refactor: allow vocabularies to expand as well - not sure if thats useful

include/jvalidate/detail/vocabulary.h

@@ -18,7 +18,7 @@ public:
 private:
   schema::Version version_;
   std::unordered_map<std::string_view, MakeConstraint> make_;
-  std::unordered_set<std::string_view> special_keywords_;
+  std::unordered_set<std::string_view> permitted_;
 
   // TODO(samjaffe): Migrate this back to constraintsfactory
   std::unordered_set<std::string_view> keywords_{"$defs",
@@ -49,14 +49,17 @@ private:
 public:
   Vocabulary() = default;
   Vocabulary(schema::Version version, std::unordered_map<std::string_view, MakeConstraint> make)
-      : version_(version), make_(std::move(make)) {}
+      : version_(version), make_(std::move(make)) {
+    for (auto const & [keyword, _] : make_) {
+      permitted_.emplace(keyword);
+    }
+  }
 
   void restrict(std::unordered_set<std::string> const & permitted_keywords) & {
-    for (auto it = make_.begin(); it != make_.end();) {
-      if (permitted_keywords.contains(std::string(it->first))) {
-        ++it;
-      } else {
-        it = make_.erase(it);
+    permitted_.clear();
+    for (auto const & [keyword, _] : make_) {
+      if (permitted_keywords.contains(std::string(keyword))) {
+        permitted_.insert(keyword);
       }
     }
   }
@@ -68,7 +71,7 @@ public:
    * I expect to resolve a constraint out of it.
    */
   bool is_keyword(std::string_view word) const {
-    return make_.contains(word) && keywords_.contains(word);
+    return permitted_.contains(word) && make_.contains(word) && keywords_.contains(word);
   }
 
   /**
@@ -79,7 +82,9 @@ public:
     return is_keyword(word) && property_keywords_.contains(word);
   }
 
-  bool is_constraint(std::string_view word) const { return make_.contains(word) && make_.at(word); }
+  bool is_constraint(std::string_view word) const {
+    return permitted_.contains(word) && make_.contains(word) && make_.at(word);
+  }
 
   auto constraint(std::string_view word, ParserContext<A> const & context) const {
     return std::make_pair(is_constraint(word) ? make_.at(word)(context) : nullptr,