Precise annotation SIP

Author: mbovel

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -256,6 +256,16 @@ object desugar {
           evidenceParamBuf.toList)
   end elimContextBounds
 
+  def isPreciseAnnot(tree: untpd.Tree)(using Context): Boolean =
+    tree match
+      case Apply(Select(New(clsSel), _), Nil) =>
+        inContext(ctx.fresh.setReporter(Reporter.NoReporter).setExploreTyperState()) {
+          try
+            ctx.typer.typedExpr(clsSel).tpe.classSymbol == defn.PreciseAnnot
+          catch case _ : Throwable => false
+        }
+      case _ => false
+
   def addDefaultGetters(meth: DefDef)(using Context): Tree =
 
     /** The longest prefix of parameter lists in paramss whose total number of
@@ -293,14 +303,33 @@ object desugar {
         vparam => toDefParam(vparam, keepAnnotations = true, keepDefault = false)
       }
 
+    // gets arguments should be considered precise
+    val paramPrecises: List[Boolean] =
+      // indication for the type parameters preciseness
+      val preciseMap : Map[TypeName, Boolean] =
+        meth.leadingTypeParams.map(t => (t.name, t.mods.annotations.exists(isPreciseAnnot))).toMap
+      // mapping type parameters preciseness onto term parameter preciseness
+      meth.termParamss.view.flatten.map(p => p.tpt).map {
+        case Ident(n) => preciseMap.getOrElse(n.asTypeName, false)
+        case _ => false
+      }.toList
+
     def defaultGetters(paramss: List[ParamClause], n: Int): List[DefDef] = paramss match
       case ValDefs(vparam :: vparams) :: paramss1 =>
         def defaultGetter: DefDef =
+          val (rhs, tpt) =
+            // if the parameter is precise, then we add explicit return type for the
+            // definition to keep the precise type after precise typing.
+            if paramPrecises(n) then
+              val rhsTyped = withMode(Mode.Precise){ctx.typer.typedExpr(vparam.rhs)}
+              (TypedSplice(rhsTyped), TypeTree(rhsTyped.tpe))
+            // otherwise, the desugaring is unchanged from the status quo
+            else (vparam.rhs, TypeTree())
           DefDef(
             name = DefaultGetterName(meth.name, n),
             paramss = getterParamss(n),
-            tpt = TypeTree(),
-            rhs = vparam.rhs
+            tpt = tpt,
+            rhs = rhs
           )
           .withMods(Modifiers(
             meth.mods.flags & (AccessFlags | Synthetic) | (vparam.mods.flags & Inline),
@@ -381,9 +410,10 @@ object desugar {
 
   @sharable private val synthetic = Modifiers(Synthetic)
 
-  private def toDefParam(tparam: TypeDef, keepAnnotations: Boolean): TypeDef = {
+  private def toDefParam(tparam: TypeDef, keepAnnotations: Boolean)(using Context): TypeDef = {
     var mods = tparam.rawMods
-    if (!keepAnnotations) mods = mods.withAnnotations(Nil)
+    val onlyPreciseAnnot = mods.annotations.filter(isPreciseAnnot)
+    if (!keepAnnotations) mods = mods.withAnnotations(onlyPreciseAnnot)
     tparam.withMods(mods & EmptyFlags | Param)
   }
   private def toDefParam(vparam: ValDef, keepAnnotations: Boolean, keepDefault: Boolean): ValDef = {

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -286,6 +286,17 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
     end recur
 
     val (rtp, paramss) = recur(sym.info, sym.rawParamss)
+    val typeParamsSyms = paramss.view.flatten.filter(_.isType).toList
+    @tailrec def allPrecises(tp: Type, precises: List[Boolean]): List[Boolean] =
+      tp match
+        case pt : PolyType => allPrecises(pt.resType, precises ++ pt.paramPrecises)
+        case mt : MethodType => allPrecises(mt.resType, precises)
+        case _ => precises
+    val paramPrecises = allPrecises(sym.info, Nil)
+    paramPrecises.lazyZip(typeParamsSyms).foreach {
+      case (true, p) => p.addAnnotation(defn.PreciseAnnot)
+      case _ =>
+    }
     DefDef(sym, paramss, rtp, rhsFn(paramss.nestedMap(ref)))
   end DefDef
 

compiler/src/dotty/tools/dotc/cc/Setup.scala

@@ -405,7 +405,7 @@ extends tpd.TreeTraverser:
           info match
             case mt: MethodOrPoly =>
               val psyms = psymss.head
-              mt.companion(mt.paramNames)(
+              mt.companion(mt.paramNames, mt.paramPrecises)(
                 mt1 =>
                   if !psyms.exists(_.isUpdatedAfter(preRecheckPhase)) && !mt.isParamDependent && prevLambdas.isEmpty then
                     mt.paramInfos

compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala

@@ -13,7 +13,7 @@ import typer.ProtoTypes.{newTypeVar, representedParamRef}
 import UnificationDirection.*
 import NameKinds.AvoidNameKind
 import util.SimpleIdentitySet
-
+import annotation.tailrec
 /** Methods for adding constraints and solving them.
  *
  * What goes into a Constraint as opposed to a ConstrainHandler?
@@ -654,8 +654,37 @@ trait ConstraintHandling {
       case WildcardType(optBounds) => optBounds.exists && isSingleton(optBounds.bounds.hi)
       case _ => isSubTypeWhenFrozen(tp, defn.SingletonType)
 
+    def derivesPreciseAnnot(tp: Type): Boolean =
+      tp.derivesAnnotWith(_.matches(defn.PreciseAnnot))
+
+    def dependsOnParam(tp: Type, param: TypeParamRef) : Boolean =
+      tp match
+        case v: TypeVar => v.origin == param
+        case AppliedType(_, args) => args.exists(dependsOnParam(_, param))
+        case _ => false
+
+    def isPreciseRecur(tp: Type, uninstParams : List[TypeParamRef]): Boolean = tp match
+      //the type parameter is annotated as precise or the mode is precise
+      case param: TypeParamRef if param.isPrecise | ctx.mode.is(Mode.Precise) => true
+      //the type parameter is upper-bounded by a precise
+      case param: TypeParamRef if constraint.upper(param).exists(_.isPrecise) => true
+      case param: TypeParamRef =>
+        //the type parameter is from an applied type and there it is annotated as precise
+        constraint.domainLambdas.view.flatMap(_.resType.paramInfoss.flatten).flatMap {
+          case AppliedType(tycon, args) =>
+            val preciseArgIdx = tycon.typeParamSymbols.indexWhere(_.paramPrecise)
+            if (preciseArgIdx >= 0) Some(args(preciseArgIdx) == param)
+            else None
+          case p : TypeParamRef => if (p == param) Some(false) else None
+          case _ => None
+        }.headOption.getOrElse(false)
+      case _ => false
+
+    def isPrecise(tp: Type): Boolean =
+      isPreciseRecur(tp, constraint.uninstVars.view.reverse.map(_.origin).toList)
+
     val wideInst =
-      if isSingleton(bound) then inst
+      if isSingleton(bound) || isPrecise(bound) then inst
       else dropTransparentTraits(widenIrreducible(widenOr(widenSingle(inst))), bound)
     wideInst match
       case wideInst: TypeRef if wideInst.symbol.is(Module) =>

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -133,7 +133,7 @@ class Definitions {
           val underlyingName = name.asSimpleName.drop(6)
           val underlyingClass = ScalaPackageVal.requiredClass(underlyingName)
           denot.info = TypeAlias(
-            HKTypeLambda(argParamNames :+ "R".toTypeName, argVariances :+ Covariant)(
+            HKTypeLambda(argParamNames :+ "R".toTypeName, Nil, argVariances :+ Covariant)(
               tl => List.fill(arity + 1)(TypeBounds.empty),
               tl => CapturingType(underlyingClass.typeRef.appliedTo(tl.paramRefs),
                 CaptureSet.universal)
@@ -187,7 +187,7 @@ class Definitions {
                     useCompleter: Boolean = false) = {
     val tparamNames = PolyType.syntheticParamNames(typeParamCount)
     val tparamInfos = tparamNames map (_ => bounds)
-    def ptype = PolyType(tparamNames)(_ => tparamInfos, resultTypeFn)
+    def ptype = PolyType(tparamNames, Nil)(_ => tparamInfos, resultTypeFn)
     val info =
       if (useCompleter)
         new LazyType {
@@ -719,7 +719,7 @@ class Definitions {
                   case meth: MethodType =>
                     info.derivedLambdaType(
                       resType = meth.derivedLambdaType(
-                      paramNames = Nil, paramInfos = Nil))
+                      paramNames = Nil, paramPrecises = Nil, paramInfos = Nil))
                 }
             }
             val argConstr = constr.copy().entered
@@ -988,6 +988,7 @@ class Definitions {
   @tu lazy val NowarnAnnot: ClassSymbol = requiredClass("scala.annotation.nowarn")
   @tu lazy val TransparentTraitAnnot: ClassSymbol = requiredClass("scala.annotation.transparentTrait")
   @tu lazy val NativeAnnot: ClassSymbol = requiredClass("scala.native")
+  @tu lazy val PreciseAnnot: ClassSymbol = requiredClass("scala.annotation.precise")
   @tu lazy val RepeatedAnnot: ClassSymbol = requiredClass("scala.annotation.internal.Repeated")
   @tu lazy val SourceFileAnnot: ClassSymbol = requiredClass("scala.annotation.internal.SourceFile")
   @tu lazy val ScalaSignatureAnnot: ClassSymbol = requiredClass("scala.reflect.ScalaSignature")

compiler/src/dotty/tools/dotc/core/Denotations.scala

@@ -546,7 +546,7 @@ object Denotations {
              && tp1.isErasedMethod == tp2.isErasedMethod =>
             val resType = infoMeet(tp1.resType, tp2.resType.subst(tp2, tp1), safeIntersection)
             if resType.exists then
-              tp1.derivedLambdaType(mergeParamNames(tp1, tp2), tp1.paramInfos, resType)
+              tp1.derivedLambdaType(mergeParamNames(tp1, tp2), Nil, tp1.paramInfos, resType)
             else NoType
           case _ => NoType
       case tp1: PolyType =>
@@ -556,6 +556,7 @@ object Denotations {
             if resType.exists then
               tp1.derivedLambdaType(
                 mergeParamNames(tp1, tp2),
+                Nil,
                 tp1.paramInfos.zipWithConserve(tp2.paramInfos)( _ & _ ),
                 resType)
             else NoType

compiler/src/dotty/tools/dotc/core/GadtConstraint.scala

@@ -91,7 +91,7 @@ final class ProperGadtConstraint private(
   override def addToConstraint(params: List[Symbol])(using Context): Boolean = {
     import NameKinds.DepParamName
 
-    val poly1 = PolyType(params.map { sym => DepParamName.fresh(sym.name.toTypeName) })(
+    val poly1 = PolyType(params.map { sym => DepParamName.fresh(sym.name.toTypeName) }, params.map(_.paramPrecise))(
       pt => params.map { param =>
         // In bound type `tp`, replace the symbols in dependent positions with their internal TypeParamRefs.
         // The replaced symbols will be later picked up in `ConstraintHandling#addToConstraint`

compiler/src/dotty/tools/dotc/core/Mode.scala

@@ -11,7 +11,7 @@ case class Mode(val bits: Int) extends AnyVal {
   def isExpr: Boolean = (this & PatternOrTypeBits) == None
 
   override def toString: String =
-    (0 until 31).filter(i => (bits & (1 << i)) != 0).map(modeName).mkString("Mode(", ",", ")")
+    (0 until 32).filter(i => (bits & (1 << i)) != 0).map(modeName).mkString("Mode(", ",", ")")
 
   def ==(that: Mode): Boolean = this.bits == that.bits
   def !=(that: Mode): Boolean = this.bits != that.bits
@@ -129,4 +129,9 @@ object Mode {
    *  Type `Null` becomes a subtype of non-primitive value types in TypeComparer.
    */
   val RelaxedOverriding: Mode = newMode(30, "RelaxedOverriding")
+
+  /**
+   * Indication that argument widening should not take place.
+   */
+  val Precise: Mode = newMode(31, "Precise")
 }

compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala

@@ -529,7 +529,7 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
         val TypeBounds(lo, hi) :: pinfos1 = tl.paramInfos: @unchecked
         paramInfos = TypeBounds(lo, LazyRef.of(hi)) :: pinfos1
       }
-      ensureFresh(tl.newLikeThis(tl.paramNames, paramInfos, tl.resultType))
+      ensureFresh(tl.newLikeThis(tl.paramNames, tl.paramPrecises, paramInfos, tl.resultType))
     }
     else tl
 

compiler/src/dotty/tools/dotc/core/ParamInfo.scala

@@ -38,6 +38,9 @@ trait ParamInfo {
   /** The variance of the type parameter */
   def paramVariance(using Context): Variance
 
+  /** The precise enforcement indicator of the type parameter */
+  def paramPrecise(using Context): Boolean
+
   /** The variance of the type parameter, as a number -1, 0, +1.
    *  Bivariant is mapped to 1, i.e. it is treated like Covariant.
    */