Closes SI-5969.

Assumption that we enter tryTwice when inferring
the right alternative with an empty buffer is
wrong.
In this particular bug it manifested itself on
if/then/else which share the same context and 'else'
branch was simply flushing the buffer with an
error from the 'then' branch.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Infer.scala b/src/compiler/scala/tools/nsc/typechecker/Infer.scala
index 688dcd91ac..e1aabb5469 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Infer.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Infer.scala
@@ -1612,6 +1612,9 @@ trait Infer {
         val saved = context.state
         var fallback = false
         context.setBufferErrors()
+        // Need to test first attempt with an empty buffer.
+        // Otherwise, any previous errors will get lost.
+        val errorsToRestore = context.flushAndReturnBuffer()
         try {
           context.withImplicitsDisabled(infer(false))
           if (context.hasErrors) {
@@ -1625,8 +1628,10 @@ trait Infer {
           case ex: TypeError        => // recoverable cyclic references
             context.restoreState(saved)
             if (!fallback) infer(true) else ()
+        } finally {
+          context.restoreState(saved)
+          context.updateBuffer(errorsToRestore)
         }
-        context.restoreState(saved)
       }
       else infer(true)
     }