Support ? as wildcard marker under -Xsource:3

src/compiler/scala/tools/nsc/ast/parser/Parsers.scala

@@ -705,6 +705,10 @@ self =>
     def isRawBar   = isRawIdent && in.name == raw.BAR
     def isRawIdent = in.token == IDENTIFIER
 
+    def isWildcardType =
+      in.token == USCORE ||
+      settings.isScala3 && isRawIdent && in.name == raw.QMARK
+
     def isIdent = in.token == IDENTIFIER || in.token == BACKQUOTED_IDENT
     def isMacro = in.token == IDENTIFIER && in.name == nme.MACROkw
 
@@ -1105,12 +1109,14 @@ self =>
               }
               else
                 atPos(start)(makeSafeTupleType(inParens(types())))
-            case USCORE => wildcardType(in.skipToken())
             case _      =>
-              path(thisOK = false, typeOK = true) match {
-                case r @ SingletonTypeTree(_) => r
-                case r => convertToTypeId(r)
-              }
+              if (isWildcardType)
+                wildcardType(in.skipToken())
+              else
+                path(thisOK = false, typeOK = true) match {
+                  case r @ SingletonTypeTree(_) => r
+                  case r => convertToTypeId(r)
+                }
           })
         }
       }
@@ -1976,18 +1982,16 @@ self =>
       final def functionArgType(): Tree = argType()
       final def argType(): Tree = {
         val start = in.offset
-        in.token match {
-          case USCORE =>
+        if (isWildcardType) {
             in.nextToken()
             if (in.token == SUBTYPE || in.token == SUPERTYPE) wildcardType(start)
             else atPos(start) { Bind(tpnme.WILDCARD, EmptyTree) }
-          case _ =>
-            typ() match {
-              case Ident(name: TypeName) if nme.isVariableName(name) =>
-                atPos(start) { Bind(name, EmptyTree) }
-              case t => t
-            }
-        }
+        } else
+          typ() match {
+            case Ident(name: TypeName) if nme.isVariableName(name) =>
+              atPos(start) { Bind(name, EmptyTree) }
+            case t => t
+          }
       }
 
       /** {{{

src/reflect/scala/reflect/internal/StdNames.scala

@@ -960,6 +960,7 @@ trait StdNames {
       final val PLUS : NameType  = nameType("+")
       final val STAR : NameType  = nameType("*")
       final val TILDE: NameType  = nameType("~")
+      final val QMARK: NameType  = nameType("?")
 
       final val isUnary: Set[Name] = Set(MINUS, PLUS, TILDE, BANG)
     }

test/files/pos/wildcards-future.scala

@@ -0,0 +1,21 @@
+// scalac: -Xsource:3
+//
+object Test {
+  val xs: List[?] = List(1, 2, 3)
+  val ys: Map[? <: AnyRef, ? >: Null] = Map()
+
+  def foo(x: Any) = x match {
+    case x: List[?] => x
+    case _ => x
+  }
+
+  // Only allowed in Scala 3 under -source 3.0-migration
+  type ? = Int
+
+  val xs2: List[`?`] = List(1)
+  val xs3: List[Int] = xs2
+
+  def foo2(x: List[`?`]): List[Int] = x match {
+    case x: List[`?`] => x
+  }
+}