Merge pull request #3792 from dotty-staging/fix-#1380

Fix #1380: Add missing part of the message

Author: nicolasstucki

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -193,7 +193,8 @@ object messages {
         else
           ""
 
-      i"missing parameter type for parameter ${param.name}$ofFun, expected = $pt"
+      i"""missing parameter type for parameter ${param.name}$ofFun, expected = $pt
+         |The argument types of an anonymous function must be fully known. (SLS 8.5)"""
     }
 
     val explanation =

compiler/test-resources/repl/errorThenValid

@@ -1,6 +1,7 @@
 scala> val xs = scala.collection.mutable.ListBuffer[Int]
 1 | val xs = scala.collection.mutable.ListBuffer[Int]
   |          ^
-  |          missing parameter type for parameter elems, expected = ?
+  |missing parameter type for parameter elems, expected = ?
+  |The argument types of an anonymous function must be fully known. (SLS 8.5)
 scala> val xs = scala.collection.mutable.ListBuffer[Int]()
 val xs: scala.collection.mutable.ListBuffer[Int] = ListBuffer()