enablePlugins can not find plugin if it is added in subproject

[jobtijhuis]

• I've read the CONTRIBUTING guidelines

If you have a project with a subproject in it the enablePlugins(FooPlugin) cannot find the plugin if it is added in the meta-build of the subproject, while I think this should be the case because sbt is recusive.

Reproduction steps

Create a sbt project with a subproject with the following structure:

project/
  plugins.sbt (empty)
site/
  project/
    plugins.sbt
  build.sbt (sub)
build.sbt (root)

build.sbt (root):

name := "projectwithplugins"

lazy val root = project.in(file(".")).aggregate(site)

lazy val site = project.in(file("site"))

build.sbt (sub) the Play Framework is used as an example of an plugin that needs to be enabled explicitly:

name := "test-site"

enablePlugins(PlayJava)

site/project/plugins.sbt:

// The Play plugin
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.6.16")

If you run sbt on this configuration it will fail with the error:

/home/job/Development/test-enablePlugins/site/build.sbt:3: error: not found: value PlayJava
enablePlugins(PlayJava)

If you then copy the site/project/plugins.sbt to project/plugins.sbt it works, but this is not what is expected.

Problem

enablePlugins can not find plugins added by the meta-build in site/project/plugins.sbt

Expectation

Sbt is recusive and the meta-build builds the definitions for the subprojects build. The meta-build is executed as seen by downloading of packages, but the plugins are then not found by enablePlugins, while you would expect the plugins to be loaded and could be found by enablePlugins.

Notes

sbt version: 1.2.3

[eed3si9n]

Currently sbt recurses into project/ directory, but not the subprojects to discover metabuild.
I don't know if we should keep drilling into directories after directories to achieve this.

What might be interesting would be to come up with a notation where part of the *.sbt is read ahead of time as if it is project/plugin.sbt:

lazy val app = (project in file("."))

@metabuild lazy val plugins = Seq(
  addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.6.16")
)