Enable frozen string literals

In preparation for frozen string literals being enabled by default in
Ruby (see
ruby/ruby@12be40a),
opt into frozen string literals now and fix any issues raised by running
a full compile and run of the test suite with Ruby's
`--enable-frozen-string-literal --debug-frozen-string-literal` options.

We also take this opportunity to remove the now-redundant encoding
comments as we no longer support Ruby versions that default to anything
except UTF-8.

Gemfile

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source "https://rubygems.org"
 
 gemspec

ext/re2/extconf.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # re2 (https://github.com/mudge/re2)
 # Ruby bindings to RE2, a "fast, safe, thread-friendly alternative to
 # backtracking regular expression engines like those used in PCRE, Perl, and
@@ -126,7 +128,7 @@ def build_extension(static_p = false)
 
   # Pass -x c++ to force gcc to compile the test program
   # as C++ (as it will end in .c by default).
-  compile_options = "-x c++"
+  compile_options = +"-x c++"
 
   have_library("stdc++")
   have_header("stdint.h")

ext/re2/recipes.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # re2 (https://github.com/mudge/re2)
 # Ruby bindings to RE2, a "fast, safe, thread-friendly alternative to
 # backtracking regular expression engines like those used in PCRE, Perl, and

lib/re2.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # re2 (https://github.com/mudge/re2)
 # Ruby bindings to RE2, a "fast, safe, thread-friendly alternative to
 # backtracking regular expression engines like those used in PCRE, Perl, and

lib/re2/regexp.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # re2 (https://github.com/mudge/re2)
 # Ruby bindings to RE2, a "fast, safe, thread-friendly alternative to
 # backtracking regular expression engines like those used in PCRE, Perl, and

lib/re2/scanner.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # re2 (https://github.com/mudge/re2)
 # Ruby bindings to RE2, a "fast, safe, thread-friendly alternative to
 # backtracking regular expression engines like those used in PCRE, Perl, and

lib/re2/string.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # re2 (https://github.com/mudge/re2)
 # Ruby bindings to RE2, a "fast, safe, thread-friendly alternative to
 # backtracking regular expression engines like those used in PCRE, Perl, and

re2.gemspec

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative 'lib/re2/version'
 
 Gem::Specification.new do |s|

scripts/update-dependencies

@@ -1,4 +1,5 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
 
 require "net/http"
 require "digest/sha2"

spec/kernel_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 RSpec.describe Kernel do
   describe ".RE2" do
     it "returns an RE2::Regexp instance given a pattern" do

spec/re2/match_data_spec.rb

@@ -1,4 +1,5 @@
-# encoding: utf-8
+# frozen_string_literal: true
+
 require 'objspace'
 
 RSpec.describe RE2::MatchData do
@@ -142,7 +143,7 @@
     end
 
     it "returns a copy, not the actual original" do
-      string = "bob"
+      string = +"bob"
       re = RE2::Regexp.new('(\D+)').match(string)
 
       expect(re.string).to_not equal(string)
@@ -155,7 +156,7 @@
     end
 
     it "does not copy the string if it was already frozen" do
-      string = "bob".freeze
+      string = "bob"
       re = RE2::Regexp.new('(\D+)').match(string)
 
       expect(re.string).to equal(string)

spec/re2/regexp_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 RSpec.describe RE2::Regexp do
   describe "#initialize" do
     it "returns an instance given only a pattern" do

spec/re2/scanner_spec.rb

@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 RSpec.describe RE2::Scanner do
   describe "#regexp" do

spec/re2/set_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 RSpec.describe RE2::Set do
   describe "#initialize" do
     it "returns an instance given no args" do

spec/re2/string_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "re2/string"
 
 class String

spec/re2_spec.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 RSpec.describe RE2 do
   describe ".Replace" do
     it "only replaces the first occurrence of the pattern" do

spec/spec_helper.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "re2"
 
 # To test passing objects that can be coerced to a String.