SI-8407 "symbol not found" in Scaladoc use cases: warning only

The refactoring in aedec1980 mistakenly used the non-silent
typer to typecheck the use cases. It temptingly had the desired
type (`ScalaDocAnalyzer`), but sadly the wrong properties (it will
report errors, rather than buffer.)

This meant that "symbol not found" errors in use cases would prevent
Scaladoc generation.

This commit introduces a little downcast on the silent typer.
A more principled approach would be to go through the rigmarole
of the virtual class pattern for `Analzyer.Typer`, but that will
have to remain work for another day.

2 files changed, 24 insertions, 0 deletions

diff --git a/test/scaladoc/run/t8407.check b/test/scaladoc/run/t8407.check
new file mode 100644
index 0000000000..06c860b3eb
--- /dev/null
+++ b/test/scaladoc/run/t8407.check
@@ -0,0 +1,4 @@
+newSource:4: warning: not found: type $NotFound
+   *  @usecase def zipWithIndex: $NotFound
+               ^
+Done.
diff --git a/test/scaladoc/run/t8407.scala b/test/scaladoc/run/t8407.scala
new file mode 100644
index 0000000000..2df9f4f1ac
--- /dev/null
+++ b/test/scaladoc/run/t8407.scala
@@ -0,0 +1,20 @@
+import scala.tools.nsc.doc.model._
+import scala.tools.partest.ScaladocModelTest
+
+object Test extends ScaladocModelTest {
+  override def code = """
+class C {
+  /**
+   *  @usecase def zipWithIndex: $NotFound
+   *
+   */
+  def zipWithIndex: Int = ???
+}
+  """
+
+  def scaladocSettings = ""
+
+  def testModel(root: Package) = {
+    // just testing that it doesn't error out.
+  }
+}