Set the return_value from the initialize block in the DatabaseCache.

Library/Homebrew/cache_store.rb

@@ -12,6 +12,9 @@ class DatabaseCache
   #   https://docs.oracle.com/cd/E17276_01/html/api_reference/C/envopen.html
   DATABASE_MODE = 0664
 
+  # Returned value from `initialize` block
+  attr_reader :return_value
+
   # Opens and yields a database in read/write mode. Closes the database after use
   #
   # @yield  [DBM] db
@@ -19,7 +22,7 @@ class DatabaseCache
   def initialize(name)
     # DBM::WRCREAT: Creates the database if it does not already exist
     @db = DBM.open("#{HOMEBREW_CACHE}/#{name}.db", DATABASE_MODE, DBM::WRCREAT)
-    yield(@db)
+    @return_value = yield(@db)
     @db.close
   end
 end

Library/Homebrew/formula.rb

@@ -1527,11 +1527,13 @@ class Formula
     keg = opt_or_installed_prefix_keg
     return [] unless keg
 
-    DatabaseCache.new(:linkage) do |database_cache|
+    cache = DatabaseCache.new(:linkage) do |database_cache|
       use_cache = !ENV["HOMEBREW_LINKAGE_CACHE"].nil?
       linkage_checker = LinkageChecker.new(keg, database_cache, use_cache, self)
-      break linkage_checker.undeclared_deps.map { |n| Dependency.new(n) }
+      linkage_checker.undeclared_deps.map { |n| Dependency.new(n) }
     end
+
+    cache.return_value
   end
 
   # Returns a list of formulae depended on by this formula that aren't