Use context for buffering errors that cannot/shouldn't be reported in the given moment (instead of throwing type errors). This avoids previous problems where we were creating fake error trees in some incorrect places like in type completers in Namers etc. Implicits relied heavily on type errors being thrown but performance should stay the same due to some explicit checks/returns.

Some of the problems involved how ambiguous error messages were collected/reported because it was very random (similarly for divergent implicits). This should be more explicit now. Reduced the number of unnecessary cyclic references being thrown (apart from those in Symbols/Types which don't have a context and need to stay for now as is).

Review by @paulp, @odersky.

1 files changed, 3 insertions, 3 deletions

diff --git a/test/files/neg/t2918.check b/test/files/neg/t2918.check
index 263beab518..aae3045e8a 100644
--- a/test/files/neg/t2918.check
+++ b/test/files/neg/t2918.check
@@ -1,10 +1,10 @@
 t2918.scala:2: error: illegal cyclic reference involving type A
-  def g[X, A[X] <: A[X]](x: A[X]) = x 
+  def g[X, A[X] <: A[X]](x: A[X]) = x
                                     ^
 t2918.scala:2: error: cyclic aliasing or subtyping involving type A
-  def g[X, A[X] <: A[X]](x: A[X]) = x 
+  def g[X, A[X] <: A[X]](x: A[X]) = x
            ^
 t2918.scala:2: error: A does not take type parameters
-  def g[X, A[X] <: A[X]](x: A[X]) = x 
+  def g[X, A[X] <: A[X]](x: A[X]) = x
                             ^
 three errors found