SI-6923 Context now buffers warnings as well as errors

Code that was silently typed would not report warnings, even if it
returned a successful result.

This appeared in the following code which didn't show warnings even
with -Ywarn-adapted-args:

    def foo(a: Any) = a; foo(1, 2)

While the following would show the expected warning:

    def foo[A](a: Any) = a; foo(1, 2)

1 files changed, 9 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 9d390476db..8722aa3666 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -728,7 +728,15 @@ trait Typers extends Modes with Adaptations with Tags {
           if (context1.hasErrors) {
             stopStats()
             SilentTypeError(context1.errBuffer.head)
-          } else SilentResultValue(result)
+          } else {
+            // If we have a successful result, emit any warnings it created.
+            if (context1.hasWarnings) {
+              context1.flushAndReturnWarningsBuffer() foreach {
+                case (pos, msg) => unit.warning(pos, msg)
+              }
+            }
+            SilentResultValue(result)
+          }
         } else {
           assert(context.bufferErrors || isPastTyper, "silent mode is not available past typer")
           withSavedContext(context){