search: use a queue to collect errors

The threading in the tap search code makes handling errors difficult. If
an API-related error is raised in one thread, it is likely to be raised
in each of the rest as well. This results in duplicated error messages,
which is ugly and bad UX.

This patch adds a synchronized queue to collect these exceptions. The
first one added to the queue is re-raised after all operations are
complete.

It's not ideal, but it's minimally invasive and I don't have the energy
or time to do a rewrite.

Library/Homebrew/cmd/search.rb

@@ -1,9 +1,12 @@
 require 'formula'
 require 'blacklist'
 require 'utils'
+require 'thread'
 
 module Homebrew extend self
 
+  SEARCH_ERROR_QUEUE = Queue.new
+
   # A regular expession to capture the username (one or more char but no `/`,
   # which has to be escaped like `\/`), repository, followed by an optional `/`
   # and an optional query.
@@ -64,10 +67,12 @@ module Homebrew extend self
         begin
           GitHub.print_pull_requests_matching(query)
         rescue GitHub::Error => e
-          opoo e.message
+          SEARCH_ERROR_QUEUE << e
         end
       end
     end
+
+    raise SEARCH_ERROR_QUEUE.pop unless SEARCH_ERROR_QUEUE.empty?
   end
 
   SEARCHABLE_TAPS = [
@@ -115,12 +120,14 @@ module Homebrew extend self
         end
       end
     end
-    results
-  rescue GitHub::RateLimitExceededError => e
-    []
-  rescue GitHub::Error => e
+  rescue GitHub::HTTPNotFoundError => e
     opoo "Failed to search tap: #{user}/#{repo}. Please run `brew update`"
     []
+  rescue GitHub::Error => e
+    SEARCH_ERROR_QUEUE << e
+    []
+  else
+    results
   end
 
   def search_formulae rx