[Experiment] Precise annotation

Author: mbovel

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

@@ -293,14 +293,49 @@ object desugar {
         vparam => toDefParam(vparam, keepAnnotations = true, keepDefault = false)
       }
 
+    def ignoreErrorsAndRun[R](op: => R): R =
+      val savedState = ctx.typerState.snapshot()
+      val savedReporter = ctx.reporter
+      ctx.typerState.setReporter(Reporter.NoReporter)
+      val ret = op
+      ctx.typerState.setReporter(savedReporter)
+      ctx.typerState.resetTo(savedState)
+      ret
+
+    // 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 {
+            //TODO: this is a hack. Typing causes problems
+            case Apply(Select(New(Ident(p)), _), _) => p.toString == "precise"
+            case _ => false
+          })
+        ).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),

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

@@ -12,7 +12,7 @@ import config.Printers.typr
 import typer.ProtoTypes.{newTypeVar, representedParamRef}
 import UnificationDirection.*
 import NameKinds.AvoidNameKind
-
+import annotation.tailrec
 /** Methods for adding constraints and solving them.
  *
  * What goes into a Constraint as opposed to a ConstrainHandler?
@@ -545,8 +545,35 @@ 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
+      case param: TypeParamRef if param.isPrecise | ctx.mode.is(Mode.Precise) => 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

@@ -164,7 +164,7 @@ 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 {
@@ -695,7 +695,7 @@ 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
@@ -962,6 +962,7 @@ 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

@@ -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

@@ -523,7 +523,7 @@ 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.
    */

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

@@ -1483,6 +1483,11 @@ object SymDenotations {
       else if is(Contravariant) then Contravariant
       else EmptyFlags
 
+    /** The precise enforcement indicator of this type parameter or type member
+     */
+    final def precise(using Context): Boolean =
+      hasAnnotation(defn.PreciseAnnot)
+
     /** The flags to be used for a type parameter owned by this symbol.
      *  Overridden by ClassDenotation.
      */

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

@@ -346,6 +346,12 @@ object Symbols {
     def paramInfoAsSeenFrom(pre: Type)(using Context): Type = pre.memberInfo(this)
     def paramInfoOrCompleter(using Context): Type = denot.infoOrCompleter
     def paramVariance(using Context): Variance = denot.variance
+    def paramPrecise(using Context): Boolean =
+      val owner = denot.owner
+      if (owner.isConstructor)
+        owner.owner.typeParams.exists(p => p.name == name && p.paramPrecise)
+      else
+        denot.precise
     def paramRef(using Context): TypeRef = denot.typeRef
 
 // -------- Printing --------------------------------------------------------