On 03/02/2013, at 9:50 AM, Adam Murdoch wrote:
> Hi,
>
> Something I'd like to try to achieve as part of the work to introduce
> multiple outputs for JVM based projects, is to create fewer task instances at
> configuration time. There are 2 main parts to this:
>
> 1. Don't create tasks that will never be required. For example, if there is
> no src/main/resources directory, and nothing generates it, then don't create
> a processResources task.
> 2. Don't create tasks that are not required for the current build. For
> example, if I'm generating the javadoc, don't create the test task or any of
> its dependencies.
>
> Ignore for the moment how we might do this. Let's just say its possible to
> infer both #1 and #2.
>
> Let's also say that if such as task is directly referenced in the build
> logic, then it's "required". For example, if I execute
> `myTask.dependsOn(processResources)` in my build script, then
> processResources is required and must be created. Possibly also for the
> command-line, so that if I run `gradle processResources`, then it is required.
>
> The question is whether we consider it backwards compatible or not that we
> don't create certain tasks that used to always be created.
>
> At first glance, it looks not too bad. The tasks don't do anything and
> nothing references them from code, so it's fine to leave them out. There are
> a few important benefits to doing this:
>
> - There's less work to do at configuration time.
> - There's less heap required to maintain the model through the whole build.
> - We wouldn't log the execution of tasks that don't do anything. For example,
> if there is no test source, you wouldn't see 'testClasses',
> 'compileTestJava', 'processTestResources' etc.
> - It pushes the decoupling of 'what' and 'how', which means the 'how' can
> vary across different executions of the same build. For example, when
> generated source must be downloaded when building on one platform but can be
> generated when building on some other platform. Or when I'm running the tests
> against a distribution built by CI.
>
> Unfortunately, there are a few places where the tasks leak out and are not
> referenced by name or path:
>
> - Via the events on TaskContainer, such as tasks.all { } or tasks.whenAdded {
> }
> - Iterating over the various collections of tasks, such as
> project.getTasks(name), or tasks.withType(type).
> - Via the execution events, such as gradle.taskGraph.beforeTask { }
>
> Strictly speaking, we'd still be following the contract for these things. In
> practice, though, I think there's an implicit contract that says that we must
> continue to create all possible tasks.
>
> Some options:
>
> 1. Don't create the tasks, and simply document this as a potential breaking
> change (or, more likely, as series of changes).
> 2. Create alternatives to the above leakage points, but with stronger
> contracts. If you use one of the above, then we always create every possible
> task.
> 3. Toggle the strategy based on whether you're using the Gradle 2.0
> configuration model or not.
4. Provide this as a general capability, so that the new language plugins (and
other new/incubating plugins) can take advantage of it. The old language
plugins would extend the new plugins and simply mark their tasks as always
required. Later deprecate and remove the old language plugins.
5. As for #4, but instead of removing the old plugins, change them in Gradle
2.0 so that they no longer mark the tasks as required.
--
Adam Murdoch
Gradle Co-founder
http://www.gradle.org
VP of Engineering, Gradleware Inc. - Gradle Training, Support, Consulting
http://www.gradleware.com
