch that does not compile anymore :(

I see 2 solutions to prevent this:

1- Disable "Allow content merges" which would lead to more manual work by the devs

2- Tell Gerrit to ask for a new validation when it performs content merges

Is there an existing option for solution 2?

Or could it be the subject of a feature request?

I believe an edit of the same file is not required to trigger this (depending on the project/language perhaps). Let's say you have change that renames a class in <dep.file> in change1 and you add a "from dep import myclass" in <other.file> in unrelated change2, you could break it too. Hence, allowing/disallowing content merges does not fully solve it.

A broader discussion here: https://groups.google.com/d/msg/repo-discuss/O2KIkHEoU38/OFnwBexyAQAJ

Personally, I would put my bet on the unreleased 'batch' plugin that will solve this by the roots. :-)

HTH

[Réda Housni Alaoui]

Thank you Gert.

Can't wait for this batch plugin then :)

[Jan Kundrát]

You might want to check out Zuul and its gating:

https://zuul-ci.org/docs/zuul/user/gating.html

Cheers,
Jan

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[Jonathan Nieder]

See also the workflow using the Commit-Queue label that is used on https://chromium-review.googlesource.com/, for example. To get the property you're looking for, you'll need some mutual exclusion for submits, for example by using the "fast-forward only" merge strategy. This tends to work best if your CI is responsible for doing the final submit, since it can arrange for there to be no contention on submits.

Relevant bug in the bug tracker: https://crbug.com/gerrit/3751

Recent mailing list discussion: https://groups.google.com/d/msg/repo-discuss/O2KIkHEoU38/OFnwBexyAQAJ

Thanks and hope that helps,

Jonathan

Jan Kundrát wrote:

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[MartinFick]

On Friday, August 3, 2018 at 7:02:39 AM UTC-6, Réda Housni Alaoui wrote:

Thank you Gert.

Can't wait for this batch plugin then :)

Here you go:  https://groups.google.com/d/msg/repo-discuss/N6b2c4JbCkQ/oay-lYkjAAAJ

-Martin

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