Merge fa20dd618b into 8bcc6ae420

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

@@ -257,6 +257,7 @@ object Keys {
   val semanticdbIncludeInJar = settingKey[Boolean]("Include *.semanticdb files in published artifacts").withRank(CSetting)
   val semanticdbTargetRoot = settingKey[File]("The output directory to produce META-INF/semanticdb/**/*.semanticdb files").withRank(CSetting)
   val semanticdbOptions = settingKey[Seq[String]]("The Scalac options introduced for SemanticDB").withRank(CSetting)
+  val bestEffortEnabled = settingKey[Boolean]("Enables Scala 3 Best Effort compilation to produce .betasty files").withRank(CSetting)
 
   val clean = taskKey[Unit]("Deletes files produced by the build, such as generated sources, compiled classes, and task caches.").withRank(APlusTask)
   val console = taskKey[Unit]("Starts the Scala interpreter with the project classes on the classpath.").withRank(APlusTask)

main/src/main/scala/sbt/internal/PluginDiscovery.scala

@@ -51,6 +51,7 @@ object PluginDiscovery:
       "sbt.ScriptedPlugin" -> sbt.ScriptedPlugin,
       "sbt.plugins.SbtPlugin" -> sbt.plugins.SbtPlugin,
       "sbt.plugins.SemanticdbPlugin" -> sbt.plugins.SemanticdbPlugin,
+      "sbt.plugins.BestEffortPlugin" -> sbt.plugins.BestEffortPlugin,
       "sbt.plugins.JUnitXmlReportPlugin" -> sbt.plugins.JUnitXmlReportPlugin,
       "sbt.plugins.Giter8TemplatePlugin" -> sbt.plugins.Giter8TemplatePlugin,
       "sbt.plugins.DependencyTreePlugin" -> sbt.plugins.DependencyTreePlugin,

main/src/main/scala/sbt/internal/SysProp.scala

@@ -99,6 +99,7 @@ object SysProp:
   def allowRootDir: Boolean = getOrFalse("sbt.rootdir")
   def legacyTestReport: Boolean = getOrFalse("sbt.testing.legacyreport")
   def semanticdb: Boolean = getOrFalse("sbt.semanticdb")
+  def bestEffort: Boolean = getOrFalse("sbt.bestEffort")
   def forceServerStart: Boolean = getOrFalse("sbt.server.forcestart")
   def serverAutoStart: Boolean = getOrTrue("sbt.server.autostart")
   def remoteCache: Option[URI] = sys.props

main/src/main/scala/sbt/plugins/BestEffortPlugin.scala

@@ -0,0 +1,58 @@
+/*
+ * sbt
+ * Copyright 2023, Scala center
+ * Copyright 2011 - 2022, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt
+package plugins
+
+import Keys.*
+import sbt.internal.SysProp
+import sbt.librarymanagement.syntax.*
+import ProjectExtra.inConfig
+import sbt.internal.inc.ScalaInstance
+
+/**
+ * An AutoPlugin that wires Scala 3's Best Effort compilation into sbt.
+ *
+ * When `bestEffortEnabled` is true and the project uses Scala 3.5+,
+ * `-Ybest-effort` and `-Ywith-best-effort-tasty` are appended to scalacOptions
+ * so that the compiler produces .betasty files (to META-INF/best-effort/ inside classes)
+ * even when compilation fails. These files are consumed by IDEs such as Metals
+ * for improved code intelligence.
+ */
+object BestEffortPlugin extends AutoPlugin:
+  override def requires = SemanticdbPlugin
+  override def trigger = allRequirements
+
+  private val bestEffortFlags = Seq("-Ybest-effort", "-Ywith-best-effort-tasty")
+
+  override lazy val globalSettings: Seq[Def.Setting[?]] = Seq(
+    bestEffortEnabled := SysProp.bestEffort,
+  )
+
+  override lazy val projectSettings: Seq[Def.Setting[?]] =
+    inConfig(Compile)(configurationSettings) ++
+      inConfig(Test)(configurationSettings)
+
+  lazy val configurationSettings: Seq[Def.Setting[?]] = List(
+    scalacOptions := {
+      val orig = scalacOptions.value
+      val enabled = bestEffortEnabled.value
+      val sv = scalaVersion.value
+      if enabled && isScala35Plus(sv) then
+        (orig.filterNot(bestEffortFlags.contains) ++ bestEffortFlags).distinct
+      else orig.filterNot(bestEffortFlags.contains)
+    },
+  )
+
+  private[sbt] def isScala35Plus(scalaVersion: String): Boolean =
+    ScalaInstance.isDotty(scalaVersion) && {
+      val versionPart = scalaVersion.stripPrefix("3.")
+      val minor = versionPart.takeWhile(_.isDigit)
+      minor.nonEmpty && minor.toInt >= 5
+    }
+end BestEffortPlugin

sbt-app/src/sbt-test/project/best-effort-enabled/build.sbt

@@ -0,0 +1,2 @@
+scalaVersion := "3.6.4"
+bestEffortEnabled := true

sbt-app/src/sbt-test/project/best-effort-enabled/changes/ErrorFile.scala

@@ -0,0 +1,8 @@
+object A {
+  val x: Int = 1
+}
+//object B
+val error: Int = "not an int"
+object C {
+  val z: Boolean = true
+}

sbt-app/src/sbt-test/project/best-effort-enabled/changes/FixedFile.scala

@@ -0,0 +1,8 @@
+//object A
+object B {
+  val y: String = "hello"
+}
+//error
+object C {
+  val z: Boolean = true
+}

sbt-app/src/sbt-test/project/best-effort-enabled/src/main/scala/A.scala

@@ -0,0 +1,6 @@
+object A {
+  val x: Int = 1
+}
+object B {
+  val y: String = "hello"
+}

sbt-app/src/sbt-test/project/best-effort-enabled/test

@@ -0,0 +1,18 @@
+# Step 1: Compile succeeds with best effort enabled (Scala 3.5+)
+> compile
+
+# Step 2: Introduce a type error — compile should fail
+$ copy-file changes/ErrorFile.scala src/main/scala/A.scala
+-> compile
+
+# Step 3: Fix the error — compile should succeed again
+$ copy-file changes/FixedFile.scala src/main/scala/A.scala
+> compile
+
+# Step 4: Verify best effort flags are absent for Scala 2
+> set scalaVersion := "2.13.16"
+> show Compile / scalacOptions
+
+# Step 5: Switch back to Scala 3 and verify flags are restored
+> set scalaVersion := "3.6.4"
+> show Compile / scalacOptions