From 8544c301609d528263e5cd0867d98e8c62565792 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Wed, 6 Jan 2021 15:51:51 +0100
Subject: [PATCH] Avoid NoDenotation.owner in some situations

Fixes #9328
---
 .../tools/dotc/core/SymDenotations.scala      |  4 ++--
 .../dotty/tools/dotc/typer/Implicits.scala    | 17 ++++++++-------
 tests/neg/i9328.scala                         | 21 +++++++++++++++++++
 3 files changed, 32 insertions(+), 10 deletions(-)
 create mode 100644 tests/neg/i9328.scala

diff --git a/compiler/src/dotty/tools/dotc/core/SymDenotations.scala b/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
index 05eb9c435fb7..cad0d282bc16 100644
--- a/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
+++ b/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
@@ -1393,10 +1393,10 @@ object SymDenotations {
     def thisType(using Context): Type = NoPrefix
 
     def typeRef(using Context): TypeRef =
-      TypeRef(owner.thisType, symbol)
+      TypeRef(maybeOwner.thisType, symbol)
 
     def termRef(using Context): TermRef =
-      TermRef(owner.thisType, symbol)
+      TermRef(maybeOwner.thisType, symbol)
 
     /** The typeRef applied to its own type parameters */
     def appliedRef(using Context): Type =
diff --git a/compiler/src/dotty/tools/dotc/typer/Implicits.scala b/compiler/src/dotty/tools/dotc/typer/Implicits.scala
index 761d550afc96..063d92221166 100644
--- a/compiler/src/dotty/tools/dotc/typer/Implicits.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Implicits.scala
@@ -1657,14 +1657,15 @@ sealed class TermRefSet(using Context):
 
   def += (ref: TermRef): Unit =
     val pre = ref.prefix
-    val sym = ref.symbol.asTerm
-    elems.get(sym) match
-      case null =>
-        elems.put(sym, pre)
-      case prefix: Type =>
-        if !(prefix =:= pre) then elems.put(sym, pre :: prefix :: Nil)
-      case prefixes: List[Type] =>
-        if !prefixes.exists(_ =:= pre) then elems.put(sym, pre :: prefixes)
+    if ref.symbol.exists then
+      val sym = ref.symbol.asTerm
+      elems.get(sym) match
+        case null =>
+          elems.put(sym, pre)
+        case prefix: Type =>
+          if !(prefix =:= pre) then elems.put(sym, pre :: prefix :: Nil)
+        case prefixes: List[Type] =>
+          if !prefixes.exists(_ =:= pre) then elems.put(sym, pre :: prefixes)
 
   def ++= (that: TermRefSet): Unit =
     if !that.isEmpty then that.foreach(+=)
diff --git a/tests/neg/i9328.scala b/tests/neg/i9328.scala
new file mode 100644
index 000000000000..c4b5e0cf19e2
--- /dev/null
+++ b/tests/neg/i9328.scala
@@ -0,0 +1,21 @@
+// fuzz test to avoid NoSymbol.owner
+type Id[T] = T match {
+  case _ => T
+}
+
+class Foo2[T <: Id[T]] // error // error
+
+object Foo { // error
+  object Foo { }
+  Foo { }
+}
+implicit class Foo(a: Float)  // error
+case class Foo()
+
+case class Bar(
+} { ;  // error
+object Bar { // error
+  class Foo(a: Int) extends AnyVal
+  Foo()
+}
+type Bar // error
\ No newline at end of file