Fix Splicer.isEscapedVariable (#16838)

Consider that `val macro` expansion in the context can come from an
outer macro that is being expanded (i.e. this is a nested macro). Nested
macro expansion can occur when a macro summons an implicit macro.

Fixes partially #16835

Author: Kordyjan

compiler/src/dotty/tools/dotc/transform/Splicer.scala

@@ -86,7 +86,7 @@ object Splicer {
       }
   }
 
-  /** Checks that no symbol that whas generated within the macro expansion has an out of scope reference */
+  /** Checks that no symbol that was generated within the macro expansion has an out of scope reference */
   def checkEscapedVariables(tree: Tree, expansionOwner: Symbol)(using Context): tree.type =
     new TreeTraverser {
       private[this] var locals = Set.empty[Symbol]
@@ -119,7 +119,10 @@ object Splicer {
         sym.exists && !sym.is(Package)
         && sym.owner.ownersIterator.exists(x =>
           x == expansionOwner || // symbol was generated within this macro expansion
-          isMacroOwner(x) // symbol was generated within another macro expansion
+          { // symbol was generated within another macro expansion
+            isMacroOwner(x) &&
+            !ctx.owner.ownersIterator.contains(x)
+          }
         )
         && !locals.contains(sym) // symbol is not in current scope
     }.traverse(tree)

tests/pos-macros/i16835/Macro_1.scala

@@ -0,0 +1,79 @@
+import scala.quoted.*
+import scala.deriving.Mirror
+
+// derivation code is a slightly modified version of: https://github.com/lampepfl/dotty-macro-examples/blob/main/macroTypeClassDerivation/src/macro.scala
+object Derivation {
+
+  // Typeclass instance gets constructed as part of a macro
+  inline given deriveFullyConstrucedByMacro[A](using Mirror.ProductOf[A]): Show[A] = Derivation.deriveShow[A]
+
+  // Typeclass instance is built inside as part of a method, only the 'show' impl is filled in by a macro
+  inline given derivePartiallyConstructedByMacro[A](using Mirror.ProductOf[A]): Show[A] =
+    new {
+      def show(value: A): String = Derivation.show(value)
+    }
+
+  inline def show[T](value: T): String = ${ showValue('value) }
+
+  inline def deriveShow[T]: Show[T] = ${ deriveCaseClassShow[T] }
+
+  private def deriveCaseClassShow[T](using quotes: Quotes, tpe: Type[T]): Expr[Show[T]] = {
+    import quotes.reflect.*
+    // Getting the case fields of the case class
+    val fields: List[Symbol] = TypeTree.of[T].symbol.caseFields
+
+    '{
+      new Show[T] {
+        override def show(t: T): String =
+          ${ showValue('t) }
+      }
+    }
+  }
+
+  def showValue[T: Type](value: Expr[T])(using Quotes): Expr[String] = {
+    import quotes.reflect.*
+
+    val fields: List[Symbol] = TypeTree.of[T].symbol.caseFields
+
+    val vTerm: Term = value.asTerm
+    val valuesExprs: List[Expr[String]] = fields.map(showField(vTerm, _))
+    val exprOfList: Expr[List[String]] = Expr.ofList(valuesExprs)
+    '{ "{ " + $exprOfList.mkString(", ") + " }" }
+  }
+
+  /** Create a quoted String representation of a given field of the case class */
+  private def showField(using Quotes)(caseClassTerm: quotes.reflect.Term, field: quotes.reflect.Symbol): Expr[String] = {
+    import quotes.reflect.*
+
+    val fieldValDef: ValDef = field.tree.asInstanceOf[ValDef]
+    val fieldTpe: TypeRepr = fieldValDef.tpt.tpe
+    val fieldName: String = fieldValDef.name
+
+    val tcl: Term = lookupShowFor(fieldTpe) // Show[$fieldTpe]
+    val fieldValue: Term = Select(caseClassTerm, field) // v.field
+    val strRepr: Expr[String] = applyShow(tcl, fieldValue).asExprOf[String]
+    '{ ${ Expr(fieldName) } + ": " + $strRepr } // summon[Show[$fieldTpe]].show(v.field)
+  }
+
+  /** Look up the Show[$t] typeclass for a given type t */
+  private def lookupShowFor(using Quotes)(t: quotes.reflect.TypeRepr): quotes.reflect.Term = {
+    import quotes.reflect.*
+    t.asType match {
+      case '[tpe] =>
+        Implicits.search(TypeRepr.of[Show[tpe]]) match {
+          case res: ImplicitSearchSuccess   => res.tree
+          case failure: DivergingImplicit   => report.errorAndAbort(s"Diverving: ${failure.explanation}")
+          case failure: NoMatchingImplicits => report.errorAndAbort(s"NoMatching: ${failure.explanation}")
+          case failure: AmbiguousImplicits  => report.errorAndAbort(s"Ambiguous: ${failure.explanation}")
+          case failure: ImplicitSearchFailure =>
+            report.errorAndAbort(s"catch all: ${failure.explanation}")
+        }
+    }
+  }
+
+  /** Composes the tree: $tcl.show($arg) */
+  private def applyShow(using Quotes)(tcl: quotes.reflect.Term, arg: quotes.reflect.Term): quotes.reflect.Term = {
+    import quotes.reflect.*
+    Apply(Select.unique(tcl, "show"), arg :: Nil)
+  }
+}

tests/pos-macros/i16835/Show_1.scala

@@ -0,0 +1,11 @@
+trait Show[A] {
+  def show(value: A): String
+}
+
+object Show {
+  given identity: Show[String] = a => a
+
+  given int: Show[Int] = _.toString()
+
+  given list[A](using A: Show[A]): Show[List[A]] = _.map(A.show).toString()
+}

tests/pos-macros/i16835/Test_2.scala

@@ -0,0 +1,30 @@
+import scala.deriving.*
+
+object usage {
+  final case class Person(name: String, age: Int, otherNames: List[String], p2: Person2)
+
+  final case class Person2(name: String, age: Int, otherNames: List[String])
+
+  locally {
+    import Derivation.deriveFullyConstrucedByMacro
+    // works for case classes without other nested case classes inside
+    summon[Show[Person2]]
+
+    // also derives instances with nested case classes
+    summon[Show[Person]]
+  }
+
+  locally {
+    import Derivation.derivePartiallyConstructedByMacro
+
+    // works for case classes without other nested case classes inside
+    summon[Show[Person2]]
+
+    // fails for case classes with other nested case classes inside,
+    // note how that error is not a `NonMatching', `Diverging` or `Ambiguous` implicit search error but something else
+    /*
+    catch all: given instance deriveWithConstructionOutsideMacro in object Derivation does not match type io.github.arainko.ducktape.issue_repros.Show[Person2]
+    */
+    summon[Show[Person]]
+  }
+}