Merge pull request scala#7680 from dotty-staging/fix-#7675

Fix scala#7675: Handle case of lazy patterns with no variables

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1086,7 +1086,7 @@ object desugar {
         if (tupleOptimizable) rhs
         else Match(makeSelector(rhs, MatchCheck.IrrefutablePatDef), caseDef :: Nil)
       vars match {
-        case Nil =>
+        case Nil if !mods.is(Lazy) =>
           matchExpr
         case (named, tpt) :: Nil =>
           derivedValDef(original, named, tpt, matchExpr, mods)

tests/run/i7675.check

@@ -0,0 +1 @@
+Hello, World!

tests/run/i7675.scala

@@ -0,0 +1,4 @@
+object Test extends App {
+  lazy val _ = ??? // throws an exception
+  println("Hello, World!")
+}