Merge pull request scala#2839 from densh/topic/si-7757

SI-7757 disallow constructor annotations on traits

Author: adriaanm

src/compiler/scala/tools/nsc/ast/parser/Parsers.scala

@@ -2693,7 +2693,7 @@ self =>
             syntaxError("traits cannot have type parameters with context bounds `: ...' nor view bounds `<% ...'", skipIt = false)
             classContextBounds = List()
           }
-          val constrAnnots = constructorAnnotations()
+          val constrAnnots = if (!mods.isTrait) constructorAnnotations() else Nil
           val (constrMods, vparamss) =
             if (mods.isTrait) (Modifiers(Flags.TRAIT), List())
             else (accessModifierOpt(), paramClauses(name, classContextBounds, ofCaseClass = mods.isCase))

test/files/neg/t7757a.check

@@ -0,0 +1,4 @@
+t7757a.scala:1: error: ';' expected but '@' found.
+trait Foo @annot
+          ^
+one error found

test/files/neg/t7757a.scala

@@ -0,0 +1 @@
+trait Foo @annot

test/files/neg/t7757b.check

@@ -0,0 +1,4 @@
+t7757b.scala:2: error: expected start of definition
+@annot2
+       ^
+one error found

test/files/neg/t7757b.scala

@@ -0,0 +1,2 @@
+trait Foo2
+@annot2