Address review comments

Author: odersky

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

@@ -371,6 +371,7 @@ object StdNames {
     val Import: N               = "Import"
     val Literal: N              = "Literal"
     val LiteralAnnotArg: N      = "LiteralAnnotArg"
+    val Matchable: N            = "Matchable"
     val MatchCase: N            = "MatchCase"
     val MirroredElemTypes: N    = "MirroredElemTypes"
     val MirroredElemLabels: N   = "MirroredElemLabels"
@@ -387,7 +388,6 @@ object StdNames {
     val Ref: N                  = "Ref"
     val RootPackage: N          = "RootPackage"
     val RootClass: N            = "RootClass"
-    val Matchable: N            = "Matchable"
     val Select: N               = "Select"
     val Shape: N                = "Shape"
     val StringContext: N        = "StringContext"

compiler/src/dotty/tools/dotc/typer/ReTyper.scala

@@ -141,4 +141,4 @@ class ReTyper extends Typer with ReChecking {
   override protected def addAccessorDefs(cls: Symbol, body: List[Tree])(using Context): List[Tree] = body
   override protected def checkEqualityEvidence(tree: tpd.Tree, pt: Type)(using Context): Unit = ()
   override protected def matchingApply(methType: MethodOrPoly, pt: FunProto)(using Context): Boolean = true
-}
+}

library/src/scala/quoted/Quotes.scala

@@ -3411,6 +3411,9 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
       /** The class symbol of core class `scala.Any`. */
       def AnyClass: Symbol
 
+      /** The class symbol of core trait `scala.Matchable` */
+      def MatchableClass: Symbol
+
       /** The class symbol of core class `scala.AnyVal`. */
       def AnyValClass: Symbol
 

tests/neg/extend-matchable.scala

@@ -0,0 +1,23 @@
+trait M0 extends Matchable  // inferred base type is AnyRef
+trait M extends Any, Matchable
+
+class C extends Matchable // OK inferred base type is AnyRef
+class D(x: Int) extends AnyVal, Matchable // OK
+class E extends AnyRef, Matchable // OK
+class F extends Any, Matchable // error: Any does not have a constructor
+
+class C1 extends M // OK inferred base type is AnyRef
+class D1(x: Int) extends AnyVal, M // OK
+class E1 extends AnyRef, M // OK
+class F1 extends Any, M // error: Any does not have a constructor
+
+class C2 extends M0 // OK inferred base type is AnyRef
+class D2(x: Int) extends AnyVal, M0 // error: illegal trait inheritance
+class E2 extends AnyRef, M0 // OK
+class F2 extends Any, M0 // error: Any does not have a constructor // error: illegal trait inheritance
+
+
+
+
+
+

tests/pos/i1044.scala

@@ -1,4 +1,6 @@
 object Test {
   def f[X](x: X) =
+    ???.getClass.getMethods.head.getParameterTypes.mkString(",")
+      // this is the current behavior. But it would also be OK if `???.getClass` fails
     x.getClass.getMethods.head.getParameterTypes.mkString(",")
 }