Check patvar names

Author: som-snytt

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -3425,6 +3425,9 @@ object Parsers {
           p = atSpan(startOffset(t), in.offset) { TypeApply(p, typeArgs(namedOK = false, wildOK = false)) }
         if (in.token == LPAREN)
           p = atSpan(startOffset(t), in.offset) { Apply(p, argumentPatterns()) }
+        p match
+        case nt: NameTree if isVarPattern(nt) => checkName(nt)
+        case _ =>
         p
 
     /** Patterns          ::=  Pattern [`,' Pattern]

tests/neg/i18234.scala

@@ -162,3 +162,8 @@ package BadPackageEnd$ : // error
 
 class BadConstructor:
   def `<init>`() = () // error // error
+
+def patvar[A](x: Option[A]) =
+  x match
+  case Some(funky$thing) => true // error
+  case _ => false

tests/pos/i18234.scala

@@ -1,3 +1,9 @@
+//> using options -Werror
 
 class `C$Z`:
   override def toString = "C$Z"
+
+  def patvar[A](x: Option[A]) =
+    x match
+    case Some(`funky$thing` @ _) => true
+    case _ => false