Add option regexp_function_cache_class in sqlite adapter

Also add sqlite adapter specs for when setup_regexp_function=cached
option is used.

lib/sequel/adapters/sqlite.rb

@@ -118,6 +118,8 @@ def initialize(opts = OPTS)
       #             it will be called with a string for the regexp and a string
       #             for the value to compare, and should return whether the regexp
       #             matches.
+      # :regexp_function_cache_class :: Defaults to Hash. To avoid a potential
+      #             memory leak, pass ObjectSpace::WeakKeyMap.
       def connect(server)
         opts = server_opts(server)
         opts[:database] = ':memory:' if blank_object?(opts[:database])
@@ -133,7 +135,7 @@ def connect(server)
         connection_pragmas.each{|s| log_connection_yield(s, db){db.execute_batch(s)}}
 
         if typecast_value_boolean(opts[:setup_regexp_function])
-          setup_regexp_function(db, opts[:setup_regexp_function])
+          setup_regexp_function(db, opts[:setup_regexp_function], opts[:regexp_function_cache_class])
         end
 
         class << db
@@ -208,13 +210,22 @@ def adapter_initialize
         set_integer_booleans
       end
 
-      def setup_regexp_function(db, how)
+      def setup_regexp_function(db, how, cache_class)
         case how
         when Proc
           # nothing
         when :cached, "cached"
-          cache = Hash.new{|h,k| h[k] = Regexp.new(k)}
-          how = lambda{|regexp_str, str| cache[regexp_str].match(str)}
+          cache_class ||= Hash
+          cache = cache_class.new
+          how = lambda do |regexp_str, str|
+            if regexp = cache[regexp_str]
+              regexp.match(str)
+            else
+              regexp = Regexp.new(regexp_str)
+              cache[regexp_str] = regexp
+              regexp.match(str)
+            end
+          end
         else
           how = lambda{|regexp_str, str| Regexp.new(regexp_str).match(str)}
         end

spec/adapters/sqlite_spec.rb

@@ -878,3 +878,44 @@
     @db.get(ja.valid).must_equal 1
   end
 end if DB.sqlite_version >= 33800
+
+
+describe 'Regexp support' do
+  before do
+    @db = DB
+
+    @db.create_table(:names) do
+      primary_key :id
+      String :name
+    end
+
+    @db[:names].insert(name: 'Adam')
+    @db[:names].insert(name: 'Jane')
+    @db[:names].insert(name: 'John')
+    @db[:names].insert(name: 'Leo')
+    @db[:names].insert(name: 'Tim')
+    @db[:names].insert(name: 'Tom')
+  end
+  after do
+    @db.drop_table?(:names)
+  end
+
+  it "should support regexp" do
+    @db.must_be :allow_regexp?
+  end
+
+  it "should find by regexp" do
+    names = @db[:names].where(name: /^J/).map { |row| row[:name] }
+    names.must_include 'Jane'
+    names.must_include 'John'
+    names.wont_include 'Adam'
+  end
+
+  it "caches regexp" do
+    before = ObjectSpace.count_objects[:T_REGEXP]
+    @db[:names].where(name: /^J/)
+    after = ObjectSpace.count_objects[:T_REGEXP]
+    diff = after - before
+    diff.must_be :<=, 1
+  end if [:cached, "cached"].include? DB.opts[:setup_regexp_function]
+end if DB.adapter_scheme == :sqlite && DB.opts[:setup_regexp_function]