Assert that symbols created using reflect API have correct privateWithin symbols

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

@@ -170,7 +170,7 @@ object Symbols {
       asInstanceOf[TermSymbol]
     }
     final def asType(using Context): TypeSymbol = {
-      assert(isType, s"isType called on not-a-Type $this");
+      assert(isType, s"asType called on not-a-Type $this");
       asInstanceOf[TypeSymbol]
     }
 

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

@@ -2504,6 +2504,7 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
 
       def newModule(owner: Symbol, name: String, modFlags: Flags, clsFlags: Flags, parents: List[TypeRepr], decls: Symbol => List[Symbol], privateWithin: Symbol): Symbol =
         assert(parents.nonEmpty && !parents.head.typeSymbol.is(dotc.core.Flags.Trait), "First parent must be a class")
+        assert(!privateWithin.exists || privateWithin.isType, "privateWithin must be a type symbol or `Symbol.noSymbol`")
         val mod = dotc.core.Symbols.newNormalizedModuleSymbol(
           owner,
           name.toTermName,
@@ -2520,8 +2521,10 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
       def newMethod(owner: Symbol, name: String, tpe: TypeRepr): Symbol =
         newMethod(owner, name, tpe, Flags.EmptyFlags, noSymbol)
       def newMethod(owner: Symbol, name: String, tpe: TypeRepr, flags: Flags, privateWithin: Symbol): Symbol =
+        assert(!privateWithin.exists || privateWithin.isType, "privateWithin must be a type symbol or `Symbol.noSymbol`")
         dotc.core.Symbols.newSymbol(owner, name.toTermName, flags | dotc.core.Flags.Method, tpe, privateWithin)
       def newVal(owner: Symbol, name: String, tpe: TypeRepr, flags: Flags, privateWithin: Symbol): Symbol =
+        assert(!privateWithin.exists || privateWithin.isType, "privateWithin must be a type symbol or `Symbol.noSymbol`")
         dotc.core.Symbols.newSymbol(owner, name.toTermName, flags, tpe, privateWithin)
       def newBind(owner: Symbol, name: String, flags: Flags, tpe: TypeRepr): Symbol =
         dotc.core.Symbols.newSymbol(owner, name.toTermName, flags | Case, tpe)

tests/neg/i17351/Macro_1.scala

@@ -0,0 +1,16 @@
+import scala.quoted.*
+
+inline def gen: Unit = ${ genImpl }
+
+def genImpl(using Quotes): Expr[Unit] = {
+  import quotes.reflect.*
+
+  val valDefSymbol = Symbol.newVal(Symbol.spliceOwner, "bar", TypeRepr.of[Unit], Flags.EmptyFlags, Symbol.spliceOwner)
+
+  val valDef = ValDef(valDefSymbol, Some('{ () }.asTerm))
+
+  Block(
+    List(valDef),
+    '{ () }.asTerm
+  ).asExprOf[Unit]
+}

tests/neg/i17351/Test_2.scala

@@ -0,0 +1 @@
+val foo = gen // error