From cc0041b7c22166cd6acc6a91abfdd76ebe99c20e Mon Sep 17 00:00:00 2001
From: odersky <odersky@gmail.com>
Date: Sat, 3 Feb 2024 16:41:30 +0100
Subject: [PATCH] Refine handling of StaleSymbol type errors

Regular StaleSymbol can be caught and masked in some situations. Stale symbol
type errors need to allow the same.

Fixes #19604

[Cherry-picked fbffe7b3be0dada9cf35e2d5aa5779889ce5fb61]
---
 .../dotty/tools/dotc/core/Denotations.scala   | 20 +++++++---
 tests/pos/i19604/ZSet.scala                   | 11 ++++++
 tests/pos/i19604/core.scala                   | 37 +++++++++++++++++++
 tests/pos/i19604/macro.scala                  |  8 ++++
 tests/pos/i19604/prelude.scala                |  8 ++++
 5 files changed, 79 insertions(+), 5 deletions(-)
 create mode 100644 tests/pos/i19604/ZSet.scala
 create mode 100644 tests/pos/i19604/core.scala
 create mode 100644 tests/pos/i19604/macro.scala
 create mode 100644 tests/pos/i19604/prelude.scala

diff --git a/compiler/src/dotty/tools/dotc/core/Denotations.scala b/compiler/src/dotty/tools/dotc/core/Denotations.scala
index f568117c72a0..6170bc97d3df 100644
--- a/compiler/src/dotty/tools/dotc/core/Denotations.scala
+++ b/compiler/src/dotty/tools/dotc/core/Denotations.scala
@@ -22,6 +22,7 @@ import config.Config
 import config.Printers.overload
 import util.common.*
 import typer.ProtoTypes.NoViewsAllowed
+import reporting.Message
 import collection.mutable.ListBuffer
 
 /** Denotations represent the meaning of symbols and named types.
@@ -945,10 +946,9 @@ object Denotations {
     }
 
     def staleSymbolError(using Context): Nothing =
-      if symbol.isPackageObject && ctx.run != null && ctx.run.nn.isCompilingSuspended then
-        throw TypeError(em"Cyclic macro dependency; macro refers to a toplevel symbol in ${symbol.source} from which the macro is called")
-      else
-        throw new StaleSymbol(staleSymbolMsg)
+      if symbol.isPackageObject && ctx.run != null && ctx.run.nn.isCompilingSuspended
+      then throw StaleSymbolTypeError(symbol)
+      else throw StaleSymbolException(staleSymbolMsg)
 
     def staleSymbolMsg(using Context): String = {
       def ownerMsg = this match {
@@ -1356,9 +1356,19 @@ object Denotations {
     else
       NoSymbol
 
+  trait StaleSymbol extends Exception
+
   /** An exception for accessing symbols that are no longer valid in current run */
-  class StaleSymbol(msg: => String) extends Exception {
+  class StaleSymbolException(msg: => String) extends Exception, StaleSymbol {
     util.Stats.record("stale symbol")
     override def getMessage(): String = msg
   }
+
+  /** An exception that is at the same type a StaleSymbol and a TypeError.
+   *  Sine it is a TypeError it can be reported as a nroaml error instead of crashing
+   *  the compiler.
+   */
+  class StaleSymbolTypeError(symbol: Symbol)(using Context) extends TypeError, StaleSymbol:
+    def toMessage(using Context) =
+      em"Cyclic macro dependency; macro refers to a toplevel symbol in ${symbol.source} from which the macro is called"
 }
diff --git a/tests/pos/i19604/ZSet.scala b/tests/pos/i19604/ZSet.scala
new file mode 100644
index 000000000000..b27c6a939f6c
--- /dev/null
+++ b/tests/pos/i19604/ZSet.scala
@@ -0,0 +1,11 @@
+// ZSet.scala
+// moving it to core.scala would lead to Recursion limit exceeded: find-member prelude.ZSetSyntax
+package prelude
+
+import prelude.newtypes._
+
+class ZSet[+A, +B]
+object ZSet
+trait ZSetSyntax {
+  implicit final class ZSetMapOps[+A](self: Map[A, Natural])
+}
\ No newline at end of file
diff --git a/tests/pos/i19604/core.scala b/tests/pos/i19604/core.scala
new file mode 100644
index 000000000000..26b56fb0f8f2
--- /dev/null
+++ b/tests/pos/i19604/core.scala
@@ -0,0 +1,37 @@
+// core.scala
+package prelude
+
+sealed trait Assertion[-A]
+object Assertion:
+  def greaterThanOrEqualTo[A](value: A): Assertion[A] = ???
+
+sealed trait AssertionError
+
+abstract class NewtypeCustom[A] {
+  type Type
+  protected inline def validateInline(inline value: A): Unit
+
+  inline def apply(inline a1: A): Type = {
+    validateInline(a1)
+    a1.asInstanceOf[Type]
+  }
+}
+abstract class Newtype[A] extends NewtypeCustom[A] {
+  def assertion: Assertion[A] = ???
+  protected inline def validateInline(inline value: A): Unit = ${
+    Macros.validateInlineImpl[A]('assertion, 'value)
+  }
+}
+
+abstract class Subtype[A] extends Newtype[A] {
+  type Type <: A
+}
+
+
+package object newtypes {
+  type Natural = Natural.Type
+  object Natural extends Subtype[Int] {
+    override inline def assertion = Assertion.greaterThanOrEqualTo(0)
+    val one: Natural =  Natural(1) // triggers macro
+  }
+}
\ No newline at end of file
diff --git a/tests/pos/i19604/macro.scala b/tests/pos/i19604/macro.scala
new file mode 100644
index 000000000000..fa1faba10512
--- /dev/null
+++ b/tests/pos/i19604/macro.scala
@@ -0,0 +1,8 @@
+// macro.scala
+package prelude
+import scala.quoted.*
+
+object Macros {
+  def validateInlineImpl[A: Type](assertionExpr: Expr[Assertion[A]], a: Expr[A])(using Quotes): Expr[Unit] =
+    '{ () }
+}
diff --git a/tests/pos/i19604/prelude.scala b/tests/pos/i19604/prelude.scala
new file mode 100644
index 000000000000..3a8292d3d2ec
--- /dev/null
+++ b/tests/pos/i19604/prelude.scala
@@ -0,0 +1,8 @@
+// prelude.scala
+
+import prelude.newtypes.Natural
+
+package object prelude extends ZSetSyntax {
+  type MultiSet[+A] = ZSet[A, Natural]
+  val MultiSet: ZSet.type = ZSet
+}
\ No newline at end of file