SI-7345 Produce Context#imports from the context chain

Rather than keeping a List[ImportInfo] around as a field.

This sort of change reduces our bug exposure by structurally
enforcing the invariant that `Context#imports` must mirror
the `outer` chain.

This entails changing a few elements of Contexts from mutable
vars to constructor pararameters, which seems desirable anyway.

We no longer need `makeNewImport`, as `make` now inspects
the provided tree and determines does import specific things
(tracking of used imports / mixin of ImportContext) when
appropriate.

The only wrinkle in this commit is the unfortunate need to pass
`owner = null` in the extends clause of NoContext. I don't see
cleaner way around this.

Applied minor rework to `implicitss` to avoid needlessly re-evaluating
`imports` and `nextOuter`.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Namers.scala b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
index bbb1dbe8d8..e4bfa9d66a 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Namers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
@@ -253,7 +253,7 @@ trait Namers extends MethodSynthesis {
           case DocDef(_, defn)                               => enterSym(defn)
           case tree @ Import(_, _)                           =>
             assignSymbol(tree)
-            returnContext = context.makeNewImport(tree)
+            returnContext = context.make(tree)
           case _ =>
         }
         returnContext