Add defaultParams method to Tasty Reflect Symbol API

Author: anatoliykmetyuk

compiler/src/dotty/tools/dotc/tastyreflect/ReflectionCompilerInterface.scala

@@ -1779,6 +1779,22 @@ class ReflectionCompilerInterface(val rootContext: core.Contexts.Context) extend
       case sym if sym.is(Flags.CaseAccessor) => sym.asTerm
     }
 
+  def Symbol_defaultParams(self: Symbol)(using ctx: Context): Map[String, Ref] =
+    assert(self.isClass && self.flags.is(Flags.Case))
+    val comp: Symbol = self.companionClass
+    val names: List[String] =
+      for p <- Symbol_caseFields(self) if p.flags.is(Flags.HasDefault)
+      yield Symbol_name(p)
+
+    val body = ClassDef_body(Symbol_tree(comp).asInstanceOf[ClassDef])
+    val idents: List[Ref] =
+      for case deff @ DefDef(name, _, _, _, tree) <- body
+      if name.toString.startsWith("$lessinit$greater$default")
+      yield Ref_apply(deff.symbol)
+
+    names.zip(idents).toMap
+  end Symbol_defaultParams
+
   def Symbol_children(self: Symbol)(using ctx: Context): List[Symbol] =
     self.children
 

library/src/scala/tasty/Reflection.scala

@@ -2284,6 +2284,14 @@ class Reflection(private[scala] val internal: CompilerInterface) { self =>
     def caseFields(using ctx: Context): List[Symbol] =
       internal.Symbol_caseFields(sym)
 
+    /** Default parameters of a case class. Keys are names of the parameters and values –
+     *  symbols of the definitions sites of the default values.
+     *  Implementation restriction: only the default parameters in the first parameter group
+     *  are returned.
+     */
+    def defaultParams(using ctx: Context): Map[String, Ref] =
+      internal.Symbol_defaultParams(sym)
+
     def isTypeParam(using ctx: Context): Boolean =
       internal.Symbol_isTypeParam(sym)
 

library/src/scala/tasty/reflect/CompilerInterface.scala

@@ -1332,6 +1332,13 @@ trait CompilerInterface {
   /** Fields of a case class type -- only the ones declared in primary constructor */
   def Symbol_caseFields(self: Symbol)(using ctx: Context): List[Symbol]
 
+  /** Default parameters of a case class. Keys are names of the parameters and values –
+   *  symbols of the definitions sites of the default values.
+   *  Implementation restriction: only the default parameters in the first parameter group
+   *  are returned.
+   */
+  def Symbol_defaultParams(self: Symbol)(using ctx: Context): Map[String, Ref]
+
   def Symbol_of(fullName: String)(using ctx: Context): Symbol
 
   def Symbol_newMethod(parent: Symbol, name: String, flags: Flags, tpe: Type, privateWithin: Symbol)(using ctx: Context): Symbol

tests/run-macros/reflect-defaultParams.check

@@ -0,0 +1 @@
+Map(address -> Home, age -> 1)

tests/run-macros/reflect-defaultParams/Macro_1.scala

@@ -0,0 +1,11 @@
+import scala.quoted._
+
+inline def defaultParams[T]: Map[String, Any] = ${ defaultParamsImpl[T] }
+private def defaultParamsImpl[T](
+  using tpe: Type[T], qctx: QuoteContext): Expr[Map[String, Any]] =
+  import qctx.tasty._
+  val sym = tpe.unseal.symbol
+  val exprs: Map[String, Expr[Any]] =
+    sym.defaultParams.view.mapValues(_.seal.cast[Any]).toMap
+  Expr.ofMapValues(exprs)
+end defaultParamsImpl

tests/run-macros/reflect-defaultParams/Test_2.scala

@@ -0,0 +1,4 @@
+case class Cat(name: String, address: String = "Home", age: Int = 1)
+
+@main def Test =
+  println(defaultParams[Cat])