A band-aid solution for SI-5803.

Since ae5ff662, resetAttrs duplicates trees, which doesn't preserve ApplyConstructor.
My attempt to modify TreeCopier to do so proved trickier than expected.

In any case, ApplyConstructor is not long for this world, and is only used in tree printing
to distinguish `new X` from regular Apply trees, so this should suffice pending full surgery.

3 files changed, 10 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/ast/Trees.scala b/src/compiler/scala/tools/nsc/ast/Trees.scala
index 4c509778e9..1b8fe9a91a 100644
--- a/src/compiler/scala/tools/nsc/ast/Trees.scala
+++ b/src/compiler/scala/tools/nsc/ast/Trees.scala
@@ -362,7 +362,8 @@ trait Trees extends reflect.internal.Trees { self: Global =>
       }
 
       val x1 = new Transformer().transform(x)
-      assert(x.getClass isInstance x1, x1.getClass)
+      // The loose invariant is a temporary workaround for SI-5803
+      assert(x.getClass.isInstance(x1) || (x.isInstanceOf[ApplyConstructor] && x1.isInstanceOf[Apply]), (x.getClass, x1.getClass))
       x1.asInstanceOf[T]
     }
   }
diff --git a/test/files/neg/t5803.check b/test/files/neg/t5803.check
new file mode 100644
index 0000000000..6a2de2e1df
--- /dev/null
+++ b/test/files/neg/t5803.check
@@ -0,0 +1,4 @@
+t5803.scala:3: error: could not find implicit value for parameter ev: Nothing
+  new Foo(): String
+  ^
+one error found
diff --git a/test/files/neg/t5803.scala b/test/files/neg/t5803.scala
new file mode 100644
index 0000000000..f818272f86
--- /dev/null
+++ b/test/files/neg/t5803.scala
@@ -0,0 +1,4 @@
+object Test {
+  class Foo()(implicit ev: Nothing)
+  new Foo(): String
+}