Put up a fix for challenges whose requirements were deleted (CTFd#1861)

* Works on CTFd#1860 
* Don't consider deleted challenges when evaluating challenge prereqs

CTFd/api/v1/challenges.py

@@ -232,12 +232,17 @@ def get(self, query_args):
         # will be JSONified back to the client
         response = []
         tag_schema = TagSchema(view="user", many=True)
+
+        # Gather all challenge IDs so that we can determine invalid challenge prereqs
+        all_challenge_ids = {
+            c.id for c in Challenges.query.with_entities(Challenges.id).all()
+        }
         for challenge in chal_q:
             if challenge.requirements:
                 requirements = challenge.requirements.get("prerequisites", [])
                 anonymize = challenge.requirements.get("anonymize")
-                prereqs = set(requirements)
-                if user_solves >= prereqs:
+                prereqs = set(requirements).intersection(all_challenge_ids)
+                if user_solves >= prereqs or admin_view:
                     pass
                 else:
                     if anonymize:
@@ -365,6 +370,10 @@ def get(self, challenge_id):
         if chal.requirements:
             requirements = chal.requirements.get("prerequisites", [])
             anonymize = chal.requirements.get("anonymize")
+            # Gather all challenge IDs so that we can determine invalid challenge prereqs
+            all_challenge_ids = {
+                c.id for c in Challenges.query.with_entities(Challenges.id).all()
+            }
             if challenges_visible():
                 user = get_current_user()
                 if user:
@@ -378,7 +387,7 @@ def get(self, challenge_id):
                     # We need to handle the case where a user is viewing challenges anonymously
                     solve_ids = []
                 solve_ids = {value for value, in solve_ids}
-                prereqs = set(requirements)
+                prereqs = set(requirements).intersection(all_challenge_ids)
                 if solve_ids >= prereqs or is_admin():
                     pass
                 else:
@@ -603,7 +612,11 @@ def post(self):
                 .all()
             )
             solve_ids = {solve_id for solve_id, in solve_ids}
-            prereqs = set(requirements)
+            # Gather all challenge IDs so that we can determine invalid challenge prereqs
+            all_challenge_ids = {
+                c.id for c in Challenges.query.with_entities(Challenges.id).all()
+            }
+            prereqs = set(requirements).intersection(all_challenge_ids)
             if solve_ids >= prereqs:
                 pass
             else:

CTFd/themes/admin/assets/js/components/requirements/Requirements.vue

@@ -12,7 +12,7 @@
           v-for="requirement in requirements.prerequisites"
           :key="requirement"
         >
-          <td>{{ getChallengeById(requirement).name }}</td>
+          <td>{{ getChallengeNameById(requirement) }}</td>
           <td>
             <i
               role="button"
@@ -99,8 +99,11 @@ export default {
           }
         });
     },
-    getChallengeById: function(challenge_id) {
-      return this.challenges.find(challenge => challenge.id === challenge_id);
+    getChallengeNameById: function(challenge_id) {
+      let challenge = this.challenges.find(
+        challenge => challenge.id === challenge_id
+      );
+      return challenge ? challenge.name : "";
     },
     loadRequirements: function() {
       CTFd.fetch(