JENKINS-67725 - Extending BranchBuildStrategies to allow setting last revision built + access to SCMEvent

[carpnick]

See JENKINS-67725 for more context.

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The basic use case:

• How do we enable the folks to "save" the first commit ID found, and only build everything after that. This update allows us to implement a BranchBuildStrategy to do that. Without this change we are not handed the right pieces to implement that use case.

Discussion

• As written this will always evaluate to true even if a BuildStrategy keeps responding, do not build. The next time a branch indexing comes in, it will evaluate to true since it did not build. This feels like a design flaw. As a plugin author I am telling you to not build it. As a Jenkins Admin I am telling you not to build it. But you are repeatedly trying to build it if I turn on branch indexing.
• As I see it we have 2 options
  • We extend BranchBuildStrategy and add another optional method that allows a plugin author to own if you can update the last built hash
  • We create a whole new extension point to give a plugin author the ability to define what changesDetected means.

What is in the PR

• Added a new extension method(optional) for plugin authors can choose to update last built revision or not. Default is false which is current behavior
• Added integration of new method into MultiBranchProject to evaluate if it should update lastbuiltrevision on disk if told not to build.
• Also added SCMEvent to the extension methods. Allows plugin authors to use properties to determine if we should build the artifact. The specific property I am looking for is timestamp. If I create a plugin that requires only building forward(from now) I need to know when the event was generated. This gives me that ability.

Please review at your convenience. This is ready.

[carpnick]

Could I get a review @jtnord and/or @rsandell ?

[carpnick]

Any kind of review would be appreciated...
@timja or @car-roll

[jtnord]

a very quick first pass check seems like this has the potential to break things.

I would also expect at least one downstream PR to demonstrate this new API.

ref: https://www.jenkins.io/doc/developer/extensions/branch-api/#branchbuildstrategy

I need to find some time to go through this in some more detail, but I do not have that time right now,

[jtnord]

this seems like a breaking change? if an Extension overrides this calss and updated to the modern way removing the over ride on this deprecated function - then any consumers that have not updated will not blow up at runtime?

If the extension can do something about it - then it would seem this method is just un-needed - or could be used to call the modern method using the
Util.isOverridden trick.

[carpnick]

I actually followed the example of what the rest of the plugin extension did. IE - Line 111 was originally shipped with 2.0.17 while line 138 was shipped with 2.1.3. Basically everytime there is a new version, the previous version is set to UnsupportedOperationException.

So the way I understand it the SPI method finds out dynamically which method is overridden (original, V2, V3, etc) and then calls that specific override. So the SPI method uses Util.isOverridden to determine which API method to call.

[carpnick]

I would also expect at least one downstream PR to demonstrate this new API.

ref: https://www.jenkins.io/doc/developer/extensions/branch-api/#branchbuildstrategy

Fair comment - I will either do a PR in one of the plugins that exists and/or create a plugin and link it here.