Improve error message on empty catch block

Author: felixmulder

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

@@ -1009,6 +1009,15 @@ object Parsers {
               in.nextToken()
               expr()
             } else EmptyTree
+
+          handler match {
+            case Block(Nil, EmptyTree) => syntaxError(
+              "`catch` block does not contain a valid expression, try adding a case like - `case e: Exception =>` to the block",
+              handler.pos
+            )
+            case _ =>
+          }
+
           val finalizer =
             if (in.token == FINALLY) { accept(FINALLY); expr() }
             else {

tests/neg/emptyCatch.scala

@@ -0,0 +1,3 @@
+object Test {
+  try {} catch {} // error: `catch` block does not contain a valid expression, try adding a case like - `case e: Exception =>` to the block
+}