Move task override tracking from planning time to instantiation time (#4181)

Fixes #4176

- Make overriding of `Discover` mandatory, even in tests, so it always
has useful data
- Propagate `implicitMillDiscover` throughout the module hierarchy
implicitly through `Ctx`
- Combine `Discover#classInfo#declaredTasks#name` together with the
linearization of the Scala trait hierarchy for each module, to decide
whether or not a specific task is overridden or not
- Added a new unit test `optionalOverride` that fails on `main` and
passes on this PR

Also took the opportunity to break up `TestGraphs`, `EvaluationTests`
and `ResolveTests` a bit. Still pretty messy, but better than before

Author: lihaoyi

bsp/src/mill/bsp/BSP.scala

@@ -10,7 +10,7 @@ import mill.scalalib.CoursierModule
 
 object BSP extends ExternalModule with CoursierModule {
 
-  lazy val millDiscover: Discover = Discover[this.type]
+  lazy val millDiscover = Discover[this.type]
 
   private def bspWorkerLibs: T[Agg[PathRef]] = Task {
     millProjectModule("mill-bsp-worker", repositoriesTask())

bsp/worker/src/mill/bsp/worker/MillBuildServer.scala

@@ -38,7 +38,7 @@ private class MillBuildServer(
 
   import MillBuildServer._
 
-  lazy val millDiscover: Discover = Discover[this.type]
+  lazy val millDiscover = Discover[this.type]
 
   private[worker] var cancellator: Boolean => Unit = shutdownBefore => ()
   private[worker] var onSessionEnd: Option[BspServerResult => Unit] = None

contrib/bloop/src/mill/contrib/bloop/BloopImpl.scala

@@ -446,5 +446,5 @@ class BloopImpl(evs: () => Seq[Evaluator], wd: os.Path) extends ExternalModule {
     }
   }
 
-  lazy val millDiscover: Discover = Discover[this.type]
+  lazy val millDiscover = Discover[this.type]
 }

contrib/bloop/test/src/mill/contrib/bloop/BloopTests.scala

@@ -4,6 +4,7 @@ import bloop.config.{Config => BloopConfig}
 import mill._
 import mill.scalajslib.api.ModuleKind
 import mill.scalalib._
+import mill.define.Discover
 import mill.scalanativelib.api.ReleaseMode
 import mill.testkit.UnitTester
 import mill.testkit.TestBaseModule
@@ -78,6 +79,8 @@ object BloopTests extends TestSuite {
       def scalaVersion = "2.12.8"
       override def skipBloop: Boolean = true
     }
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   def readBloopConf(jsonFile: String) =

contrib/buildinfo/test/src/mill/contrib/buildinfo/BuildInfoTests.scala

@@ -5,6 +5,7 @@ import mill.scalalib.ScalaModule
 import mill.scalajslib.ScalaJSModule
 import mill.testkit.UnitTester
 import mill.testkit.TestBaseModule
+import mill.define.Discover
 import os.Path
 import utest._
 
@@ -17,6 +18,8 @@ object BuildInfoTests extends TestSuite {
     def scalaVersion = scalaVersionString
     def buildInfoPackageName = "foo"
     def buildInfoMembers = Seq.empty[BuildInfo.Value]
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   object BuildInfoPlain extends TestBaseModule with BuildInfo with ScalaModule {
@@ -25,6 +28,8 @@ object BuildInfoTests extends TestSuite {
     def buildInfoMembers = Seq(
       BuildInfo.Value("scalaVersion", scalaVersion())
     )
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   object BuildInfoScalaJS extends TestBaseModule with BuildInfo with ScalaJSModule {
@@ -34,6 +39,8 @@ object BuildInfoTests extends TestSuite {
     def buildInfoMembers = Seq(
       BuildInfo.Value("scalaVersion", scalaVersion())
     )
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   object BuildInfoComment extends TestBaseModule with BuildInfo with ScalaModule {
@@ -51,6 +58,8 @@ object BuildInfoTests extends TestSuite {
         comment = "a helpful comment explaining what scalaVersion\nis all about"
       )
     )
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   object BuildInfoStatic extends TestBaseModule with BuildInfo with ScalaModule {
@@ -60,6 +69,8 @@ object BuildInfoTests extends TestSuite {
     def buildInfoMembers = Seq(
       BuildInfo.Value("scalaVersion", scalaVersion())
     )
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   object BuildInfoSettings extends TestBaseModule with BuildInfo with ScalaModule {
@@ -69,13 +80,17 @@ object BuildInfoTests extends TestSuite {
     def buildInfoMembers = Seq(
       BuildInfo.Value("scalaVersion", scalaVersion())
     )
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   object BuildInfoJava extends TestBaseModule with BuildInfo {
     def buildInfoPackageName = "foo"
     def buildInfoMembers = Seq(
       BuildInfo.Value("scalaVersion", "not-provided-for-java-modules")
     )
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   object BuildInfoJavaStatic extends TestBaseModule with BuildInfo {
@@ -84,6 +99,8 @@ object BuildInfoTests extends TestSuite {
     def buildInfoMembers = Seq(
       BuildInfo.Value("scalaVersion", "not-provided-for-java-modules")
     )
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   val testModuleSourcesPath: Path = os.Path(sys.env("MILL_TEST_RESOURCE_DIR")) / "buildinfo"

contrib/docker/test/src/mill/contrib/docker/DockerModuleTest.scala

@@ -3,11 +3,12 @@ package contrib.docker
 
 import mill.scalalib.JavaModule
 import mill.api.Result
+import mill.define.Discover
 import mill.util.TestUtil
 import mill.testkit.UnitTester
 import mill.testkit.TestBaseModule
 import os.Path
-import utest._
+import utest.*
 import utest.framework.TestPath
 
 object DockerModuleTest extends TestSuite {
@@ -47,6 +48,8 @@ object DockerModuleTest extends TestSuite {
     object dockerEnv extends DockerConfig {
       override def dockerEnv = Map("DOCKER_HOST" -> "wrong_host")
     }
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   val testArtifactName = "mill-docker-contrib-test"

contrib/flyway/test/src/mill/contrib/flyway/BuildTest.scala

@@ -1,12 +1,14 @@
 package mill.contrib.flyway
 
-import mill._
-import mill.scalalib._
+import mill.*
+import mill.define.Discover
+import mill.scalalib.*
 import mill.testkit.UnitTester
 import mill.testkit.TestBaseModule
-import utest.{TestSuite, Tests, assert, _}
+import utest.{TestSuite, Tests, assert, *}
 
 object BuildTest extends TestSuite {
+
   object Build extends TestBaseModule {
     object build extends FlywayModule {
 
@@ -18,6 +20,8 @@ object BuildTest extends TestSuite {
       def flywayUrl = "jdbc:h2:mem:test_db;DB_CLOSE_DELAY=-1"
       def flywayDriverDeps = Agg(h2)
     }
+
+    val millDiscover: Discover = Discover[this.type]
   }
 
   def tests = Tests {

contrib/gitlab/test/src/mill/contrib/gitlab/GitlabModuleTests.scala

@@ -2,12 +2,13 @@ package mill.contrib.gitlab
 
 import mill.{T, Task}
 import mill.api.Result.Failure
+import mill.define.Discover
 import mill.scalalib.publish.PomSettings
 import mill.testkit.UnitTester
 import mill.testkit.TestBaseModule
 import utest.framework.TestPath
 import utest.{TestSuite, Tests, assertMatch, test}
-
+import mill.main.TokenReaders._
 object GitlabModuleTests extends TestSuite {
 
   val emptyLookup = new GitlabTokenLookup {
@@ -24,6 +25,8 @@ object GitlabModuleTests extends TestSuite {
     override def publishVersion: T[String] = "0.0.1"
 
     override def tokenLookup: GitlabTokenLookup = emptyLookup
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   // GitlabMavenRepository does not need to be a module, but it needs to be invoked from one.
@@ -33,6 +36,8 @@ object GitlabModuleTests extends TestSuite {
       InstanceRepository("https://gl.local")
 
     override def tokenLookup = emptyLookup
+
+    lazy val millDiscover = Discover[this.type]
   }
 
   override def tests: Tests = Tests {

contrib/jmh/test/src/mill/contrib/jmh/JmhModuleTest.scala

@@ -1,12 +1,13 @@
 package mill
 package contrib.jmh
 
+import mill.define.Discover
 import mill.eval.EvaluatorPaths
 import mill.scalalib.ScalaModule
 import mill.testkit.UnitTester
 import mill.testkit.TestBaseModule
 import os.Path
-import utest._
+import utest.*
 import utest.framework.TestPath
 
 object JmhModuleTest extends TestSuite {
@@ -15,6 +16,8 @@ object JmhModuleTest extends TestSuite {
 
     override def scalaVersion = sys.props.getOrElse("TEST_SCALA_2_13_VERSION", ???)
     override def jmhCoreVersion = "1.35"
+
+    lazy val millDiscover = Discover[this.type]
   }
   val testModuleSourcesPath: Path = os.Path(sys.env("MILL_TEST_RESOURCE_DIR")) / "jmh"
 

contrib/playlib/src/mill/playlib/RouteCompilerWorkerModule.scala

@@ -12,5 +12,5 @@ trait RouteCompilerWorkerModule extends Module {
 private[playlib] object RouteCompilerWorkerModule
     extends ExternalModule
     with RouteCompilerWorkerModule {
-  lazy val millDiscover: Discover = Discover[this.type]
+  lazy val millDiscover = Discover[this.type]
 }