Improve presentation compilation of annotations

A trio of problems were hampering autocompletion of annotations.

First, given that that annotation is written before the annotated
member, it is very common to end parse incomplete code that has a
floating annotation without an anotatee.

The parser was discarding the annotations (ie, the modifiers) and
emitting an `EmptyTree`.

Second, the presetation compiler was only looking for annotations
in the Modifiers of a member def, but after typechecking annotations
are moved into the symbol.

Third, if an annotation failed to typecheck, it was being discarded
in place of `ErroneousAnnotation`.

This commit:
  - modifies the parser to uses a dummy class- or type-def tree,
    instead of EmptyTree, which can carry the annotations.
  - updates the locator to look in the symbol annotations of the
    modifiers contains no annotations.
  - uses a separate instance of `ErroneousAnnotation` for each
    erroneous annotation, and stores the original tree in its
    `original` tree.

1 files changed, 11 insertions, 0 deletions

diff --git a/test/junit/scala/tools/nsc/interpreter/CompletionTest.scala b/test/junit/scala/tools/nsc/interpreter/CompletionTest.scala
index d00a9bf69a..78ebb7cf9c 100644
--- a/test/junit/scala/tools/nsc/interpreter/CompletionTest.scala
+++ b/test/junit/scala/tools/nsc/interpreter/CompletionTest.scala
@@ -52,6 +52,17 @@ class CompletionTest {
   }
 
   @Test
+  def annotations(): Unit = {
+    val intp = newIMain()
+    val completer = new PresentationCompilerCompleter(intp)
+    checkExact(completer, "def foo[@specialize", " A]")("specialized")
+    checkExact(completer, "def foo[@specialize")("specialized")
+    checkExact(completer, """@deprecatedN""", """ class Foo""")("deprecatedName")
+    checkExact(completer, """@deprecateN""")("deprecatedName")
+    checkExact(completer, """{@deprecateN""")("deprecatedName")
+  }
+
+  @Test
   def incompleteStringInterpolation(): Unit = {
     val intp = newIMain()
     val completer = new PresentationCompilerCompleter(intp)