Avoid infinite recursions.

caniusepython3/dependencies.py

@@ -75,6 +75,7 @@ def blocking_dependencies(projects, py3_projects):
     """
     log = logging.getLogger('ciu')
     check = []
+    checked = set()
     for project in projects:
         dist = distlib.locators.locate(project)
         if dist is None:
@@ -90,6 +91,7 @@ def blocking_dependencies(projects, py3_projects):
         while len(check) > 0:
             new_check = []
             for parent, deps in zip(check, executor.map(dependencies, check)):
+                checked.add(parent)
                 if deps is None:
                     # Can't find any results for a project, so ignore it so as
                     # to not accidentally consider indefinitely that a project
@@ -100,6 +102,9 @@ def blocking_dependencies(projects, py3_projects):
                     if dep in py3_projects:
                         continue
                     reasons[dep] = parent
-                    new_check.append(dep)
+                    if dep not in checked:
+                        new_check.append(dep)
+                    else:
+                        log.info('{0} already checked'.format(dep))
             check = new_check
     return reasons_to_paths(reasons)