SI-8403 Fix regression in name binding with imports in templates

Regressed in dbd8457 which changed `Context#make` to automatically
include the imports from the given `Tree` if it was an `Import`
tree, rather than requiring callers to call `makeNewImport`.

However, this turns out to double up the imports for the "inner" namer
of a template that starts with imports. The inner namer has a new
scope, but the same owner and tree as its parent.

This commit detects this case by seeing if the `Import` tree used
to consruct the child context is the same as the parent context.
If that is the case, we don't augment `Context#imports`.

1 files changed, 9 insertions, 0 deletions

diff --git a/test/files/pos/t8403.scala b/test/files/pos/t8403.scala
new file mode 100644
index 0000000000..eea60ed7ff
--- /dev/null
+++ b/test/files/pos/t8403.scala
@@ -0,0 +1,9 @@
+trait Bug {
+  val u: { type Amb } = ???
+  import u._
+ 
+  class Amb { def x = 0 }
+  class C(x: Amb) { // after dbd8457e4, "reference to Amb is ambiguous"
+    x.x
+  }
+}