SI-7345 Prefer using a throwaway silent context over buffer flushing.

When we are using a throwaway silent context, we can just let it drift out of
scope and over the horizon, rather than ceremoniously flushing its buffers
on completion.

 - Applied to Scaladoc.
 - Applied to Infer#isApplicableSafe. Less manual error buffer management
   affords greater opportunity to cleanly express the logic.
 - Applied to `typerReportAnyContextErrors`.

The reasoning for the last case is as follows:

 - There were only two callers to `typerReportAnyContextErrors`, and
   they both passed in as `c` a child context of `context`.
 - That child context must share the error reporting mode and buffer
   with `context`.
 - Therefore, extracting an error from `c` and issuing it into `context`
   is a no-op. Because the error buffer is Set, it was harmless.

This part will probably textually conflict with the same change made in
SI-7319, but the end results are identical.

1 files changed, 6 insertions, 4 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
index 4b9d3fda01..4fc9cde070 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
@@ -261,11 +261,13 @@ trait Contexts { self: Analyzer =>
       reportBuffer.clearAllErrors()
       current
     }
-    /** Return and clear all warnings from the report buffer */
-    def flushAndReturnWarningsBuffer(): immutable.Seq[(Position, String)] = {
-      val current = reportBuffer.warnings
+
+    /** Issue and clear all warnings from the report buffer */
+    def flushAndIssueWarnings() {
+      reportBuffer.warnings foreach {
+        case (pos, msg) => unit.warning(pos, msg)
+      }
       reportBuffer.clearAllWarnings()
-      current
     }
 
     //