Fix #7986: Propagate cyclic reference errors for extension methods

Propagate cyclic reference errors when searching extension methods

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -3056,6 +3056,7 @@ class Typer extends Namer
                 case _ => EmptyTree
               }
             catch {
+              case ex: CyclicReference => throw ex
               case ex: TypeError => errorTree(tree, ex, tree.sourcePos)
             }
           val nestedCtx = ctx.fresh.setNewTyperState()

tests/neg/i7986.scala

@@ -0,0 +1,3 @@
+case class Project(name: String)
+def (name: String) dependencies = ???
+def (project: Project) dependencies = project.name.dependencies // error: needs return type

tests/pos/i7986.scala

@@ -0,0 +1,3 @@
+case class Project(name: String)
+def (name: String) dependencies: String = ???
+def (project: Project) dependencies: String = project.name.dependencies