integrate assumedVersionScheme and assumedEvictionErrorLevel

Fixes https://github.com/sbt/sbt/issues/6301
Fixes https://github.com/sbt/sbt/issues/6302

```scala
ThisBuild / assumedVersionScheme := VersionScheme.PVP
ThisBuild / assumedVersionSchemeJava := VersionScheme.EarlySemVer
ThisBuild / assumedEvictionErrorLevel := Level.Warn
```

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

@@ -2785,6 +2785,9 @@ object Classpaths {
         libraryDependencies :== Nil,
         libraryDependencySchemes :== Nil,
         evictionErrorLevel :== Level.Error,
+        assumedEvictionErrorLevel :== Level.Info,
+        assumedVersionScheme :== VersionScheme.Always,
+        assumedVersionSchemeJava :== VersionScheme.Always,
         excludeDependencies :== Nil,
         ivyLoggingLevel := (// This will suppress "Resolving..." logs on Jenkins and Travis.
         if (insideCI.value)
@@ -3592,6 +3595,9 @@ object Classpaths {
       uwConfig = (unresolvedWarningConfiguration in update).value,
       evictionLevel = evictionErrorLevel.value,
       versionSchemeOverrides = libraryDependencySchemes.value,
+      assumedEvictionErrorLevel = assumedEvictionErrorLevel.value,
+      assumedVersionScheme = assumedVersionScheme.value,
+      assumedVersionSchemeJava = assumedVersionSchemeJava.value,
       mavenStyle = publishMavenStyle.value,
       compatWarning = compatibilityWarningOptions.value,
       includeCallers = includeCallers,

main/src/main/scala/sbt/Keys.scala

@@ -458,7 +458,10 @@ object Keys {
   val updateFull = taskKey[UpdateReport]("Resolves and optionally retrieves dependencies, producing a full report with callers.").withRank(CTask)
   val evicted = taskKey[EvictionWarning]("Display detailed eviction warnings.").withRank(CTask)
   val evictionWarningOptions = settingKey[EvictionWarningOptions]("Options on eviction warnings after resolving managed dependencies.").withRank(DSetting)
-  val evictionErrorLevel = settingKey[Level.Value]("The log level for detected eviction errors. Level.Error will throw an error.")
+  val evictionErrorLevel = settingKey[Level.Value]("The log level for the detected eviction errors. Level.Error will throw an error.").withRank(DSetting)
+  val assumedEvictionErrorLevel = settingKey[Level.Value]("The log level for the assumed eviction errors. Level.Error will throw an error.").withRank(DSetting)
+  val assumedVersionScheme = settingKey[String]("The assumed version scheme of a Scala library when POM doesn't have versionScheme.").withRank(DSetting)
+  val assumedVersionSchemeJava = settingKey[String]("The assumed version scheme of a Java library when POM doesn't have versionScheme.").withRank(DSetting)
   val transitiveUpdate = taskKey[Seq[UpdateReport]]("UpdateReports for the internal dependencies of this project.").withRank(DTask)
   val updateClassifiers = TaskKey[UpdateReport]("updateClassifiers", "Resolves and optionally retrieves classified artifacts, such as javadocs and sources, for dependency definitions, transitively.", BPlusTask, update)
   val transitiveClassifiers = settingKey[Seq[String]]("List of classifiers used for transitively obtaining extra artifacts for sbt or declared dependencies.").withRank(BSetting)

main/src/main/scala/sbt/VersionScheme.scala

@@ -0,0 +1,18 @@
+/*
+ * sbt
+ * Copyright 2011 - 2018, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt
+
+import sbt.internal.librarymanagement.VersionSchemes
+
+object VersionScheme {
+  val Always = VersionSchemes.Always
+  val EarlySemVer = VersionSchemes.EarlySemVer
+  val PVP = VersionSchemes.PackVer
+  val SemVerSpec = VersionSchemes.SemVerSpec
+  val Strict = VersionSchemes.Strict
+}

main/src/main/scala/sbt/internal/LibraryManagement.scala

@@ -39,6 +39,9 @@ private[sbt] object LibraryManagement {
       uwConfig: UnresolvedWarningConfiguration,
       evictionLevel: Level.Value,
       versionSchemeOverrides: Seq[ModuleID],
+      assumedEvictionErrorLevel: Level.Value,
+      assumedVersionScheme: String,
+      assumedVersionSchemeJava: String,
       mavenStyle: Boolean,
       compatWarning: CompatibilityWarningOptions,
       includeCallers: Boolean,
@@ -63,18 +66,32 @@ private[sbt] object LibraryManagement {
       val report1 = transform(report)
 
       // Warn of any eviction and compatibility warnings
-      val evictionError = EvictionError(report1, module, versionSchemeOverrides)
+      val evictionError = EvictionError(
-      if (evictionError.incompatibleEvictions.isEmpty) ()
+        report1,
-      else
+        module,
-        evictionLevel match {
+        versionSchemeOverrides,
-          case Level.Error =>
+        assumedVersionScheme,
-            val msgs = List(
+        assumedVersionSchemeJava,
+        assumedEvictionErrorLevel
+      )
+      def extraLines = List(
         "",
         "this can be overridden using libraryDependencySchemes or evictionErrorLevel"
       )
-            sys.error((evictionError.lines ++ msgs).mkString(EOL))
+      val errorLines: Seq[String] =
-          case _ =>
+        (if (evictionError.incompatibleEvictions.isEmpty
-            evictionError.lines.foreach(log.log(evictionLevel, _: String))
+             || evictionLevel != Level.Error) Nil
+         else evictionError.lines) ++
+          (if (evictionError.assumedIncompatibleEvictions.isEmpty
+               || assumedEvictionErrorLevel != Level.Error) Nil
+           else evictionError.toAssumedLines)
+      if (errorLines.nonEmpty) sys.error((errorLines ++ extraLines).mkString(EOL))
+      else {
+        if (evictionError.incompatibleEvictions.isEmpty) ()
+        else evictionError.lines.foreach(log.log(evictionLevel, _: String))
+
+        if (evictionError.assumedIncompatibleEvictions.isEmpty) ()
+        else evictionError.toAssumedLines.foreach(log.log(assumedEvictionErrorLevel, _: String))
       }
       CompatibilityWarning.run(compatWarning, module, mavenStyle, log)
       val report2 = transformDetails(report1, includeCallers, includeDetails)
@@ -272,6 +289,9 @@ private[sbt] object LibraryManagement {
           uwConfig = (unresolvedWarningConfiguration in update).value,
           evictionLevel = Level.Debug,
           versionSchemeOverrides = Nil,
+          assumedEvictionErrorLevel = Level.Debug,
+          assumedVersionScheme = VersionScheme.Always,
+          assumedVersionSchemeJava = VersionScheme.Always,
           mavenStyle = publishMavenStyle.value,
           compatWarning = compatibilityWarningOptions.value,
           includeCallers = false,

project/Dependencies.scala

@@ -14,7 +14,7 @@ object Dependencies {
   // sbt modules
   private val ioVersion = nightlyVersion.getOrElse("1.5.0-M1")
   private val lmVersion =
-    sys.props.get("sbt.build.lm.version").orElse(nightlyVersion).getOrElse("1.5.0-M5")
+    sys.props.get("sbt.build.lm.version").orElse(nightlyVersion).getOrElse("1.5.0-M6")
   val zincVersion = nightlyVersion.getOrElse("1.5.0-M3")
 
   private val sbtIO = "org.scala-sbt" %% "io" % ioVersion