SI-10207 Error before update conversion

Gaze deeper for errors before committing to conversion
of assignment to update. The error buried in the transformed
tree escapes notice of retypechecking and leaks to backend.

2 files changed, 20 insertions, 0 deletions

diff --git a/test/files/neg/t10207.check b/test/files/neg/t10207.check
new file mode 100755
index 0000000000..3330db44a5
--- /dev/null
+++ b/test/files/neg/t10207.check
@@ -0,0 +1,4 @@
+t10207.scala:14: error: too many arguments (2) for method apply: (key: Int)scala.collection.mutable.ArrayBuffer[String] in trait MapLike
+  m(1, (_ => empty)) ++= AB("eins", "uno")
+          ^
+one error found
diff --git a/test/files/neg/t10207.scala b/test/files/neg/t10207.scala
new file mode 100644
index 0000000000..2dfc5d75c9
--- /dev/null
+++ b/test/files/neg/t10207.scala
@@ -0,0 +1,16 @@
+
+// Was:
+// warning: an unexpected type representation reached the compiler backend
+// Now:
+// error: too many arguments (2) for method apply: (key: Int)scala.collection.mutable.ArrayBuffer[String] in trait MapLike
+
+trait Test {
+  import collection.mutable.{Map=>MMap, ArrayBuffer=>AB}
+
+  val m = MMap((1 -> AB("one")))
+
+  val empty = AB[String]()
+
+  m(1, (_ => empty)) ++= AB("eins", "uno")
+}
+