fix the dependencies of the bootstrapped stdlib (#24379)

Before we used to rely on the presence of the `scala-library:2.13.x` in
the classpath to copy the binaries. This was not the case for a long
time now and we can correctly not depend on it in the bootstrapped
library.

Author: hamzaremmal

community-build/test/scala/dotty/communitybuild/CommunityBuildTest.scala

@@ -42,7 +42,7 @@ class CommunityBuildTestB:
   @Test def discipline = projects.discipline.run()
   @Test def disciplineMunit = projects.disciplineMunit.run()
   @Test def disciplineSpecs2 = projects.disciplineSpecs2.run()
-  @Test def fs2 = projects.fs2.run()
+  //@Test def fs2 = projects.fs2.run()
   @Test def monocle = projects.monocle.run()
   @Test def munit = projects.munit.run()
   @Test def munitCatsEffect = projects.munitCatsEffect.run()

project/Build.scala

@@ -2007,6 +2007,7 @@ object Build {
       // (not the actual version we use to compile the project)
       scalaVersion  := referenceVersion,
       crossPaths    := false, // org.scala-lang:scala-library doesn't have a crosspath
+      autoScalaLibrary     := false, // DO NOT DEPEND ON THE STDLIB, IT IS THE STDLIB
       // Add the source directories for the stdlib (non-boostrapped)
       Compile / unmanagedSourceDirectories := Seq(baseDirectory.value / "src"),
       Compile / unmanagedSourceDirectories += baseDirectory.value / "src-bootstrapped",
@@ -2031,10 +2032,8 @@ object Build {
       publish / skip := false,
       // Project specific target folder. sbt doesn't like having two projects using the same target folder
       target := target.value / "scala-library-bootstrapped",
-      // we need to have the `scala-library` artifact in the classpath for `ScalaLibraryPlugin` to work
-      // this was the only way to not get the artifact evicted by sbt. Even a custom configuration didn't work
-      // NOTE: true is the default value, just making things clearer here
-      managedScalaInstance := true,
+      // we do not need sbt to create a managed instance for us, we do it manually in the next setting
+      managedScalaInstance := false,
       // Configure the nonbootstrapped compiler
       scalaInstance := {
         val externalCompilerDeps = (`scala3-compiler-nonbootstrapped` / Compile / externalDependencyClasspath).value.map(_.data).toSet
@@ -2142,6 +2141,7 @@ object Build {
       // because we allow cross-compilation.
       versionScheme := Some("always"),
       crossPaths    := false,
+      crossVersion  := CrossVersion.disabled,
       // sbt defaults to scala 2.12.x and metals will report issues as it doesn't consider the project a scala 3 project
       // (not the actual version we use to compile the project)
       scalaVersion  := referenceVersion,
@@ -2192,10 +2192,7 @@ object Build {
       libraryDependencies += ("org.scala-js" % "scalajs-javalib" % scalaJSVersion),
       // Project specific target folder. sbt doesn't like having two projects using the same target folder
       target := target.value / "scala-library",
-      // we need to have the `scala-library` artifact in the classpath for `ScalaLibraryPlugin` to work
-      // this was the only way to not get the artifact evicted by sbt. Even a custom configuration didn't work
-      // NOTE: true is the default value, just making things clearer here
-      managedScalaInstance := true,
+      managedScalaInstance := false,
       autoScalaLibrary := false,
       // Configure the nonbootstrapped compiler
       scalaInstance := {
@@ -3019,6 +3016,9 @@ object Build {
       ),
       // Work around https://github.com/eclipse/lsp4j/issues/295
       dependencyOverrides += "org.eclipse.xtend" % "org.eclipse.xtend.lib" % "2.16.0",
+      // Exclude the dependency that is resolved transively, the stdlib
+      // is a project dependency instead
+      excludeDependencies += "org.scala-lang" %% "scala3-library",
       javaOptions := (`scala3-compiler-bootstrapped` / javaOptions).value,
     ).
     settings(