First draft of the @tostring annotation

src/main/scala/steps/annotation/toString.scala

@@ -0,0 +1,41 @@
+package steps.annotation
+
+import scala.annotation.{experimental, MacroAnnotation}
+import scala.quoted.*
+
+@experimental
+final class toString extends MacroAnnotation:
+  override def transform(using Quotes)(tree: quotes.reflect.Definition): List[quotes.reflect.Definition] = 
+    import quotes.reflect.*
+    val toStringSym = Symbol.requiredMethod("java.lang.Object.toString")
+    tree match
+      case _: ClassDef if toStringSym.overridingSymbol(tree.symbol).exists =>
+        report.warning(s"@toString is not necessary since hashcode is defined in ${tree.symbol}")
+        List(tree)
+      case ClassDef(className, ctr, parents, self, body) =>
+        val cls = tree.symbol
+
+        val fields = body.collect {
+          case vdef: ValDef if vdef.symbol.flags.is(Flags.ParamAccessor) =>
+            Select(This(cls), vdef.symbol).asExpr
+        }
+
+        val toStringOverrideSym = Symbol.newMethod(cls, "toString", toStringSym.info, Flags.Override, Symbol.noSymbol)
+
+        def toStringOverrideDefBody(argss: List[List[Tree]]): Option[Term] =
+          given Quotes = toStringOverrideSym.asQuotes
+          Some(toStringExpr(className, fields).asTerm)
+
+        val toStringDef = DefDef(toStringOverrideSym, toStringOverrideDefBody)
+        List(ClassDef.copy(tree)(className, ctr, parents, self, toStringDef :: body))
+      case _ =>
+        report.errorAndAbort("@toString is only supported in class/object/trait")
+  end transform
+
+  private def toStringExpr(className: String, thisFields: List[Expr[Any]])(using Quotes): Expr[String] =
+    val fieldsSeq = Expr.ofSeq(thisFields)
+    val prefix = Expr(className + "(")
+    '{ $fieldsSeq.mkString($prefix, ", ", ")") }
+  end toStringExpr
+
+end toString