[flow][debug] Add debug log when we decide that a type is cyclic

Summary:
This is normally logged in flow_js_utils, where we add most errors. However, this one has to exist in context.ml to avoid cyclic modules, and it's missing the log. Logging this can help us debug why something is considered to be cyclic under LTI 2.0

Changelog: [internal]

Reviewed By: panagosg7

Differential Revision: D55775465

fbshipit-source-id: 6587f5b4cd4d57a3161e31cc4120a636b9ee8470

src/typing/context.ml

@@ -1010,6 +1010,18 @@ let find_root_id cx id = Type.Constraint.find_root_id cx.ccx.sig_cx.graph id
 let on_cyclic_tvar_error cx reason =
   let msg = Error_message.(ETrivialRecursiveDefinition (Reason.loc_of_reason reason, reason)) in
   let error = Flow_error.error_of_msg ~trace_reasons:[] ~source_file:cx.file msg in
+  if is_verbose cx then
+    Utils_js.prerr_endlinef
+      "\nCyclic type: %s"
+      (Reason.dump_reason
+         ~strip_root:
+           ( if should_strip_root cx then
+             Some (root cx)
+           else
+             None
+           )
+         reason
+      );
   add_error cx error;
   Type.AnyT.error reason