Do not crash when typing a closure with unknown type, since it can occur for erroneous input

Author: KacperFKorban

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

@@ -1725,7 +1725,7 @@ object Parsers {
             case arg =>
               arg
           val args1 = args.mapConserve(sanitize)
-          
+
           if in.isArrow || isPureArrow || erasedArgs.contains(true) then
             functionRest(args)
           else

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

@@ -1131,7 +1131,7 @@ class Namer { typer: Typer =>
     private def exportForwarders(exp: Export, pathMethod: Symbol)(using Context): List[tpd.MemberDef] =
       val buf = new mutable.ListBuffer[tpd.MemberDef]
       val Export(expr, selectors) = exp
-      if expr.isEmpty then
+      if expr.isEmpty || (selectors.size == 1 && selectors.exists(s => s.imported.name == nme.ERROR)) then
         report.error(em"Export selector must have prefix and `.`", exp.srcPos)
         return Nil
 

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

@@ -1977,8 +1977,6 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
               // Polymorphic SAMs are not currently supported (#6904).
               EmptyTree
           case tp =>
-            if !tp.isErroneous then
-              throw new java.lang.Error(i"internal error: closing over non-method $tp, pos = ${tree.span}")
             TypeTree(defn.AnyType)
         }
       else typed(tree.tpt)

tests/neg/i20511-1.scala

@@ -0,0 +1,7 @@
+package pakiet
+
+def toppingPrice(size: Int): Double = ???
+
+def crustPrice(crustType: Double): Double = ???
+
+export toppingPrice.apply, crustPrice.unlift // error // error // error

tests/neg/i20511.scala

@@ -0,0 +1,8 @@
+package pakiet
+
+def toppingPrice(size: Int): Double = ???
+
+def crustPrice(crustType: Double): Double = ???
+
+export toppingPrice, crustPrice // error // error
+val i = 1 // error