define Range#match? if Ruby < 2.4

See the rationale in the documentation included in this patch.

We are going to gradually introduce this predicate in the code base.

activesupport/CHANGELOG.md

+*   Defines `Regexp.match?` for Ruby versions prior to 2.4. The predicate
+    has the same interface, but it does not have the performance boost. It's
+    purpose is to be able to write 2.4 compatible code.
+
+    *Xavier Noria*
+
 *   Allow MessageEncryptor to take advantage of authenticated encryption modes.
 
     AEAD modes like `aes-256-gcm` provide both confidentiality and data

activesupport/lib/active_support/core_ext/regexp.rb

@@ -2,4 +2,8 @@ class Regexp #:nodoc:
   def multiline?
     options & MULTILINE == MULTILINE
   end
+
+  def match?(string, pos=0)
+    !! match(string, pos)
+  end unless //.respond_to?(:match?)
 end

activesupport/test/core_ext/regexp_ext_test.rb

@@ -7,4 +7,28 @@ def test_multiline
     assert_equal false, //.multiline?
     assert_equal false, /(?m:)/.multiline?
   end
+
+  # Based on https://github.com/ruby/ruby/blob/trunk/test/ruby/test_regexp.rb.
+  def test_match_p
+    /back(...)/ =~ 'backref'
+    # must match here, but not in a separate method, e.g., assert_send,
+    # to check if $~ is affected or not.
+    assert_equal false, //.match?(nil)
+    assert_equal true, //.match?("")
+    assert_equal true, /.../.match?(:abc)
+    assert_raise(TypeError) { /.../.match?(Object.new) }
+    assert_equal true, /b/.match?('abc')
+    assert_equal true, /b/.match?('abc', 1)
+    assert_equal true, /../.match?('abc', 1)
+    assert_equal true, /../.match?('abc', -2)
+    assert_equal false, /../.match?("abc", -4)
+    assert_equal false, /../.match?("abc", 4)
+    assert_equal true, /\z/.match?("")
+    assert_equal true, /\z/.match?("abc")
+    assert_equal true, /R.../.match?("Ruby")
+    assert_equal false, /R.../.match?("Ruby", 1)
+    assert_equal false, /P.../.match?("Ruby")
+    assert_equal 'backref', $&
+    assert_equal 'ref', $1
+  end
 end

guides/source/active_support_core_extensions.md

@@ -2916,6 +2916,24 @@ end
 
 NOTE: Defined in `active_support/core_ext/regexp.rb`.
 
+### `match?`
+
+Rails implements `Regexp#match?` for Ruby versions prior to 2.4:
+
+```ruby
+/oo/.match?('foo')    # => true
+/oo/.match?('bar')    # => false
+/oo/.match?('foo', 1) # => true
+```
+
+The backport has the same interface and lack of side-effects in the caller like
+not setting `$1` and friends, but it does not have the speed benefits. Its
+purpose is to be able to write 2.4 compatible code. Rails itself uses this
+predicate internally for example.
+
+Active Support defines `Regexp#match?` only if not present, so code running
+under 2.4 or later does run the original one and gets the performance boost.
+
 Extensions to `Range`
 ---------------------