warn if search excluded unofficial taps

warn if description search exludes any formulae/casks because --eval-all
flag wasn't set

Library/Homebrew/search.rb

@@ -28,6 +28,11 @@ def self.search_descriptions(string_or_regex, args, search_type: :desc)
             Descriptions.search(string_or_regex, search_type, cache_store, eval_all).print
           end
         else
+          unofficial = Tap.all.sum { |tap| tap.official? ? 0 : tap.formula_files.size }
+          if unofficial.positive?
+            opoo "#{unofficial} additional formula(e) in third party repositories were not searched.\n" \
+                 "To search all formulae repeat this search with the flag `--eval-all`."
+          end
           descriptions = Homebrew::API::Formula.all_formulae.transform_values { |data| data["desc"] }
           Descriptions.search(string_or_regex, search_type, descriptions, eval_all, cache_store_hash: true).print
         end
@@ -43,6 +48,11 @@ def self.search_descriptions(string_or_regex, args, search_type: :desc)
           Descriptions.search(string_or_regex, search_type, cache_store, eval_all).print
         end
       else
+        unofficial = Tap.all.sum { |tap| tap.official? ? 0 : tap.cask_files.size }
+        if unofficial.positive?
+          opoo "#{unofficial} additional cask(s) in third party repositories were not searched.\n" \
+               "To search all casks repeat this search with the flag `--eval-all`."
+        end
         descriptions = Homebrew::API::Cask.all_casks.transform_values { |data| data["desc"] }
         Descriptions.search(string_or_regex, search_type, descriptions, eval_all, cache_store_hash: true).print
       end