Clean up Discover macro and codegen (#4461)

* Make `Discover` return a `class` (that can be evolved by adding
fields) rather than a `Tuple` (which cannot)
* Simplify handling of `millDiscover` flags, in particular we do not
need them to be defined for subfolder base modules
* Remove unused `ObjectDataInstrument`, `Snippet`, `ObjectData`
* Remove `MILL_SPLICED_CODE_START_MARKER`

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

Author: lihaoyi

integration/failure/root-subfolder-module-collision/src/RootSubfolderModuleCollisionTests.scala

@@ -10,10 +10,9 @@ object RootSubfolderModuleCollisionTests extends UtestIntegrationTestSuite {
       import tester._
       val res = eval(("resolve", "_"))
       assert(res.isSuccess == false)
-      assert(res.err.contains("cannot override final member"))
-      assert(res.err.contains(
-        " final lazy val sub: _root_.build_.sub.package_.type = _root_.build_.sub.package_ // subfolder module referenc"
-      ))
+      assert(res.err.contains("Reference to sub is ambiguous."))
+      assert(res.err.contains("It is both defined in class package_"))
+      assert(res.err.contains("and inherited subsequently in class package_"))
     }
   }
 }

integration/failure/subfolder-missing-build-prefix/resources/build.mill

@@ -3,7 +3,7 @@ package mill.integration
 import mill.testkit.UtestIntegrationTestSuite
 import utest._
 
-object DocAnnotationsTests extends UtestIntegrationTestSuite {
+object InspectTests extends UtestIntegrationTestSuite {
   def globMatches(glob: String, input: String): Boolean = {
     StringContext
       .glob(

integration/failure/subfolder-missing-build-prefix/resources/sub/package.mill

@@ -5,24 +5,27 @@ import $packages._
 import $file.foo.Box
 import $file.foo.{given Box[Int]}
 
+
+given Cross.ToSegments[DayValue](d => List(d.toString))
+
+given mainargs.TokensReader.Simple[DayValue] with
+  def shortName = "day"
+
+  def read(strs: Seq[String]) =
+    try
+      Right(DayValue.valueOf(strs.head))
+    catch
+      case _: Exception => Left("not a day")
+
+enum DayValue:
+  case Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday
+
 object `package` extends RootModule:
 
   def someTopLevelCommand(): Command[Unit] = Task.Command:
     println(s"Hello, world! ${summon[Box[Int]]} ${build.sub.subTask()}")
   end someTopLevelCommand
 
-  given Cross.ToSegments[DayValue](d => List(d.toString))
-
-  given mainargs.TokensReader.Simple[DayValue] with
-    def shortName = "day"
-    def read(strs: Seq[String]) =
-      try
-        Right(DayValue.valueOf(strs.head))
-      catch
-        case _: Exception => Left("not a day")
-
-  enum DayValue:
-    case Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday
 
   object day extends Cross[DayModule](DayValue.values.toSeq)
 

integration/failure/subfolder-missing-build-prefix/src/SubfolderMissingBuildPrefix.scala

@@ -14,30 +14,13 @@ import scala.collection.mutable
  * the `Task.Command` methods we find. This mapping from `Class[_]` to `MainData`
  * can then be used later to look up the `MainData` for any module.
  */
-case class Discover private (
-    value: Map[
-      Class[_],
-      (Seq[String], Seq[mainargs.MainData[_, _]], Seq[String])
-    ],
-    dummy: Int = 0 /* avoid conflict with Discover.apply(value: Map) below*/
-) {
-  @deprecated("Binary compatibility shim", "Mill 0.11.4")
-  private[define] def this(value: Map[Class[_], Seq[mainargs.MainData[_, _]]]) =
-    this(value.view.mapValues((Nil, _, Nil)).toMap)
-  @deprecated("Binary compatibility shim", "Mill 0.11.4")
-  private[define] def copy(value: Map[Class[_], Seq[mainargs.MainData[_, _]]]): Discover = {
-    new Discover(value.view.mapValues((Nil, _, Nil)).toMap, dummy)
-  }
-}
+class Discover(val classInfo: Map[Class[_], Discover.Node], val allNames: Seq[String])
 
 object Discover {
-  def apply2[T](value: Map[Class[_], (Seq[String], Seq[mainargs.MainData[_, _]], Seq[String])])
-      : Discover =
-    new Discover(value)
-
-  @deprecated("Binary compatibility shim", "Mill 0.11.4")
-  def apply[T](value: Map[Class[_], Seq[mainargs.MainData[_, _]]]): Discover =
-    new Discover(value.view.mapValues((Nil, _, Nil)).toMap)
+  class Node(
+      val entryPoints: Seq[mainargs.MainData[_, _]],
+      val declaredNames: Seq[String]
+  )
 
   inline def apply[T]: Discover = ${ Router.applyImpl[T] }
 
@@ -46,7 +29,7 @@ object Discover {
     import mainargs.Macros.*
     import scala.util.control.NonFatal
 
-    def applyImpl[T: Type](using Quotes): Expr[Discover] = {
+    def applyImpl[T: Type](using quotes: Quotes): Expr[Discover] = {
       import quotes.reflect.*
       val seen = mutable.Set.empty[TypeRepr]
       val moduleSym = Symbol.requiredClass("mill.define.Module")
@@ -62,10 +45,8 @@ object Discover {
           } {
             rec(memberTpe)
             memberTpe.asType match {
-              case '[mill.define.Cross[m]] =>
-                rec(TypeRepr.of[m])
-              case _ =>
-                () // no cross argument to extract
+              case '[mill.define.Cross[m]] => rec(TypeRepr.of[m])
+              case _ => () // no cross argument to extract
             }
           }
         }
@@ -107,89 +88,91 @@ object Discover {
             )
         )
 
+      def sortedMethods(curCls: TypeRepr, sub: TypeRepr, methods: Seq[Symbol]): Seq[Symbol] =
+        for {
+          m <- methods.toList.sortBy(_.fullName)
+          mType = curCls.memberType(m)
+          returnType = methodReturn(mType)
+          if returnType <:< sub
+        } yield m
+
       // Make sure we sort the types and methods to keep the output deterministic;
       // otherwise the compiler likes to give us stuff in random orders, which
       // causes the code to be generated in random order resulting in code hashes
       // changing unnecessarily
-      val mapping = for {
+      val mapping: Seq[(Expr[(Class[_], Node)], Seq[String])] = for {
         discoveredModuleType <- seen.toSeq.sortBy(_.typeSymbol.fullName)
         curCls = discoveredModuleType
         methods = filterDefs(curCls.typeSymbol.methodMembers)
         declMethods = filterDefs(curCls.typeSymbol.declaredMethods)
-        overridesRoutes = {
+        _ = {
           assertParamListCounts(
             curCls,
             methods,
             (TypeRepr.of[mill.define.Command[?]], 1, "`Task.Command`"),
             (TypeRepr.of[mill.define.Target[?]], 0, "Target")
           )
+        }
 
-          def sortedMethods(sub: TypeRepr, methods: Seq[Symbol] = methods): Seq[Symbol] =
-            for {
-              m <- methods.toList.sortBy(_.fullName)
-              mType = curCls.memberType(m)
-              returnType = methodReturn(mType)
-              if returnType <:< sub
-            } yield m
-
-          Tuple3(
-            for {
-              m <- sortedMethods(sub = TypeRepr.of[mill.define.NamedTask[?]])
-            } yield m.name, // .decoded // we don't need to decode the name in Scala 3
-            for {
-              m <- sortedMethods(sub = TypeRepr.of[mill.define.Command[?]])
-            } yield curCls.asType match {
-              case '[t] =>
-                val expr =
-                  try
-                    createMainData[Any, t](
-                      m,
-                      m.annotations.find(_.tpe =:= TypeRepr.of[mainargs.main]).getOrElse('{
-                        new mainargs.main()
-                      }.asTerm),
-                      m.paramSymss
-                    ).asExprOf[mainargs.MainData[?, ?]]
-                  catch {
-                    case NonFatal(e) =>
-                      val (before, Array(after, _*)) = e.getStackTrace().span(e =>
-                        !(e.getClassName() == "mill.define.Discover$Router$" && e.getMethodName() == "applyImpl")
-                      ): @unchecked
-                      val trace =
-                        (before :+ after).map(_.toString).mkString("trace:\n", "\n", "\n...")
-                      report.errorAndAbort(
-                        s"Error generating maindata for ${m.fullName}: ${e}\n$trace",
-                        m.pos.getOrElse(Position.ofMacroExpansion)
-                      )
-                  }
-                // report.warning(s"generated maindata for ${m.fullName}:\n${expr.asTerm.show}", m.pos.getOrElse(Position.ofMacroExpansion))
-                expr
-            },
-            for
-              m <- sortedMethods(sub = TypeRepr.of[mill.define.Task[?]], methods = declMethods)
-            yield m.name.toString
-          )
+        names =
+          sortedMethods(curCls, sub = TypeRepr.of[mill.define.NamedTask[?]], methods).map(_.name)
+        entryPoints = for {
+          m <- sortedMethods(curCls, sub = TypeRepr.of[mill.define.Command[?]], methods)
+        } yield curCls.asType match {
+          case '[t] =>
+            val expr =
+              try
+                createMainData[Any, t](
+                  m,
+                  m.annotations.find(_.tpe =:= TypeRepr.of[mainargs.main]).getOrElse('{
+                    new mainargs.main()
+                  }.asTerm),
+                  m.paramSymss
+                ).asExprOf[mainargs.MainData[?, ?]]
+              catch {
+                case NonFatal(e) =>
+                  val (before, Array(after, _*)) = e.getStackTrace().span(e =>
+                    !(e.getClassName() == "mill.define.Discover$Router$" && e.getMethodName() == "applyImpl")
+                  ): @unchecked
+                  val trace =
+                    (before :+ after).map(_.toString).mkString("trace:\n", "\n", "\n...")
+                  report.errorAndAbort(
+                    s"Error generating maindata for ${m.fullName}: ${e}\n$trace",
+                    m.pos.getOrElse(Position.ofMacroExpansion)
+                  )
+              }
+            expr
         }
-        if overridesRoutes._1.nonEmpty || overridesRoutes._2.nonEmpty || overridesRoutes._3.nonEmpty
+        declaredNames =
+          sortedMethods(
+            curCls,
+            sub = TypeRepr.of[mill.define.NamedTask[?]],
+            declMethods
+          ).map(_.name)
+        if names.nonEmpty || entryPoints.nonEmpty
       } yield {
-        val (names, mainDataExprs, taskNames) = overridesRoutes
         // by wrapping the `overridesRoutes` in a lambda function we kind of work around
         // the problem of generating a *huge* macro method body that finally exceeds the
         // JVM's maximum allowed method size
         val overridesLambda = '{
-          def triple() = (${ Expr(names) }, ${ Expr.ofList(mainDataExprs) }, ${ Expr(taskNames) })
+          def triple() =
+            new Node(${ Expr.ofList(entryPoints) }, ${ Expr(declaredNames) })
           triple()
         }
         val lhs =
           Ref(defn.Predef_classOf).appliedToType(discoveredModuleType.widen).asExprOf[Class[?]]
-        '{ $lhs -> $overridesLambda }
+        ('{ $lhs -> $overridesLambda }, names)
       }
 
       val expr: Expr[Discover] =
         '{
           // TODO: we can not import this here, so we have to import at the use site now, or redesign?
           // import mill.main.TokenReaders.*
           // import mill.api.JsonFormatters.*
-          Discover.apply2(Map(${ Varargs(mapping) }*))
+          new Discover(
+            Map[Class[_], Node](${ Varargs(mapping.map(_._1)) }*),
+            ${ Expr(mapping.iterator.flatMap(_._2).distinct.toList.sorted) }
+          )
         }
       // TODO: if needed for debugging, we can re-enable this
       // report.warning(s"generated discovery for ${TypeRepr.of[T].show}:\n${expr.asTerm.show}", TypeRepr.of[T].typeSymbol.pos.getOrElse(Position.ofMacroExpansion))

integration/feature/docannotations/resources/build.mill renamed to integration/feature/inspect/resources/build.mill

@@ -160,9 +160,9 @@ object Resolve {
       nullCommandDefaults: Boolean,
       allowPositionalCommandArgs: Boolean
   ): Iterable[Either[String, Command[_]]] = for {
-    (cls, (names, entryPoints, _)) <- discover.value
+    (cls, node) <- discover.classInfo
     if cls.isAssignableFrom(target.getClass)
-    ep <- entryPoints
+    ep <- node.entryPoints
     if ep.name == name
   } yield {
     def withNullDefault(a: mainargs.ArgSig): mainargs.ArgSig = {
@@ -303,7 +303,7 @@ trait Resolve[T] {
       ) match {
         case ResolveCore.Success(value) => Right(value)
         case ResolveCore.NotFound(segments, found, next, possibleNexts) =>
-          val allPossibleNames = rootModule.millDiscover.value.values.flatMap(_._1).toSet
+          val allPossibleNames = rootModule.millDiscover.allNames.toSet
           Left(ResolveNotFoundHandler(
             selector = sel,
             segments = segments,