fix scaladoc resolution without JCenter

main/src/main/scala/sbt/Defaults.scala

@@ -2087,18 +2087,17 @@ object Defaults extends BuildCommon {
               val runDoc = Doc.scaladoc(label, s.cacheStoreFactory sub "scala", cs.scalac match {
                 case ac: AnalyzingCompiler => ac.onArgs(exported(s, "scaladoc"))
               }, fiOpts)
-              val isScala3 = ScalaArtifacts.isScala3(sv)
               def isScala3Doc(module: ModuleID): Boolean = {
                 module.configurations.exists(_.startsWith(Configurations.ScalaDocTool.name)) &&
                 module.name == ScalaArtifacts.Scala3DocID
               }
-              if (isScala3 && !allDeps.exists(isScala3Doc)) {
+              if (ScalaArtifacts.isScala3M123(sv) && !allDeps.exists(isScala3Doc)) {
                 Array(
                   "Unresolved scala3doc artifact",
                   "add 'ThisBuild / resolvers += Resolver.JCenterRepository'"
                 ).foreach(m => s.log.error(m))
               }
-              val docSrcs = if (isScala3) tFiles else srcs
+              val docSrcs = if (ScalaArtifacts.isScala3(sv)) tFiles else srcs
               runDoc(docSrcs, cp, out, options, maxErrors.value, s.log)
             case (_, true) =>
               val javadoc =
@@ -3188,10 +3187,11 @@ object Classpaths {
       val sbtOrg = scalaOrganization.value
       val version = scalaVersion.value
       val extResolvers = externalResolvers.value
+      val isScala3M123 = ScalaArtifacts.isScala3M123(version)
       val allToolDeps =
         if (scalaHome.value.isDefined || scalaModuleInfo.value.isEmpty || !managedScalaInstance.value)
           Nil
-        else if (extResolvers.contains(Resolver.JCenterRepository)) {
+        else if (!isScala3M123 || extResolvers.contains(Resolver.JCenterRepository)) {
           ScalaArtifacts.toolDependencies(sbtOrg, version) ++
             ScalaArtifacts.docToolDependencies(sbtOrg, version)
         } else ScalaArtifacts.toolDependencies(sbtOrg, version)

sbt/src/sbt-test/actions/doc-scala3/build.sbt

@@ -1,7 +1,11 @@
-ThisBuild / scalaVersion := "3.0.0-M4-bin-20210212-0273336-NIGHTLY"
-// ThisBuild / scalaVersion := "3.0.0-M3",
-
-lazy val root = (project in file("."))
+lazy val m3 = (project in file("m3"))
   .settings(
+    scalaVersion := "3.0.0-M3",
     resolvers += Resolver.JCenterRepository
   )
+
+lazy val rc1 = (project in file("rc1"))
+  .settings(
+    scalaVersion := "3.0.0-RC1"
+  )
+

sbt/src/sbt-test/actions/doc-scala3/rc1/src/main/scala/foo/A.scala

@@ -0,0 +1,10 @@
+package foo
+
+final val foo="Foo"
+
+object A:
+  /**
+   * @param i An argument
+   */
+  def x(i:Int)=3
+

sbt/src/sbt-test/actions/doc-scala3/test

@@ -1,17 +1,15 @@
-> doc
+> rc1 / doc
 
 # there shouldn't be two api/ directories
 # see https://github.com/lampepfl/dotty/issues/11412
-$ exists target/scala-3.0.0-M4/api/api/index.html
-$ exists target/scala-3.0.0-M4/api/api/foo/A$.html
-$ exists target/scala-3.0.0-M4/api/api/foo.html
+$ exists rc1/target/scala-3.0.0-RC1/api/api/index.html
+$ exists rc1/target/scala-3.0.0-RC1/api/api/foo/A$.html
+$ exists rc1/target/scala-3.0.0-RC1/api/api/foo.html
 
-> ++3.0.0-M3!
-> clean
-> doc
+> m3 / doc
 
 # there shouldn't be two api/ directories
 # see https://github.com/lampepfl/dotty/issues/11412
-$ exists target/scala-3.0.0-M3/api/index.html
-$ exists target/scala-3.0.0-M3/api/api/foo/A$.html
-$ exists target/scala-3.0.0-M3/api/api/foo.html
+$ exists m3/target/scala-3.0.0-M3/api/index.html
+$ exists m3/target/scala-3.0.0-M3/api/api/foo/A$.html
+$ exists m3/target/scala-3.0.0-M3/api/api/foo.html