resolves #3054 never mutate strings; add `frozen_string_literal: true` comment to source files (PR #3055)

- replace gsub! and sub! with gsub and sub, respectively
- add `frozen_string_literal: true` magic comment to all Ruby source files
- see https://www.mikeperham.com/2018/02/28/ruby-optimization-with-one-magic-comment/

72 files changed, 110 insertions, 62 deletions

diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
index 5b908899..278c8fc9 100644
--- a/CHANGELOG.adoc
+++ b/CHANGELOG.adoc
@@ -63,6 +63,7 @@ Improvements::
   * don't store the options attribute on the block once the options are parsed (#3051)
   * add an options method on AbstractNode to retrieve the set of option names (#3051)
   * pass :input_mtime option to Document constructor; let Document constructor assign docdate/time/year attributes (#3029)
+  * never mutate strings; add a `frozen_string_literal: true` magic comment to top of all Ruby source files (#3054)
 
 Bug Fixes::
 
diff --git a/Rakefile b/Rakefile
index 5bff7d4a..799331a2 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 def prepare_test_env
   # rather than hardcoding gc settings in test task,
   # could use https://gist.github.com/benders/788695
diff --git a/bin/asciidoctor b/bin/asciidoctor
index b01aaefb..ef635cfd 100755
--- a/bin/asciidoctor
+++ b/bin/asciidoctor
@@ -1,4 +1,5 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
 
 asciidoctor = File.absolute_path '../lib/asciidoctor.rb', __dir__
 if File.exist? asciidoctor
diff --git a/features/step_definitions.rb b/features/step_definitions.rb
index ebaa9bac..e7aad806 100644
--- a/features/step_definitions.rb
+++ b/features/step_definitions.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 ASCIIDOCTOR_FEATURES_DIR = File.absolute_path __dir__
 ASCIIDOCTOR_LIB_DIR = ENV['ASCIIDOCTOR_LIB_DIR'] || File.join(ASCIIDOCTOR_FEATURES_DIR, '../lib')
 
diff --git a/lib/asciidoctor.rb b/lib/asciidoctor.rb
index bc956b96..64312640 100644
--- a/lib/asciidoctor.rb
+++ b/lib/asciidoctor.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'set'
 
 # NOTE RUBY_ENGINE == 'opal' conditional blocks like this are filtered by the Opal preprocessor
diff --git a/lib/asciidoctor/abstract_block.rb b/lib/asciidoctor/abstract_block.rb
index 18d06274..555c38a6 100644
--- a/lib/asciidoctor/abstract_block.rb
+++ b/lib/asciidoctor/abstract_block.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 class AbstractBlock < AbstractNode
   # Public: Get the Array of Asciidoctor::AbstractBlock sub-blocks for this block
diff --git a/lib/asciidoctor/abstract_node.rb b/lib/asciidoctor/abstract_node.rb
index 39202e01..bb173d88 100644
--- a/lib/asciidoctor/abstract_node.rb
+++ b/lib/asciidoctor/abstract_node.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: An abstract base class that provides state and methods for managing a
 # node of AsciiDoc content. The state and methods on this class are common to
diff --git a/lib/asciidoctor/attribute_list.rb b/lib/asciidoctor/attribute_list.rb
index 92bad194..c9f1f57b 100644
--- a/lib/asciidoctor/attribute_list.rb
+++ b/lib/asciidoctor/attribute_list.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: Handles parsing AsciiDoc attribute lists into a Hash of key/value
 # pairs. By default, attributes must each be separated by a comma and quotes
diff --git a/lib/asciidoctor/block.rb b/lib/asciidoctor/block.rb
index 78fc4bc0..9fad2f65 100644
--- a/lib/asciidoctor/block.rb
+++ b/lib/asciidoctor/block.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: Methods for managing blocks of Asciidoc content in a section.
 #
diff --git a/lib/asciidoctor/callouts.rb b/lib/asciidoctor/callouts.rb
index 0ce7287a..65c2d359 100644
--- a/lib/asciidoctor/callouts.rb
+++ b/lib/asciidoctor/callouts.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: Maintains a catalog of callouts and their associations.
 class Callouts
diff --git a/lib/asciidoctor/cli.rb b/lib/asciidoctor/cli.rb
index f666b4e9..045bb9b8 100644
--- a/lib/asciidoctor/cli.rb
+++ b/lib/asciidoctor/cli.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'optparse'
 require_relative 'cli/options'
 require_relative 'cli/invoker'
diff --git a/lib/asciidoctor/cli/invoker.rb b/lib/asciidoctor/cli/invoker.rb
index ed80d701..7bbc080b 100644
--- a/lib/asciidoctor/cli/invoker.rb
+++ b/lib/asciidoctor/cli/invoker.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
   module Cli
     # Public Invocation class for starting Asciidoctor via CLI
diff --git a/lib/asciidoctor/cli/options.rb b/lib/asciidoctor/cli/options.rb
index d30fe884..1c699dc8 100644
--- a/lib/asciidoctor/cli/options.rb
+++ b/lib/asciidoctor/cli/options.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
   module Cli
     FS = '/'
diff --git a/lib/asciidoctor/converter.rb b/lib/asciidoctor/converter.rb
index 91063c70..91703a29 100644
--- a/lib/asciidoctor/converter.rb
+++ b/lib/asciidoctor/converter.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # A module for defining converters that are used to convert {AbstractNode} objects in a parsed AsciiDoc document to an
 # output (aka backend) format such as HTML or DocBook.
@@ -182,9 +183,8 @@ module Converter
       default.create backend, opts
     end
 
-    # Public: Register a custom converter with this factory to handle conversion to the specified backends. If the
-    # backend value is an asterisk (i.e., +*+), the converter is used as a catch all to handle any backend for which a
-    # converter is not registered.
+    # Public: Register a custom converter with this factory to handle conversion for the specified backends. If the
+    # backend is an asterisk (i.e., +*+), the converter will handle any backend for which a converter is not registered.
     #
     # converter - The Converter class to register.
     # backends  - One or more String backend names that this converter should be registered to handle.
diff --git a/lib/asciidoctor/converter/composite.rb b/lib/asciidoctor/converter/composite.rb
index 9aa927d2..610e91d2 100644
--- a/lib/asciidoctor/converter/composite.rb
+++ b/lib/asciidoctor/converter/composite.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # A {Converter} implementation that delegates to the chain of {Converter}
 # objects passed to the constructor. Selects the first {Converter} that
diff --git a/lib/asciidoctor/converter/docbook5.rb b/lib/asciidoctor/converter/docbook5.rb
index 80743a31..86569f28 100644
--- a/lib/asciidoctor/converter/docbook5.rb
+++ b/lib/asciidoctor/converter/docbook5.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # A built-in {Converter} implementation that generates DocBook 5 output. The output is inspired by the output produced
 # by the docbook45 backend from AsciiDoc Python, except it has been migrated to the DocBook 5 specification.
diff --git a/lib/asciidoctor/converter/html5.rb b/lib/asciidoctor/converter/html5.rb
index 37e6949f..3bdc9f7e 100644
--- a/lib/asciidoctor/converter/html5.rb
+++ b/lib/asciidoctor/converter/html5.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # A built-in {Converter} implementation that generates HTML 5 output
 # consistent with the html5 backend from AsciiDoc Python.
diff --git a/lib/asciidoctor/converter/manpage.rb b/lib/asciidoctor/converter/manpage.rb
index d0ccfe58..f835a617 100644
--- a/lib/asciidoctor/converter/manpage.rb
+++ b/lib/asciidoctor/converter/manpage.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # A built-in {Converter} implementation that generates the man page (troff) format.
 #
diff --git a/lib/asciidoctor/converter/template.rb b/lib/asciidoctor/converter/template.rb
index 78958ceb..8d5bd971 100644
--- a/lib/asciidoctor/converter/template.rb
+++ b/lib/asciidoctor/converter/template.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # A {Converter} implementation that uses templates composed in template
 # languages supported by {https://github.com/rtomayko/tilt Tilt} to convert
diff --git a/lib/asciidoctor/core_ext.rb b/lib/asciidoctor/core_ext.rb
index c5a570dd..76a0fa00 100644
--- a/lib/asciidoctor/core_ext.rb
+++ b/lib/asciidoctor/core_ext.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'core_ext/float/truncate'
 require_relative 'core_ext/match_data/names' if RUBY_ENGINE == 'opal'
 require_relative 'core_ext/nil_or_empty'
diff --git a/lib/asciidoctor/core_ext/float/truncate.rb b/lib/asciidoctor/core_ext/float/truncate.rb
index 96662aa9..5fca64e5 100644
--- a/lib/asciidoctor/core_ext/float/truncate.rb
+++ b/lib/asciidoctor/core_ext/float/truncate.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # NOTE remove once minimum required Ruby version is at least 2.4
 Float.prepend(Module.new do
   def truncate *args
diff --git a/lib/asciidoctor/core_ext/match_data/names.rb b/lib/asciidoctor/core_ext/match_data/names.rb
index 7656a705..ee61e077 100644
--- a/lib/asciidoctor/core_ext/match_data/names.rb
+++ b/lib/asciidoctor/core_ext/match_data/names.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # NOTE remove once implemented in Opal
 class MatchData
   def names
diff --git a/lib/asciidoctor/core_ext/nil_or_empty.rb b/lib/asciidoctor/core_ext/nil_or_empty.rb
index 6c56f958..bed6f5fc 100644
--- a/lib/asciidoctor/core_ext/nil_or_empty.rb
+++ b/lib/asciidoctor/core_ext/nil_or_empty.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # A core library extension that defines the method nil_or_empty? as an alias to
 # optimize checks for nil? or empty? on common object types such as NilClass,
 # String, Array, Hash, and Numeric.
diff --git a/lib/asciidoctor/core_ext/regexp/is_match.rb b/lib/asciidoctor/core_ext/regexp/is_match.rb
index 36bdde73..44edd567 100644
--- a/lib/asciidoctor/core_ext/regexp/is_match.rb
+++ b/lib/asciidoctor/core_ext/regexp/is_match.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # NOTE remove once minimum required Ruby version is at least 2.4
 class Regexp
   alias match? ===
diff --git a/lib/asciidoctor/document.rb b/lib/asciidoctor/document.rb
index 41f305b9..bad2ae1b 100644
--- a/lib/asciidoctor/document.rb
+++ b/lib/asciidoctor/document.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: The Document class represents a parsed AsciiDoc document.
 #
diff --git a/lib/asciidoctor/extensions.rb b/lib/asciidoctor/extensions.rb
index 7cb250e2..72601ee4 100644
--- a/lib/asciidoctor/extensions.rb
+++ b/lib/asciidoctor/extensions.rb
@@ -1,4 +1,4 @@
-# allow `require 'asciidoctor/extensions'` to be used to fully load asciidoctor gem
+# frozen_string_literal: true
 (require 'asciidoctor' unless defined? Asciidoctor.load) unless RUBY_ENGINE == 'opal'
 
 module Asciidoctor
diff --git a/lib/asciidoctor/helpers.rb b/lib/asciidoctor/helpers.rb
index e5dd9265..3fefd5eb 100644
--- a/lib/asciidoctor/helpers.rb
+++ b/lib/asciidoctor/helpers.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Internal: Except where noted, a module that contains internal helper functions.
 module Helpers
diff --git a/lib/asciidoctor/inline.rb b/lib/asciidoctor/inline.rb
index c0f0e6fe..3c7b39b0 100644
--- a/lib/asciidoctor/inline.rb
+++ b/lib/asciidoctor/inline.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: Methods for managing inline elements in AsciiDoc block
 class Inline < AbstractNode
diff --git a/lib/asciidoctor/list.rb b/lib/asciidoctor/list.rb
index fa068be6..af734236 100644
--- a/lib/asciidoctor/list.rb
+++ b/lib/asciidoctor/list.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: Methods for managing AsciiDoc lists (ordered, unordered and description lists)
 class List < AbstractBlock
diff --git a/lib/asciidoctor/logging.rb b/lib/asciidoctor/logging.rb
index 036004b9..82674343 100644
--- a/lib/asciidoctor/logging.rb
+++ b/lib/asciidoctor/logging.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'logger'
 
 module Asciidoctor
diff --git a/lib/asciidoctor/parser.rb b/lib/asciidoctor/parser.rb
index 8aac70d3..183c47ff 100644
--- a/lib/asciidoctor/parser.rb
+++ b/lib/asciidoctor/parser.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Internal: Methods to parse lines of AsciiDoc into an object hierarchy
 # representing the structure of the document. All methods are class methods and
@@ -2680,15 +2681,19 @@ class Parser
           line
         elsif (tab_idx = line.index TAB)
           if tab_idx == 0
-            line = line.sub(TabIndentRx) { full_tab_space * $&.length }
+            leading_tabs = 0
+            line.each_byte do |b|
+              break unless b == 9
+              leading_tabs += 1
+            end
+            line = %(#{full_tab_space * leading_tabs}#{line.slice leading_tabs, line.length})
             next line unless line.include? TAB
           end
           # keeps track of how many spaces were added to adjust offset in match data
           spaces_added = 0
-          idx = -1
+          idx = 0
           result = ''
           line.each_char do |c|
-            idx += 1
             if c == TAB
               # calculate how many spaces this tab represents, then replace tab with spaces
               if (offset = idx + spaces_added) % tab_size == 0
@@ -2703,6 +2708,7 @@ class Parser
             else
               result = result + c
             end
+            idx += 1
           end
           result
         else
diff --git a/lib/asciidoctor/path_resolver.rb b/lib/asciidoctor/path_resolver.rb
index f5d3d5d9..ba86ff88 100644
--- a/lib/asciidoctor/path_resolver.rb
+++ b/lib/asciidoctor/path_resolver.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: Handles all operations for resolving, cleaning and joining paths.
 # This class includes operations for handling both web paths (request URIs) and
diff --git a/lib/asciidoctor/reader.rb b/lib/asciidoctor/reader.rb
index 34967dc5..0da25470 100644
--- a/lib/asciidoctor/reader.rb
+++ b/lib/asciidoctor/reader.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: Methods for retrieving lines from AsciiDoc source files
 class Reader
diff --git a/lib/asciidoctor/rouge_ext.rb b/lib/asciidoctor/rouge_ext.rb
index 9f63af2a..8af4154e 100644
--- a/lib/asciidoctor/rouge_ext.rb
+++ b/lib/asciidoctor/rouge_ext.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'rouge' unless defined? Rouge.version
 
 module Asciidoctor; module RougeExt; module Formatters
diff --git a/lib/asciidoctor/section.rb b/lib/asciidoctor/section.rb
index f116fead..d67131c1 100644
--- a/lib/asciidoctor/section.rb
+++ b/lib/asciidoctor/section.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: Methods for managing sections of AsciiDoc content in a document.
 # The section responds as an Array of content blocks by delegating
diff --git a/lib/asciidoctor/stylesheets.rb b/lib/asciidoctor/stylesheets.rb
index 7d0a7dd4..3b04a2d7 100644
--- a/lib/asciidoctor/stylesheets.rb
+++ b/lib/asciidoctor/stylesheets.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # A utility class for working with the built-in stylesheets.
 #--
diff --git a/lib/asciidoctor/substitutors.rb b/lib/asciidoctor/substitutors.rb
index 6e138574..e4dd264b 100644
--- a/lib/asciidoctor/substitutors.rb
+++ b/lib/asciidoctor/substitutors.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: Methods to perform substitutions on lines of AsciiDoc text. This module
 # is intented to be mixed-in to Section and Block to provide operations for performing
@@ -330,58 +331,32 @@ module Substitutors
     passes.clear if outer
   end
 
-  if RUBY_ENGINE == 'opal'
-    def sub_quotes text
-      if QuotedTextSniffRx[compat = @document.compat_mode].match? text
-        QUOTE_SUBS[compat].each do |type, scope, pattern|
-          text = text.gsub(pattern) { convert_quoted_text $~, type, scope }
-        end
-      end
-      text
-    end
-
-    def sub_replacements text
-      if ReplaceableTextRx.match? text
-        REPLACEMENTS.each do |pattern, replacement, restore|
-          text = text.gsub(pattern) { do_replacement $~, replacement, restore }
-        end
-      end
-      text
-    end
-  else
-    # Public: Substitute quoted text (includes emphasis, strong, monospaced, etc)
-    #
-    # text - The String text to process
-    #
-    # returns The converted String text
-    def sub_quotes text
-      if QuotedTextSniffRx[compat = @document.compat_mode].match? text
-        # NOTE interpolation is faster than String#dup
-        text = %(#{text})
-        QUOTE_SUBS[compat].each do |type, scope, pattern|
-          # NOTE using gsub! here as an MRI Ruby optimization
-          text.gsub!(pattern) { convert_quoted_text $~, type, scope }
-        end
+  # Public: Substitute quoted text (includes emphasis, strong, monospaced, etc.)
+  #
+  # text - The String text to process
+  #
+  # returns The converted [String] text
+  def sub_quotes text
+    if QuotedTextSniffRx[compat = @document.compat_mode].match? text
+      QUOTE_SUBS[compat].each do |type, scope, pattern|
+        text = text.gsub(pattern) { convert_quoted_text $~, type, scope }
       end
-      text
     end
+    text
+  end
 
-    # Public: Substitute replacement characters (e.g., copyright, trademark, etc)
-    #
-    # text - The String text to process
-    #
-    # returns The String text with the replacement characters substituted
-    def sub_replacements text
-      if ReplaceableTextRx.match? text
-        # NOTE interpolation is faster than String#dup
-        text = %(#{text})
-        REPLACEMENTS.each do |pattern, replacement, restore|
-          # NOTE Using gsub! as optimization
-          text.gsub!(pattern) { do_replacement $~, replacement, restore }
-        end
+  # Public: Substitute replacement characters (e.g., copyright, trademark, etc.)
+  #
+  # text - The String text to process
+  #
+  # returns The [String] text with the replacement characters substituted
+  def sub_replacements text
+    if ReplaceableTextRx.match? text
+      REPLACEMENTS.each do |pattern, replacement, restore|
+        text = text.gsub(pattern) { do_replacement $~, replacement, restore }
       end
-      text
     end
+    text
   end
 
   # Public: Substitute special characters (i.e., encode XML)
diff --git a/lib/asciidoctor/syntax_highlighter.rb b/lib/asciidoctor/syntax_highlighter.rb
index 9ab6e3fb..6e29f0e6 100644
--- a/lib/asciidoctor/syntax_highlighter.rb
+++ b/lib/asciidoctor/syntax_highlighter.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: A pluggable adapter for integrating a syntax (aka code) highlighter into AsciiDoc processing.
 #
@@ -49,7 +50,7 @@ module SyntaxHighlighter
   # node   - The source Block to syntax highlight.
   # source - The raw source text String of this source block (after preprocessing).
   # lang   - The source language String specified on this block (e.g., ruby).
-  # opts   - A Hash of options that control syntax highlighting:
+  # opts   - A Hash of options that configure the syntax highlighting:
   #          :callouts - A Hash of callouts extracted from the source, indexed by line number (1-based) (optional).
   #          :css_mode - The Symbol CSS mode (:class or :inline).
   #          :highlight_lines - A 1-based Array of Integer line numbers to highlight (aka emphasize) (optional).
@@ -74,9 +75,8 @@ module SyntaxHighlighter
     raise ::NotImplementedError, %(#{SyntaxHighlighter} subclass #{self.class} must implement the ##{__method__} method)
   end
 
-  # Public: Indicates whether this syntax highlighter wants to write a stylesheet to disk.
-  #
-  # Only called if both the linkcss and copycss attributes are set on the document.
+  # Public: Indicates whether this syntax highlighter wants to write a stylesheet to disk. Only called if both the
+  # linkcss and copycss attributes are set on the document.
   #
   # doc - The Document in which this syntax highlighter is being used.
   #
diff --git a/lib/asciidoctor/syntax_highlighter/coderay.rb b/lib/asciidoctor/syntax_highlighter/coderay.rb
index d5f94bda..9fe7a56a 100644
--- a/lib/asciidoctor/syntax_highlighter/coderay.rb
+++ b/lib/asciidoctor/syntax_highlighter/coderay.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 class SyntaxHighlighter::CodeRayAdapter < SyntaxHighlighter::Base
   register_for 'coderay'
diff --git a/lib/asciidoctor/syntax_highlighter/highlightjs.rb b/lib/asciidoctor/syntax_highlighter/highlightjs.rb
index e89043c4..452913cd 100644
--- a/lib/asciidoctor/syntax_highlighter/highlightjs.rb
+++ b/lib/asciidoctor/syntax_highlighter/highlightjs.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 class SyntaxHighlighter::HighlightJsAdapter < SyntaxHighlighter::Base
   register_for 'highlightjs', 'highlight.js'
diff --git a/lib/asciidoctor/syntax_highlighter/html_pipeline.rb b/lib/asciidoctor/syntax_highlighter/html_pipeline.rb
index f0342d43..d2679262 100644
--- a/lib/asciidoctor/syntax_highlighter/html_pipeline.rb
+++ b/lib/asciidoctor/syntax_highlighter/html_pipeline.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 class SyntaxHighlighter::HtmlPipelineAdapter < SyntaxHighlighter::Base
   register_for 'html-pipeline'
diff --git a/lib/asciidoctor/syntax_highlighter/prettify.rb b/lib/asciidoctor/syntax_highlighter/prettify.rb
index b78ce55a..c3d06e95 100644
--- a/lib/asciidoctor/syntax_highlighter/prettify.rb
+++ b/lib/asciidoctor/syntax_highlighter/prettify.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 class SyntaxHighlighter::PrettifyAdapter < SyntaxHighlighter::Base
   register_for 'prettify'
diff --git a/lib/asciidoctor/syntax_highlighter/pygments.rb b/lib/asciidoctor/syntax_highlighter/pygments.rb
index 2f4a614e..191acb31 100644
--- a/lib/asciidoctor/syntax_highlighter/pygments.rb
+++ b/lib/asciidoctor/syntax_highlighter/pygments.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 class SyntaxHighlighter::PygmentsAdapter < SyntaxHighlighter::Base
   register_for 'pygments'
diff --git a/lib/asciidoctor/syntax_highlighter/rouge.rb b/lib/asciidoctor/syntax_highlighter/rouge.rb
index 95268a5b..cb60824e 100644
--- a/lib/asciidoctor/syntax_highlighter/rouge.rb
+++ b/lib/asciidoctor/syntax_highlighter/rouge.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 class SyntaxHighlighter::RougeAdapter < SyntaxHighlighter::Base
   register_for 'rouge'
diff --git a/lib/asciidoctor/table.rb b/lib/asciidoctor/table.rb
index 62d4521f..8ed762c5 100644
--- a/lib/asciidoctor/table.rb
+++ b/lib/asciidoctor/table.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # Public: Methods and constants for managing AsciiDoc table content in a document.
 # It supports all three of AsciiDoc's table formats: psv, dsv and csv.
diff --git a/lib/asciidoctor/timings.rb b/lib/asciidoctor/timings.rb
index 78b0b1ec..2be2024e 100644
--- a/lib/asciidoctor/timings.rb
+++ b/lib/asciidoctor/timings.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
   class Timings
     def initialize
diff --git a/lib/asciidoctor/version.rb b/lib/asciidoctor/version.rb
index 5ecd8ba7..93a066b4 100644
--- a/lib/asciidoctor/version.rb
+++ b/lib/asciidoctor/version.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
   VERSION = '2.0.0.dev'
 end
diff --git a/lib/asciidoctor/writer.rb b/lib/asciidoctor/writer.rb
index a77037de..abd3e865 100644
--- a/lib/asciidoctor/writer.rb
+++ b/lib/asciidoctor/writer.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module Asciidoctor
 # A module that can be used to mix the {#write} method into a {Converter} implementation to allow the converter to
 # control how the output is written to disk.
diff --git a/test/api_test.rb b/test/api_test.rb
index ee454227..218e63f8 100644
--- a/test/api_test.rb
+++ b/test/api_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'API' do
diff --git a/test/attribute_list_test.rb b/test/attribute_list_test.rb
index d6958b8e..98b3916b 100644
--- a/test/attribute_list_test.rb
+++ b/test/attribute_list_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'AttributeList' do
diff --git a/test/attributes_test.rb b/test/attributes_test.rb
index 2e905b9a..acd2f050 100644
--- a/test/attributes_test.rb
+++ b/test/attributes_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'Attributes' do
@@ -201,7 +202,7 @@ context 'Attributes' do
       {name}
       EOS
       # see https://github.com/oracle/truffleruby/issues/1563
-      input = input.force_encoding ::Encoding::UTF_8 if RUBY_ENGINE == 'truffleruby'
+      input = String.new input, encoding: ::Encoding::UTF_8 if RUBY_ENGINE == 'truffleruby'
 
       result = convert_inline_string input, attributes: { 'max-attribute-value-size' => 6 }
       assert_equal expected, result
@@ -216,7 +217,7 @@ context 'Attributes' do
       {name}
       EOS
       # see https://github.com/oracle/truffleruby/issues/1563
-      input = input.force_encoding ::Encoding::UTF_8 if RUBY_ENGINE == 'truffleruby'
+      input = String.new input, encoding: ::Encoding::UTF_8 if RUBY_ENGINE == 'truffleruby'
 
       result = convert_inline_string input, attributes: { 'max-attribute-value-size' => 8 }
       assert_equal expected, result
diff --git a/test/blocks_test.rb b/test/blocks_test.rb
index 54f6236d..8e76dc38 100644
--- a/test/blocks_test.rb
+++ b/test/blocks_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'Blocks' do
diff --git a/test/converter_test.rb b/test/converter_test.rb
index 35b81be9..b57216fe 100644
--- a/test/converter_test.rb
+++ b/test/converter_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 require 'tilt' unless defined? ::Tilt.new
 
diff --git a/test/document_test.rb b/test/document_test.rb
index 94f4d539..54fffb38 100644
--- a/test/document_test.rb
+++ b/test/document_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 BUILT_IN_ELEMENTS = %w(admonition audio colist dlist document embedded example floating_title image inline_anchor inline_break inline_button inline_callout inline_footnote inline_image inline_indexterm inline_kbd inline_menu inline_quoted listing literal stem olist open page_break paragraph pass preamble quote section sidebar table thematic_break toc ulist verse video)
diff --git a/test/extensions_test.rb b/test/extensions_test.rb
index 0b8dbeeb..2d6cda9e 100644
--- a/test/extensions_test.rb
+++ b/test/extensions_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 class ExtensionsInitTest < Minitest::Test
diff --git a/test/invoker_test.rb b/test/invoker_test.rb
index 1ad7580d..8e09f435 100644
--- a/test/invoker_test.rb
+++ b/test/invoker_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 require_relative 'test_helper'
 require File.join Asciidoctor::LIB_DIR, 'asciidoctor/cli'
 
diff --git a/test/links_test.rb b/test/links_test.rb
index 5e744f48..9a2620df 100644
--- a/test/links_test.rb
+++ b/test/links_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'Links' do
diff --git a/test/lists_test.rb b/test/lists_test.rb
index 4a0c9003..4eeb80be 100644
--- a/test/lists_test.rb
+++ b/test/lists_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context "Bulleted lists (:ulist)" do
diff --git a/test/logger_test.rb b/test/logger_test.rb
index 1b1d81fd..80870d7c 100644
--- a/test/logger_test.rb
+++ b/test/logger_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'Logger' do
diff --git a/test/manpage_test.rb b/test/manpage_test.rb
index d0da15b7..ac8223c3 100644
--- a/test/manpage_test.rb
+++ b/test/manpage_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 SAMPLE_MANPAGE_HEADER = <<'EOS'.chomp
diff --git a/test/options_test.rb b/test/options_test.rb
index 843596fe..54e6980d 100644
--- a/test/options_test.rb
+++ b/test/options_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 require File.join Asciidoctor::LIB_DIR, 'asciidoctor/cli/options'
 
diff --git a/test/paragraphs_test.rb b/test/paragraphs_test.rb
index a58eb16c..f1a864bd 100644
--- a/test/paragraphs_test.rb
+++ b/test/paragraphs_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'Paragraphs' do
diff --git a/test/parser_test.rb b/test/parser_test.rb
index d54d6d30..e5a1d30d 100644
--- a/test/parser_test.rb
+++ b/test/parser_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context "Parser" do
diff --git a/test/paths_test.rb b/test/paths_test.rb
index 292c3fb9..79e4c60a 100644
--- a/test/paths_test.rb
+++ b/test/paths_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'Path Resolver' do
diff --git a/test/preamble_test.rb b/test/preamble_test.rb
index 691dc63a..ef7db9ef 100644
--- a/test/preamble_test.rb
+++ b/test/preamble_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'Preamble' do
diff --git a/test/reader_test.rb b/test/reader_test.rb
index 3b538d2e..45fc7686 100644
--- a/test/reader_test.rb
+++ b/test/reader_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 class ReaderTest < Minitest::Test
@@ -23,7 +24,7 @@ third line
 
       test 'should remove UTF-8 BOM from first line of String data' do
         ['UTF-8', 'ASCII-8BIT'].each do |start_encoding|
-          data = "\xef\xbb\xbf#{SAMPLE_DATA.join ::Asciidoctor::LF}".force_encoding start_encoding
+          data = String.new %(\xef\xbb\xbf#{SAMPLE_DATA.join ::Asciidoctor::LF}), encoding: start_encoding
           reader = Asciidoctor::Reader.new data, nil, normalize: true
           assert_equal Encoding::UTF_8, reader.lines[0].encoding
           assert_equal 'f', reader.lines[0].chr
@@ -34,7 +35,7 @@ third line
       test 'should remove UTF-8 BOM from first line of Array data' do
         ['UTF-8', 'ASCII-8BIT'].each do |start_encoding|
           data = SAMPLE_DATA.dup
-          data[0] = "\xef\xbb\xbf#{data.first}".force_encoding start_encoding
+          data[0] = String.new %(\xef\xbb\xbf#{data.first}), encoding: start_encoding
           reader = Asciidoctor::Reader.new data, nil, normalize: true
           assert_equal Encoding::UTF_8, reader.lines[0].encoding
           assert_equal 'f', reader.lines[0].chr
diff --git a/test/sections_test.rb b/test/sections_test.rb
index ddfabebe..2dca1c07 100644
--- a/test/sections_test.rb
+++ b/test/sections_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'Sections' do
diff --git a/test/substitutions_test.rb b/test/substitutions_test.rb
index c1e0a86c..2c7ccd8d 100644
--- a/test/substitutions_test.rb
+++ b/test/substitutions_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 # TODO
diff --git a/test/syntax_highlighter_test.rb b/test/syntax_highlighter_test.rb
index d2f920cd..9f01f7e1 100644
--- a/test/syntax_highlighter_test.rb
+++ b/test/syntax_highlighter_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'Syntax Highlighter' do
diff --git a/test/tables_test.rb b/test/tables_test.rb
index 6bc39ddd..3f76b8d5 100644
--- a/test/tables_test.rb
+++ b/test/tables_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context 'Tables' do
diff --git a/test/test_helper.rb b/test/test_helper.rb
index fc978f82..a4c53ee0 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 ASCIIDOCTOR_TEST_DIR = File.absolute_path __dir__
 ASCIIDOCTOR_LIB_DIR = ENV['ASCIIDOCTOR_LIB_DIR'] || (File.join ASCIIDOCTOR_TEST_DIR, '../lib')
 
diff --git a/test/text_test.rb b/test/text_test.rb
index daa4a172..882d6a51 100644
--- a/test/text_test.rb
+++ b/test/text_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require_relative 'test_helper'
 
 context "Text" do