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From Stephen Connolly <>
Subject Re: Reactor safe/rally points
Date Mon, 06 Nov 2017 08:50:32 GMT
Thinking some more, this might be something we could leverage for
incremental builds.

If we save state at the end of each phase (last modified time stamps, hash
of dependencies, etc, also attached artifacts, additional source/resource
roots etc) then, on subsequent builds, if the state file is present and
remains valid then we can skip preceding phases and start that module from
that phase.

In the ideal case that could mean we do nothing with the module as nothing

On Sun 5 Nov 2017 at 17:57, Stephen Connolly <> wrote:

> There are two sets of problems that, assuming we want to fix, both need
> some way to rally a concurrent multimodule build at.
> 1. There is the shade like class of problems, where a plugin wants to
> modify the effective transitive dependencies of a module.
> 2. There is the extensibility class of problems, where people want to
> build a plugin and consume the same plugin in one reactor.
> Now in both cases, I think we can solve a subset of these problems by
> introducing a concept of a rally / safe point in the build plan.
> The mutable model can be solved for reducing scope/ removing
> dependencies... could possibly also allow adding dependencies, provided the
> dependencies are not part of the reactor. The proviso is that the plugin
> goal would need to be marked as a “mutation” goal, and the execution of all
> “mutation” goals for a module defines a safe-point. All downstream modules
> that declare a dependency must be blocked from execution until the
> safe-point is reached.
> Discussion points:
> * how do we handle a build request that will never reach the safe-point,
> eg `mvn test` will not reach package, and hence will not rub shade...
> should we say: fine, no safepoint in build plan, so all good... should we
> say: oops escalate the module with a safe point to `package`?
> * while technically possible to *add* ex-reactor dependencies (if
> ex-reactor they cannot affect the build plan) it could be a bad idea for
> build requests that wouldn’t reach the safepoint, is that reason enough to
> reject addition?
> The extensibility issue is actually an important case. Users want features
> like scripting because they need something custom. Scripting brings back
> imperative builds, which IMHO Maven views as an anti-pattern.
> So what is the problem people are trying to solve? They want a plugin for
> just one project. Right now you cannot because we cannot instantiate the
> full build plan until we can inspect the plugin metadata... but until we
> build the plugin we cannot get the metadata.
> With a general plugin, I think there is not much we can do. For example a
> plugin redefining a lifecycle might actually mean that the build plan will
> be different for modules using that plugin as an extension.
> But if the plugin is just defining some goals and those goals are just
> bound to phases in the pre-existing life cycles... again, it seems we can
> allow the build to proceed
> Discussion points:
> * how to handle `mvn test`. If the plugin is only bound to later phases,
> we are good... but what if the plugin is bound to an early phase? Do we
> just bomb out and say, sorry you need to invoke at least package? Do we
> fall back to local repo? Do we upscale the build plan for the plugin to
> package
> * how to handle `mvn site`... in this case we wouldn’t be producing the
> plugin in the reactor anyway... do we bomb out and say “you must do `mvn
> package site`“? Do we modify the build plan? Do we use local repo?
> * we could be smarter and use the build plan safepoint as a staging point
> and allow lifecycles and other things... though obviously more work
> * what about invoking a plugin goal from the CLI directly... do we ask for
> `mvn package foo:manchu`? For this to work, foo:manchu would have to be an
> aggregator goal, otherwise it could be an execution request on earlier
> modules by a later module? Could we delay the build plan instantiation
> until after the plugin is built? Could we just require the plugin be served
> from the local repository and revalidate the build plan after the new
> plugin build is available?
> I think these are two improvements that could be made *without* changes to
> the modelVersion and they would have a real and meaningful improvement for
> our users... as such I would like us to consider (as optional goals) for
> Maven 4.0.0
> Wdyt?
> --
> Sent from my phone
Sent from my phone

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