Stabilize new lazy vals (#16614)

Resolve #16555

Author: szymon-rd

community-build/community-projects/scala-parallel-collections

@@ -365,6 +365,7 @@ private sealed trait YSettings:
   val YshowTreeIds: Setting[Boolean] = BooleanSetting("-Yshow-tree-ids", "Uniquely tag all tree nodes in debugging output.")
   val YfromTastyIgnoreList: Setting[List[String]] = MultiStringSetting("-Yfrom-tasty-ignore-list", "file", "List of `tasty` files in jar files that will not be loaded when using -from-tasty")
   val YnoExperimental: Setting[Boolean] = BooleanSetting("-Yno-experimental", "Disable experimental language features")
+  val YlegacyLazyVals: Setting[Boolean] = BooleanSetting("-Ylegacy-lazy-vals", "Use legacy (pre 3.3.0) implementation of lazy vals")
 
   val YprofileEnabled: Setting[Boolean] = BooleanSetting("-Yprofile-enabled", "Enable profiling.")
   val YprofileDestination: Setting[String] = StringSetting("-Yprofile-destination", "file", "Where to send profiling output - specify a file, default is to the console.", "")
@@ -382,7 +383,6 @@ private sealed trait YSettings:
   val YrecheckTest: Setting[Boolean] = BooleanSetting("-Yrecheck-test", "Run basic rechecking (internal test only)")
   val YccDebug: Setting[Boolean] = BooleanSetting("-Ycc-debug", "Used in conjunction with captureChecking language import, debug info for captured references")
   val YccNoAbbrev: Setting[Boolean] = BooleanSetting("-Ycc-no-abbrev", "Used in conjunction with captureChecking language import, suppress type abbreviations")
-  val YlightweightLazyVals: Setting[Boolean] = BooleanSetting("-Ylightweight-lazy-vals", "Use experimental lightweight implementation of lazy vals")
 
   /** Area-specific debug output */
   val YexplainLowlevel: Setting[Boolean] = BooleanSetting("-Yexplain-lowlevel", "When explaining type errors, show types at a lower level.")

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -448,10 +448,10 @@ class LazyVals extends MiniPhase with IdentityDenotTransformer {
 
   def transformMemberDefThreadSafe(x: ValOrDefDef)(using Context): Thicket = {
     assert(!(x.symbol is Mutable))
-    if ctx.settings.YlightweightLazyVals.value then
-      transformMemberDefThreadSafeNew(x)
-    else
+    if ctx.settings.YlegacyLazyVals.value then
       transformMemberDefThreadSafeLegacy(x)
+    else
+      transformMemberDefThreadSafeNew(x)
   }
 
   def transformMemberDefThreadSafeNew(x: ValOrDefDef)(using Context): Thicket = {

compiler/src/dotty/tools/dotc/transform/LazyVals.scala

@@ -38,7 +38,6 @@ null-lazy-val.scala
 patmatch-classtag.scala
 priorityQueue.scala
 serialization-new-legacy.scala
-serialization-new.scala
 singletons.scala
 statics.scala
 stream_flatmap_odds.scala

compiler/test/dotc/run-lazy-vals-tests.allowlist

@@ -597,7 +597,7 @@ class DottyBytecodeTests extends DottyBytecodeTest {
       val clsIn   = dir.lookupName("Test.class", directory = false).input
       val clsNode = loadClassNode(clsIn)
       val method  = getMethod(clsNode, "test")
-      assertEquals(88, instructionsFromMethod(method).size)
+      assertEquals(23, instructionsFromMethod(method).size)
     }
   }
 

compiler/test/dotty/tools/backend/jvm/DottyBytecodeTests.scala

@@ -44,8 +44,8 @@ class CompilationTests {
       compileFilesInDir("tests/pos-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking")),
       compileFilesInDir("tests/pos-custom-args/erased", defaultOptions.and("-language:experimental.erasedDefinitions")),
       compileFilesInDir("tests/pos", defaultOptions.and("-Ysafe-init")),
-      // Run tests for experimental lightweight lazy vals
-      compileFilesInDir("tests/pos", defaultOptions.and("-Ysafe-init", "-Ylightweight-lazy-vals", "-Ycheck-constraint-deps"), FileFilter.include(TestSources.posLazyValsAllowlist)),
+      // Run tests for legacy lazy vals
+      compileFilesInDir("tests/pos", defaultOptions.and("-Ysafe-init", "-Ylegacy-lazy-vals", "-Ycheck-constraint-deps"), FileFilter.include(TestSources.posLazyValsAllowlist)),
       compileFilesInDir("tests/pos-deep-subtype", allowDeepSubtypes),
       compileFilesInDir("tests/pos-custom-args/no-experimental", defaultOptions.and("-Yno-experimental")),
       compileDir("tests/pos-special/java-param-names", defaultOptions.withJavacOnlyOptions("-parameters")),
@@ -212,9 +212,9 @@ class CompilationTests {
       compileDir("tests/run-custom-args/Xmacro-settings/compileTimeEnv", defaultOptions.and("-Xmacro-settings:a,b=1,c.b.a=x.y.z=1,myLogger.level=INFO")),
       compileFilesInDir("tests/run-custom-args/captures", allowDeepSubtypes.and("-language:experimental.captureChecking")),
       compileFilesInDir("tests/run-deep-subtype", allowDeepSubtypes),
-      compileFilesInDir("tests/run", defaultOptions.and("-Ysafe-init"), FileFilter.exclude("serialization-new.scala")),
-      // Run tests for experimental lightweight lazy vals and stable lazy vals.
-      compileFilesInDir("tests/run", defaultOptions.and("-Ysafe-init", "-Ylightweight-lazy-vals", "-Ycheck-constraint-deps"), FileFilter.include(TestSources.runLazyValsAllowlist)),
+      compileFilesInDir("tests/run", defaultOptions.and("-Ysafe-init")),
+      // Run tests for legacy lazy vals.
+      compileFilesInDir("tests/run", defaultOptions.and("-Ysafe-init", "-Ylegacy-lazy-vals", "-Ycheck-constraint-deps"), FileFilter.include(TestSources.runLazyValsAllowlist)),
     ).checkRuns()
   }
 

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -45,28 +45,24 @@ object LazyVals {
 
   /* ------------- Start of public API ------------- */
 
-  @experimental
   sealed trait LazyValControlState
 
   /**
    * Used to indicate the state of a lazy val that is being
    * evaluated and of which other threads await the result.
    */
-  @experimental
   final class Waiting extends CountDownLatch(1) with LazyValControlState
 
   /**
    * Used to indicate the state of a lazy val that is currently being
    * evaluated with no other thread awaiting its result.
    */
-  @experimental
   object Evaluating extends LazyValControlState
 
   /**
    * Used to indicate the state of a lazy val that has been evaluated to
    * `null`.
    */
-  @experimental
   object NullValue extends LazyValControlState
 
   final val BITS_PER_LAZY_VAL = 2L
@@ -86,7 +82,6 @@ object LazyVals {
     unsafe.compareAndSwapLong(t, offset, e, n)
   }
 
-  @experimental
   def objCAS(t: Object, offset: Long, exp: Object, n: Object): Boolean = {
     if (debug)
       println(s"objCAS($t, $exp, $n)")
@@ -147,7 +142,6 @@ object LazyVals {
     r
   }
 
-  @experimental
   def getStaticFieldOffset(field: java.lang.reflect.Field): Long = {
     @nowarn
     val r = unsafe.staticFieldOffset(field)

library/src/scala/runtime/LazyVals.scala

@@ -5,15 +5,6 @@ object MiMaFilters {
   val Library: Seq[ProblemFilter] = Seq(
     ProblemFilters.exclude[MissingClassProblem]("scala.annotation.internal.MappedAlternative"),
 
-    ProblemFilters.exclude[DirectMissingMethodProblem]("scala.runtime.LazyVals.getStaticFieldOffset"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("scala.runtime.LazyVals.objCAS"),
-    ProblemFilters.exclude[MissingClassProblem]("scala.runtime.LazyVals$LazyValControlState"),
-    ProblemFilters.exclude[MissingClassProblem]("scala.runtime.LazyVals$Evaluating$"),
-    ProblemFilters.exclude[MissingClassProblem]("scala.runtime.LazyVals$NullValue$"),
-    ProblemFilters.exclude[MissingClassProblem]("scala.runtime.LazyVals$Waiting"),
-    ProblemFilters.exclude[MissingFieldProblem]("scala.runtime.LazyVals.Evaluating"),
-    ProblemFilters.exclude[MissingFieldProblem]("scala.runtime.LazyVals.NullValue"),
-
     ProblemFilters.exclude[MissingFieldProblem]("scala.runtime.stdLibPatches.language#experimental.into"),
     ProblemFilters.exclude[MissingClassProblem]("scala.runtime.stdLibPatches.language$experimental$into$"),
     ProblemFilters.exclude[MissingFieldProblem]("scala.runtime.stdLibPatches.language#experimental.pureFunctions"),

project/MiMaFilters.scala

@@ -0,0 +1 @@
+-Ylegacy-lazy-vals

tests/printing/transformed/lazy-vals-legacy.flags

@@ -76,16 +76,6 @@ val experimentalDefinitionInLibrary = Set(
   "scala.quoted.Quotes.reflectModule.SymbolModule.newClass",
   "scala.quoted.Quotes.reflectModule.SymbolModule.freshName",
   "scala.quoted.Quotes.reflectModule.SymbolMethods.info",
-
-  // New APIs: Lightweight lazy vals. Can be stabilized in 3.3.0
-  "scala.runtime.LazyVals$.Evaluating",
-  "scala.runtime.LazyVals$.Evaluating$",
-  "scala.runtime.LazyVals$.LazyValControlState",
-  "scala.runtime.LazyVals$.NullValue",
-  "scala.runtime.LazyVals$.NullValue$",
-  "scala.runtime.LazyVals$.Waiting",
-  "scala.runtime.LazyVals$.getStaticFieldOffset",
-  "scala.runtime.LazyVals$.objCAS"
 )