Add the possibility to create a typeSymbol in the Quotes API

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

@@ -2649,6 +2649,16 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
       def newBind(owner: Symbol, name: String, flags: Flags, tpe: TypeRepr): Symbol =
         checkValidFlags(flags.toTermFlags, Flags.validBindFlags)
         dotc.core.Symbols.newSymbol(owner, name.toTermName, flags | dotc.core.Flags.Case, tpe)
+
+      def newTypeAlias(owner: Symbol, name: String, flags: Flags, tpe: TypeRepr, privateWithin: Symbol): Symbol =
+        checkValidFlags(flags.toTypeFlags, Flags.validTypeAliasFlags)
+        assert(!tpe.isInstanceOf[Types.TypeBounds], "Passed `tpe` into newTypeAlias should not represent TypeBounds")
+        dotc.core.Symbols.newSymbol(owner, name.toTypeName, flags | dotc.core.Flags.Deferred, dotc.core.Types.TypeAlias(tpe), privateWithin)
+
+      def newBoundedType(owner: Symbol, name: String, flags: Flags, tpe: TypeBounds, privateWithin: Symbol): Symbol =
+        checkValidFlags(flags.toTypeFlags, Flags.validBoundedTypeFlags)
+        dotc.core.Symbols.newSymbol(owner, name.toTypeName, flags, tpe, privateWithin)
+
       def noSymbol: Symbol = dotc.core.Symbols.NoSymbol
 
       private inline def checkValidFlags(inline flags: Flags, inline valid: Flags): Unit =
@@ -2989,6 +2999,13 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
 
       // Keep: aligned with Quotes's `newBind` doc
       private[QuotesImpl] def validBindFlags: Flags = Case // Flags that could be allowed: Implicit | Given | Erased
+
+      // Keep: aligned with Quotes's 'newBoundedType' doc
+      private[QuotesImpl] def validBoundedTypeFlags: Flags = Private | Protected | Override | Deferred | Final | Infix | Local
+
+      // Keep: aligned with Quotes's `newTypeAlias` doc
+      private[QuotesImpl] def validTypeAliasFlags: Flags = Private | Protected | Override | Final | Infix | Local
+
     end Flags
 
     given FlagsMethods: FlagsMethods with

library/src/scala/quoted/Quotes.scala

@@ -3963,6 +3963,42 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
       // Keep: `flags` doc aligned with QuotesImpl's `validBindFlags`
       def newBind(parent: Symbol, name: String, flags: Flags, tpe: TypeRepr): Symbol
 
+      /** Generate a new type symbol for a type alias with the given parent, name and type
+        *
+        *  This symbol starts without an accompanying definition.
+        *  It is the meta-programmer's responsibility to provide exactly one corresponding definition by passing
+        *  this symbol to the TypeDef constructor.
+        *
+        *  @param parent The owner of the type
+        *  @param name The name of the type
+        *  @param flags extra flags to with which symbol can be constructed. Can be `Private` | `Protected` | `Override` | `Final` | `Infix` | `Local`
+        *  @param tpe The rhs the type alias
+        *  @param privateWithin the symbol within which this new type symbol should be private. May be noSymbol.
+        *  @note As a macro can only splice code into the point at which it is expanded, all generated symbols must be
+        *        direct or indirect children of the reflection context's owner.
+        */
+      @experimental
+      // Keep: `flags` doc aligned with QuotesImpl's `validTypeAliasFlags`
+      def newTypeAlias(parent: Symbol, name: String, flags: Flags, tpe: TypeRepr, privateWithin: Symbol): Symbol
+
+      /** Generate a new type symbol for a type bounds with the given parent, name and type
+        *
+        *  This symbol starts without an accompanying definition.
+        *  It is the meta-programmer's responsibility to provide exactly one corresponding definition by passing
+        *  this symbol to the TypeDef constructor.
+        *
+        *  @param parent The owner of the type
+        *  @param name The name of the type
+        *  @param flags extra flags to with which symbol can be constructed. `Deferred` flag will be added. Can be `Private` | `Protected` | `Override` | `Deferred` | `Final` | `Infix` | `Local`
+        *  @param tpe The bounds of the type
+        *  @param privateWithin the symbol within which this new type symbol should be private. May be noSymbol.
+        *  @note As a macro can only splice code into the point at which it is expanded, all generated symbols must be
+        *        direct or indirect children of the reflection context's owner.
+        */
+      @experimental
+      // Keep: `flags` doc aligned with QuotesImpl's `validBoundedTypeFlags`
+      def newBoundedType(parent: Symbol, name: String, flags: Flags, tpe: TypeBounds, privateWithin: Symbol): Symbol
+
       /** Definition not available */
       def noSymbol: Symbol
 

tests/pos-macros/quote-sym-newboundedtype/Macro_1.scala

@@ -0,0 +1,22 @@
+//> using options -experimental -Yno-experimental
+import scala.quoted.*
+
+inline def testMacro = ${ testImpl }
+
+transparent inline def transparentTestMacro = ${ testImpl }
+
+def testImpl(using Quotes): Expr[Object] = {
+    import quotes.reflect.*
+
+    def makeType(owner: Symbol): Symbol =
+      Symbol.newBoundedType(owner, "mytype", Flags.EmptyFlags, TypeBounds.lower(TypeRepr.of[String]), Symbol.noSymbol)
+
+    val typeDef = TypeDef(makeType(Symbol.spliceOwner))
+    // Expr printer does not work here, see comment:
+    // https://github.com/scala/scala3/pull/20347#issuecomment-2096824617
+    assert(typeDef.toString == "TypeDef(mytype,TypeTree[TypeBounds(TypeRef(TermRef(ThisType(TypeRef(NoPrefix,module class java)),object lang),String),TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any))])")
+
+    val clsSymbol = Symbol.newClass(Symbol.spliceOwner, "CLS", List(TypeRepr.of[Object]), sym => List(makeType(sym)), None)
+    val classDef: ClassDef = ClassDef(clsSymbol, List(TypeTree.of[Object]), List(TypeDef(clsSymbol.typeMember("mytype"))))
+    Block(List(classDef), Apply(Select(New(TypeIdent(clsSymbol)), clsSymbol.primaryConstructor), List.empty)).asExprOf[Object]
+}

tests/pos-macros/quote-sym-newboundedtype/Test_2.scala

@@ -0,0 +1,4 @@
+//> using options -experimental -Yno-experimental
+def test =
+  testMacro
+  transparentTestMacro

tests/pos-macros/quote-sym-newtype-in-trait/Macro_1.scala

@@ -0,0 +1,18 @@
+//> using options -experimental -Yno-experimental
+import scala.quoted.*
+
+inline def testMacro = ${ testImpl }
+
+transparent inline def transparentTestMacro = ${ testImpl }
+
+def testImpl(using Quotes): Expr[Object] = {
+  import quotes.reflect.*
+
+  def makeType(owner: Symbol): Symbol =
+    Symbol.newTypeAlias(owner, "mytype", Flags.EmptyFlags, TypeRepr.of[String], Symbol.noSymbol)
+
+  val clsSymbol = Symbol.newClass(Symbol.spliceOwner, "CLS", List(TypeRepr.of[Object]), sym => List(makeType(sym)), None)
+  val classDef: ClassDef = ClassDef(clsSymbol, List(TypeTree.of[Object]), List(TypeDef(clsSymbol.typeMember("mytype"))))
+
+  Block(List(classDef), Apply(Select(New(TypeIdent(clsSymbol)), clsSymbol.primaryConstructor), List.empty)).asExprOf[Object]
+}

tests/pos-macros/quote-sym-newtype-in-trait/Test_2.scala

@@ -0,0 +1,4 @@
+//> using options -experimental -Yno-experimental
+def test =
+  testMacro
+  transparentTestMacro

tests/pos-macros/quote-sym-newtype/Macro_1.scala

@@ -0,0 +1,13 @@
+//> using options -experimental -Yno-experimental
+import scala.quoted.*
+
+inline def testMacro = ${ testImpl }
+
+def testImpl(using Quotes): Expr[Unit] = {
+    import quotes.reflect.*
+    val sym = Symbol.newTypeAlias(Symbol.spliceOwner, "mytype", Flags.EmptyFlags, TypeRepr.of[String], Symbol.noSymbol)
+    val typeDef = TypeDef(sym)
+    assert(typeDef.show == "type mytype = java.lang.String")
+
+    Block(List(typeDef), '{()}.asTerm).asExprOf[Unit]
+}

tests/pos-macros/quote-sym-newtype/Test_2.scala

@@ -0,0 +1,2 @@
+//> using options -experimental -Yno-experimental
+def test = testMacro

tests/run-tasty-inspector/stdlibExperimentalDefinitions.scala

@@ -63,6 +63,9 @@ val experimentalDefinitionInLibrary = Set(
   "scala.quoted.Quotes.reflectModule.SymbolModule.newModule",
   "scala.quoted.Quotes.reflectModule.SymbolModule.freshName",
   "scala.quoted.Quotes.reflectModule.SymbolMethods.info",
+  // Added for 3.6.0, stabilize after feedback.
+  "scala.quoted.Quotes.reflectModule.SymbolModule.newBoundedType",
+  "scala.quoted.Quotes.reflectModule.SymbolModule.newTypeAlias",
 
   // New feature: functions with erased parameters.
   // Need erasedDefinitions enabled.