Fix #20287: Add flexible types to Quotes library

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

@@ -77,6 +77,7 @@ object Types extends TypeUtils {
    *        |              +- TypeVar
    *        |              +- HKTypeLambda
    *        |              +- MatchType
+   *        |              +- FlexibleType
    *        |
    *        +- GroundType -+- AndType
    *                       +- OrType
@@ -3468,7 +3469,7 @@ object Types extends TypeUtils {
    * `T | Null .. T`, so that `T | Null <: FlexibleType(T) <: T`.
    * A flexible type will be erased to its original type `T`.
    */
-  case class FlexibleType(lo: Type, hi: Type) extends CachedProxyType with ValueType {
+  case class FlexibleType protected(lo: Type, hi: Type) extends CachedProxyType with ValueType {
 
     override def underlying(using Context): Type = hi
 
@@ -3481,7 +3482,7 @@ object Types extends TypeUtils {
   }
 
   object FlexibleType {
-    def apply(tp: Type)(using Context): Type = tp match {
+    def apply(tp: Type)(using Context): FlexibleType = tp match {
       case ft: FlexibleType => ft
       case _ =>
         // val tp1 = tp.stripNull()

compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -2230,7 +2230,7 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
         def isErased: Boolean = false
         def isImplicit: Boolean = self.isImplicitMethod
         def isContextual: Boolean = self.isContextualMethod
-        def methodTypeKind: MethodTypeKind = 
+        def methodTypeKind: MethodTypeKind =
           self.companion match
             case Types.ContextualMethodType => MethodTypeKind.Contextual
             case Types.ImplicitMethodType => MethodTypeKind.Implicit
@@ -2343,6 +2343,27 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
       def unapply(x: NoPrefix): true = true
     end NoPrefix
 
+    type FlexibleType = dotc.core.Types.FlexibleType
+
+    object FlexibleTypeTypeTest extends TypeTest[TypeRepr, FlexibleType]:
+      def unapply(x: TypeRepr): Option[FlexibleType & x.type] = x match
+        case x: (Types.FlexibleType & x.type) => Some(x)
+        case _ => None
+    end FlexibleTypeTypeTest
+
+    object FlexibleType extends FlexibleTypeModule:
+      def apply(tp: TypeRepr): FlexibleType = Types.FlexibleType(tp)
+      def unapply(x: FlexibleType): Some[TypeRepr] = Some(x.hi)
+    end FlexibleType
+
+    given FlexibleTypeMethods: FlexibleTypeMethods with
+      extension (self: FlexibleType)
+        def underlying: TypeRepr = self.hi
+        def lo: TypeRepr = self.lo
+        def hi: TypeRepr = self.hi
+      end extension
+    end FlexibleTypeMethods
+
     type Constant = dotc.core.Constants.Constant
 
     object Constant extends ConstantModule

compiler/src/scala/quoted/runtime/impl/printers/Extractors.scala

@@ -239,6 +239,8 @@ object Extractors {
         this += "NoPrefix()"
       case MatchCase(pat, rhs) =>
         this += "MatchCase(" += pat += ", " += rhs += ")"
+      case FlexibleType(tp) =>
+        this += "FlexibleType(" += tp += ")"
     }
 
     def visitSignature(sig: Signature): this.type = {

compiler/src/scala/quoted/runtime/impl/printers/SourceCode.scala

@@ -1247,6 +1247,11 @@ object SourceCode {
         this += " => "
         printType(rhs)
 
+      case FlexibleType(tp) =>
+        this += "("
+        printType(tp)
+        this += ")?"
+
       case _ =>
         cannotBeShownAsSource(tpe.show(using Printer.TypeReprStructure))
     }

docs/_docs/internals/type-system.md

@@ -36,6 +36,7 @@ Type -+- ProxyType --+- NamedType ----+--- TypeRef
       |              +- TypeVar
       |              +- HKTypeLambda
       |              +- MatchType
+      |              +- FlexibleType
       |
       +- GroundType -+- AndType
                      +- OrType

library/src/scala/quoted/Quotes.scala

@@ -211,7 +211,8 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
    *               +- MatchCase
    *               +- TypeBounds
    *               +- NoPrefix
-   * 
+   *               +- FlexibleType
+   *
    *  +- MethodTypeKind -+- Contextual
    *                     +- Implicit
    *                     +- Plain
@@ -3273,7 +3274,7 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
         def isImplicit: Boolean
         /** Is this the type of parameter clause like `(using X1, ..., Xn)` or `(using x1: X1, x2: X2, ... )` */
         def isContextual: Boolean
-        /** Returns a MethodTypeKind object representing the implicitness of the MethodType parameter clause. */ 
+        /** Returns a MethodTypeKind object representing the implicitness of the MethodType parameter clause. */
         def methodTypeKind: MethodTypeKind
         /** Is this the type of erased parameter clause `(erased x1: X1, ..., xn: Xn)` */
         @deprecated("Use `hasErasedParams` and `erasedParams`", "3.4")
@@ -3428,6 +3429,35 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
       def unapply(x: NoPrefix): true
     }
 
+    // ----- Flexible Type --------------------------------------------
+
+    /** Flexible types for explicit nulls */
+    type FlexibleType <: TypeRepr
+
+    /** `TypeTest` that allows testing at runtime in a pattern match if a `TypeRepr` is a `FlexibleType` */
+    given FlexibleTypeTypeTest: TypeTest[TypeRepr, FlexibleType]
+
+    /** Module object of `type FlexibleType`  */
+    val FlexibleType: FlexibleTypeModule
+
+    /** Methods of the module object `val FlexibleType` */
+    trait FlexibleTypeModule { this: FlexibleType.type =>
+      def apply(tp: TypeRepr): FlexibleType
+      def unapply(x: FlexibleType): Option[TypeRepr]
+    }
+
+    /** Makes extension methods on `FlexibleType` available without any imports */
+    given FlexibleTypeMethods: FlexibleTypeMethods
+
+    /** Extension methods of `FlexibleType` */
+    trait FlexibleTypeMethods:
+      extension (self: FlexibleType)
+        def underlying: TypeRepr
+        def lo: TypeRepr
+        def hi: TypeRepr
+      end extension
+    end FlexibleTypeMethods
+
     ///////////////
     // CONSTANTS //
     ///////////////

project/MiMaFilters.scala

@@ -52,6 +52,9 @@ object MiMaFilters {
       Build.mimaPreviousDottyVersion -> // Seq.empty, // We should never break backwards compatibility
         Seq(
           // `ReversedMissingMethodProblem`s are acceptable. See comment in `Breaking changes since last LTS`.
+          ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule.FlexibleType"),
+          ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule.FlexibleTypeTypeTest"),
+          ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule.FlexibleTypeMethods"),
           ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#SymbolMethods.isSuperAccessor"),
           ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule.MethodTypeKind"),
           ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#MethodTypeModule.apply"),

tests/explicit-nulls/run/tasty-flexible-type.check

@@ -0,0 +1,7 @@
+Inlined(None, Nil, Literal(StringConstant("hello")))
+ConstantType(StringConstant("hello"))
+
+Inlined(None, Nil, Apply(Select(Literal(StringConstant("world")), "trim"), Nil))
+FlexibleType(TypeRef(ThisType(TypeRef(NoPrefix(), "lang")), "String"))
+
+FlexibleType(TypeRef(TermRef(ThisType(TypeRef(NoPrefix(), "java")), "lang"), "String"))

tests/explicit-nulls/run/tasty-flexible-type/quoted_1.scala

@@ -0,0 +1,34 @@
+import scala.quoted.*
+
+object Macros {
+
+  inline def printTree[T](inline x: T): Unit =
+    ${ impl('x) }
+
+  def impl[T](x: Expr[T])(using Quotes): Expr[Unit] = {
+    import quotes.reflect.*
+
+    val tree = x.asTerm
+    val treeStr = Expr(tree.show(using Printer.TreeStructure))
+    val treeTpeStr = Expr(tree.tpe.show(using Printer.TypeReprStructure))
+
+    '{
+      println(${treeStr})
+      println(${treeTpeStr})
+      println()
+    }
+  }
+
+  inline def theTestBlock: Unit = ${ theTestBlockImpl }
+
+  def theTestBlockImpl(using Quotes): Expr[Unit] = {
+    import quotes.reflect.*
+
+    val ft1 = FlexibleType(TypeRepr.of[String])
+    val ft1e = Expr(ft1.show(using Printer.TypeReprStructure))
+
+    '{
+      println(${ft1e})
+    }
+  }
+}

tests/explicit-nulls/run/tasty-flexible-type/quoted_2.scala

@@ -0,0 +1,10 @@
+
+import Macros.*
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    printTree("hello")
+    printTree("world".trim())
+    theTestBlock
+  }
+}