Allow options to be passed when processing a String pattern

README.md

@@ -72,6 +72,17 @@ called with the results as follows:
 * **Parser**: after completion, the block gets passed the root expression.
   _The result of the block is returned._
 
+All three methods accept either a `Regexp` or `String` (containing the pattern)
+- if a String is passed, `options` can be supplied:
+
+```ruby
+require 'regexp_parser'
+
+Regexp::Parser.parse(
+  "a+ # Recognises a and A...",
+  options: ::Regexp::EXTENDED | ::Regexp::IGNORECASE
+)
+```
 
 ---
 ## Components

lib/regexp_parser/lexer.rb

@@ -11,11 +11,11 @@ class Regexp::Lexer
 
   CLOSING_TOKENS = [:close].freeze
 
-  def self.lex(input, syntax = "ruby/#{RUBY_VERSION}", &block)
-    new.lex(input, syntax, &block)
+  def self.lex(input, syntax = "ruby/#{RUBY_VERSION}", options: nil, &block)
+    new.lex(input, syntax, options: options, &block)
   end
 
-  def lex(input, syntax = "ruby/#{RUBY_VERSION}", &block)
+  def lex(input, syntax = "ruby/#{RUBY_VERSION}", options: nil, &block)
     syntax = Regexp::Syntax.new(syntax)
 
     self.tokens = []
@@ -25,7 +25,7 @@ def lex(input, syntax = "ruby/#{RUBY_VERSION}", &block)
     self.shift = 0
 
     last = nil
-    Regexp::Scanner.scan(input) do |type, token, text, ts, te|
+    Regexp::Scanner.scan(input, options: options) do |type, token, text, ts, te|
       type, token = *syntax.normalize(type, token)
       syntax.check! type, token
 

lib/regexp_parser/parser.rb

@@ -18,12 +18,12 @@ def initialize(type, token)
     end
   end
 
-  def self.parse(input, syntax = "ruby/#{RUBY_VERSION}", &block)
-    new.parse(input, syntax, &block)
+  def self.parse(input, syntax = "ruby/#{RUBY_VERSION}", options: nil, &block)
+    new.parse(input, syntax, options: options, &block)
   end
 
-  def parse(input, syntax = "ruby/#{RUBY_VERSION}", &block)
-    root = Root.build(options_from_input(input))
+  def parse(input, syntax = "ruby/#{RUBY_VERSION}", options: nil, &block)
+    root = Root.build(extract_options(input, options))
 
     self.root = root
     self.node = root
@@ -35,7 +35,7 @@ def parse(input, syntax = "ruby/#{RUBY_VERSION}", &block)
 
     self.captured_group_counts = Hash.new(0)
 
-    Regexp::Lexer.scan(input, syntax) do |token|
+    Regexp::Lexer.scan(input, syntax, options: options) do |token|
       parse_token(token)
     end
 
@@ -54,14 +54,20 @@ def parse(input, syntax = "ruby/#{RUBY_VERSION}", &block)
                 :options_stack, :switching_options, :conditional_nesting,
                 :captured_group_counts
 
-  def options_from_input(input)
-    return {} unless input.is_a?(::Regexp)
+  def extract_options(input, options)
+    if options && !input.is_a?(String)
+      raise ArgumentError, 'options cannot be supplied unless parsing a String'
+    end
+
+    options = input.options if input.is_a?(::Regexp)
+
+    return {} unless options
 
-    options = {}
-    options[:i] = true if input.options & ::Regexp::IGNORECASE != 0
-    options[:m] = true if input.options & ::Regexp::MULTILINE  != 0
-    options[:x] = true if input.options & ::Regexp::EXTENDED   != 0
-    options
+    enabled_options = {}
+    enabled_options[:i] = true if options & ::Regexp::IGNORECASE != 0
+    enabled_options[:m] = true if options & ::Regexp::MULTILINE  != 0
+    enabled_options[:x] = true if options & ::Regexp::EXTENDED   != 0
+    enabled_options
   end
 
   def nest(exp)

lib/regexp_parser/scanner/scanner.rl

@@ -737,21 +737,16 @@ class Regexp::Scanner
   #
   # This method may raise errors if a syntax error is encountered.
   # --------------------------------------------------------------------------
-  def self.scan(input_object, &block)
-    new.scan(input_object, &block)
+  def self.scan(input_object, options: nil, &block)
+    new.scan(input_object, options: options, &block)
   end
 
-  def scan(input_object, &block)
+  def scan(input_object, options: nil, &block)
     self.literal = nil
     stack = []
 
-    if input_object.is_a?(Regexp)
-      input = input_object.source
-      self.free_spacing = (input_object.options & Regexp::EXTENDED != 0)
-    else
-      input = input_object
-      self.free_spacing = false
-    end
+    input = input_object.is_a?(Regexp) ? input_object.source : input_object
+    self.free_spacing = free_spacing?(input_object, options)
     self.spacing_stack = [{:free_spacing => free_spacing, :depth => 0}]
 
     data  = input.unpack("c*") if input.is_a?(String)
@@ -817,6 +812,18 @@ class Regexp::Scanner
   attr_accessor :tokens, :literal, :block, :free_spacing, :spacing_stack,
                 :group_depth, :set_depth, :conditional_stack
 
+  def free_spacing?(input_object, options)
+    if options && !input_object.is_a?(String)
+      raise ArgumentError, 'options cannot be supplied unless scanning a String'
+    end
+
+    options = input_object.options if input_object.is_a?(::Regexp)
+
+    return false unless options
+
+    options & Regexp::EXTENDED != 0
+  end
+
   def in_group?
     group_depth > 0
   end

spec/parser/options_spec.rb

@@ -0,0 +1,28 @@
+require 'spec_helper'
+
+RSpec.describe('passing options to parse') do
+  it 'raises if if parsing from a Regexp and options are passed' do
+    expect { RP.parse(/a+/, options: ::Regexp::EXTENDED) }.to raise_error(
+      ArgumentError,
+      'options cannot be supplied unless parsing a String'
+    )
+  end
+
+  it 'sets options if parsing from a String' do
+    root = RP.parse('a+', options: ::Regexp::MULTILINE | ::Regexp::EXTENDED)
+
+    expect(root.options).to eq(m: true, x: true)
+  end
+
+  it 'allows options to not be supplied when parsing from a Regexp' do
+    root = RP.parse(/a+/ix)
+
+    expect(root.options).to eq(i: true, x: true)
+  end
+
+  it 'has an empty option-hash when parsing from a String and passing no options' do
+    root = RP.parse('a+')
+
+    expect(root.options).to be_empty
+  end
+end

spec/scanner/options_spec.rb

@@ -0,0 +1,36 @@
+require 'spec_helper'
+
+RSpec.describe('passing options to scan') do
+  def expect_type_tokens(tokens, type_tokens)
+    expect(tokens.map { |type, token, *| [type, token] }).to eq(type_tokens)
+  end
+
+  it 'raises if if scanning from a Regexp and options are passed' do
+    expect { RS.scan(/a+/, options: ::Regexp::EXTENDED) }.to raise_error(
+      ArgumentError,
+      'options cannot be supplied unless scanning a String'
+    )
+  end
+
+  it 'sets free_spacing based on options if scanning from a String' do
+    expect_type_tokens(
+      RS.scan('a+#c', options: ::Regexp::MULTILINE | ::Regexp::EXTENDED),
+      [
+        %i[literal literal],
+        %i[quantifier one_or_more],
+        %i[free_space comment]
+      ]
+    )
+  end
+
+  it 'does not set free_spacing if scanning from a String and passing no options' do
+    expect_type_tokens(
+      RS.scan('a+#c'),
+      [
+        %i[literal literal],
+        %i[quantifier one_or_more],
+        %i[literal literal]
+      ]
+    )
+  end
+end