require 'erb'
require 'set'
require 'enumerator'
require 'stringio'
require 'strscan'
require 'rbconfig'
require 'haml/root'
module Haml
# A module containing various useful functions.
module Util
extend self
# An array of ints representing the Ruby version number.
# @api public
RUBY_VERSION = ::RUBY_VERSION.split(".").map {|s| s.to_i}
# Returns the path of a file relative to the Haml root directory.
#
# @param file [String] The filename relative to the Haml root
# @return [String] The filename relative to the the working directory
def scope(file)
File.join(Haml::ROOT_DIR, file)
end
# Converts an array of `[key, value]` pairs to a hash.
#
# @example
# to_hash([[:foo, "bar"], [:baz, "bang"]])
# #=> {:foo => "bar", :baz => "bang"}
# @param arr [Array<(Object, Object)>] An array of pairs
# @return [Hash] A hash
def to_hash(arr)
Hash[arr.compact]
end
# Maps the keys in a hash according to a block.
#
# @example
# map_keys({:foo => "bar", :baz => "bang"}) {|k| k.to_s}
# #=> {"foo" => "bar", "baz" => "bang"}
# @param hash [Hash] The hash to map
# @yield [key] A block in which the keys are transformed
# @yieldparam key [Object] The key that should be mapped
# @yieldreturn [Object] The new value for the key
# @return [Hash] The mapped hash
# @see #map_vals
# @see #map_hash
def map_keys(hash)
to_hash(hash.map {|k, v| [yield(k), v]})
end
# Maps the values in a hash according to a block.
#
# @example
# map_values({:foo => "bar", :baz => "bang"}) {|v| v.to_sym}
# #=> {:foo => :bar, :baz => :bang}
# @param hash [Hash] The hash to map
# @yield [value] A block in which the values are transformed
# @yieldparam value [Object] The value that should be mapped
# @yieldreturn [Object] The new value for the value
# @return [Hash] The mapped hash
# @see #map_keys
# @see #map_hash
def map_vals(hash)
to_hash(hash.map {|k, v| [k, yield(v)]})
end
# Maps the key-value pairs of a hash according to a block.
#
# @example
# map_hash({:foo => "bar", :baz => "bang"}) {|k, v| [k.to_s, v.to_sym]}
# #=> {"foo" => :bar, "baz" => :bang}
# @param hash [Hash] The hash to map
# @yield [key, value] A block in which the key-value pairs are transformed
# @yieldparam [key] The hash key
# @yieldparam [value] The hash value
# @yieldreturn [(Object, Object)] The new value for the `[key, value]` pair
# @return [Hash] The mapped hash
# @see #map_keys
# @see #map_vals
def map_hash(hash, &block)
to_hash(hash.map(&block))
end
# Computes the powerset of the given array.
# This is the set of all subsets of the array.
#
# @example
# powerset([1, 2, 3]) #=>
# Set[Set[], Set[1], Set[2], Set[3], Set[1, 2], Set[2, 3], Set[1, 3], Set[1, 2, 3]]
# @param arr [Enumerable]
# @return [Set<Set>] The subsets of `arr`
def powerset(arr)
arr.inject([Set.new].to_set) do |powerset, el|
new_powerset = Set.new
powerset.each do |subset|
new_powerset << subset
new_powerset << subset + [el]
end
new_powerset
end
end
# Restricts a number to falling within a given range.
# Returns the number if it falls within the range,
# or the closest value in the range if it doesn't.
#
# @param value [Numeric]
# @param range [Range<Numeric>]
# @return [Numeric]
def restrict(value, range)
[[value, range.first].max, range.last].min
end
# Concatenates all strings that are adjacent in an array,
# while leaving other elements as they are.
#
# @example
# merge_adjacent_strings([1, "foo", "bar", 2, "baz"])
# #=> [1, "foobar", 2, "baz"]
# @param arr [Array]
# @return [Array] The enumerable with strings merged
def merge_adjacent_strings(arr)
# Optimize for the common case of one element
return arr if arr.size < 2
arr.inject([]) do |a, e|
if e.is_a?(String)
if a.last.is_a?(String)
a.last << e
else
a << e.dup
end
else
a << e
end
a
end
end
# Intersperses a value in an enumerable, as would be done with `Array#join`
# but without concatenating the array together afterwards.
#
# @param enum [Enumerable]
# @param val
# @return [Array]
def intersperse(enum, val)
enum.inject([]) {|a, e| a << e << val}[0...-1]
end
# Substitutes a sub-array of one array with another sub-array.
#
# @param ary [Array] The array in which to make the substitution
# @param from [Array] The sequence of elements to replace with `to`
# @param to [Array] The sequence of elements to replace `from` with
def substitute(ary, from, to)
res = ary.dup
i = 0
while i < res.size
if res[i...i+from.size] == from
res[i...i+from.size] = to
end
i += 1
end
res
end
# Destructively strips whitespace from the beginning and end
# of the first and last elements, respectively,
# in the array (if those elements are strings).
#
# @param arr [Array]
# @return [Array] `arr`
def strip_string_array(arr)
arr.first.lstrip! if arr.first.is_a?(String)
arr.last.rstrip! if arr.last.is_a?(String)
arr
end
# Return an array of all possible paths through the given arrays.
#
# @param arrs [Array<Array>]
# @return [Array<Arrays>]
#
# @example
# paths([[1, 2], [3, 4], [5]]) #=>
# # [[1, 3, 5],
# # [2, 3, 5],
# # [1, 4, 5],
# # [2, 4, 5]]
def paths(arrs)
arrs.inject([[]]) do |paths, arr|
flatten(arr.map {|e| paths.map {|path| path + [e]}}, 1)
end
end
# Computes a single longest common subsequence for `x` and `y`.
# If there are more than one longest common subsequences,
# the one returned is that which starts first in `x`.
#
# @param x [Array]
# @param y [Array]
# @yield [a, b] An optional block to use in place of a check for equality
# between elements of `x` and `y`.
# @yieldreturn [Object, nil] If the two values register as equal,
# this will return the value to use in the LCS array.
# @return [Array] The LCS
def lcs(x, y, &block)
x = [nil, *x]
y = [nil, *y]
block ||= proc {|a, b| a == b && a}
lcs_backtrace(lcs_table(x, y, &block), x, y, x.size-1, y.size-1, &block)
end
# Returns information about the caller of the previous method.
#
# @param entry [String] An entry in the `#caller` list, or a similarly formatted string
# @return [[String, Fixnum, (String, nil)]] An array containing the filename, line, and method name of the caller.
# The method name may be nil
def caller_info(entry = caller[1])
info = entry.scan(/^(.*?):(-?.*?)(?::.*`(.+)')?$/).first
info[1] = info[1].to_i
# This is added by Rubinius to designate a block, but we don't care about it.
info[2].sub!(/ \{\}\Z/, '') if info[2]
info
end
# Returns whether one version string represents a more recent version than another.
#
# @param v1 [String] A version string.
# @param v2 [String] Another version string.
# @return [Boolean]
def version_gt(v1, v2)
# Construct an array to make sure the shorter version is padded with nil
Array.new([v1.length, v2.length].max).zip(v1.split("."), v2.split(".")) do |_, p1, p2|
p1 ||= "0"
p2 ||= "0"
release1 = p1 =~ /^[0-9]+$/
release2 = p2 =~ /^[0-9]+$/
if release1 && release2
# Integer comparison if both are full releases
p1, p2 = p1.to_i, p2.to_i
next if p1 == p2
return p1 > p2
elsif !release1 && !release2
# String comparison if both are prereleases
next if p1 == p2
return p1 > p2
else
# If only one is a release, that one is newer
return release1
end
end
end
# Returns whether one version string represents the same or a more
# recent version than another.
#
# @param v1 [String] A version string.
# @param v2 [String] Another version string.
# @return [Boolean]
def version_geq(v1, v2)
version_gt(v1, v2) || !version_gt(v2, v1)
end
# A wrapper for `Marshal.dump` that calls `#_before_dump` on the object
# before dumping it, `#_after_dump` afterwards.
# It also calls `#_around_dump` and passes it a block in which the object is dumped.
#
# If any of these methods are undefined, they are not called.
#
# @param obj [Object] The object to dump.
# @return [String] The dumped data.
def dump(obj)
obj._before_dump if obj.respond_to?(:_before_dump)
return Marshal.dump(obj) unless obj.respond_to?(:_around_dump)
res = nil
obj._around_dump {res = Marshal.dump(obj)}
res
ensure
obj._after_dump if obj.respond_to?(:_after_dump)
end
# A wrapper for `Marshal.load` that calls `#_after_load` on the object
# after loading it, if it's defined.
#
# @param data [String] The data to load.
# @return [Object] The loaded object.
def load(data)
obj = Marshal.load(data)
obj._after_load if obj.respond_to?(:_after_load)
obj
end
# Throws a NotImplementedError for an abstract method.
#
# @param obj [Object] `self`
# @raise [NotImplementedError]
def abstract(obj)
raise NotImplementedError.new("#{obj.class} must implement ##{caller_info[2]}")
end
# Silence all output to STDERR within a block.
#
# @yield A block in which no output will be printed to STDERR
def silence_warnings
the_real_stderr, $stderr = $stderr, StringIO.new
yield
ensure
$stderr = the_real_stderr
end
@@silence_warnings = false
# Silences all Haml warnings within a block.
#
# @yield A block in which no Haml warnings will be printed
def silence_haml_warnings
old_silence_warnings = @@silence_warnings
@@silence_warnings = true
yield
ensure
@@silence_warnings = old_silence_warnings
end
# The same as `Kernel#warn`, but is silenced by \{#silence\_haml\_warnings}.
#
# @param msg [String]
def haml_warn(msg)
return if @@silence_warnings
warn(msg)
end
# Try loading Sass. If the `sass` gem isn't installed,
# print a warning and load from the vendored gem.
#
# @return [Boolean] True if Sass was successfully loaded from the `sass` gem,
# false otherwise.
def try_sass
return true if defined?(::SASS_BEGUN_TO_LOAD)
begin
require 'sass/version'
loaded = Sass.respond_to?(:version) && Sass.version[:major] &&
Sass.version[:minor] && ((Sass.version[:major] > 3 && Sass.version[:minor] > 1) ||
((Sass.version[:major] == 3 && Sass.version[:minor] == 1) &&
(Sass.version[:prerelease] || Sass.version[:name] != "Bleeding Edge")))
rescue LoadError => e
loaded = false
end
unless loaded
haml_warn(<<WARNING)
Sass is in the process of being separated from Haml,
and will no longer be bundled at all in Haml 3.2.0.
Please install the 'sass' gem if you want to use Sass.
WARNING
$".delete('sass/version')
$LOAD_PATH.unshift(scope("vendor/sass/lib"))
end
loaded
end
## Cross Rails Version Compatibility
# Returns the root of the Rails application,
# if this is running in a Rails context.
# Returns `nil` if no such root is defined.
#
# @return [String, nil]
def rails_root
if defined?(::Rails.root)
return ::Rails.root.to_s if ::Rails.root
raise "ERROR: Rails.root is nil!"
end
return RAILS_ROOT.to_s if defined?(RAILS_ROOT)
return nil
end
# Returns the environment of the Rails application,
# if this is running in a Rails context.
# Returns `nil` if no such environment is defined.
#
# @return [String, nil]
def rails_env
return ::Rails.env.to_s if defined?(::Rails.env)
return RAILS_ENV.to_s if defined?(RAILS_ENV)
return nil
end
# Returns whether this environment is using ActionPack
# version 3.0.0 or greater.
#
# @return [Boolean]
def ap_geq_3?
ap_geq?("3.0.0.beta1")
end
# Returns whether this environment is using ActionPack
# of a version greater than or equal to that specified.
#
# @param version [String] The string version number to check against.
# Should be greater than or equal to Rails 3,
# because otherwise ActionPack::VERSION isn't autoloaded
# @return [Boolean]
def ap_geq?(version)
# The ActionPack module is always loaded automatically in Rails >= 3
return false unless defined?(ActionPack) && defined?(ActionPack::VERSION) &&
defined?(ActionPack::VERSION::STRING)
version_geq(ActionPack::VERSION::STRING, version)
end
# Returns an ActionView::Template* class.
# In pre-3.0 versions of Rails, most of these classes
# were of the form `ActionView::TemplateFoo`,
# while afterwards they were of the form `ActionView;:Template::Foo`.
#
# @param name [#to_s] The name of the class to get.
# For example, `:Error` will return `ActionView::TemplateError`
# or `ActionView::Template::Error`.
def av_template_class(name)
return ActionView.const_get("Template#{name}") if ActionView.const_defined?("Template#{name}")
return ActionView::Template.const_get(name.to_s)
end
## Rails XSS Safety
# Whether or not ActionView's XSS protection is available and enabled,
# as is the default for Rails 3.0+, and optional for version 2.3.5+.
# Overridden in haml/template.rb if this is the case.
#
# @return [Boolean]
def rails_xss_safe?
false
end
# Returns the given text, marked as being HTML-safe.
# With older versions of the Rails XSS-safety mechanism,
# this destructively modifies the HTML-safety of `text`.
#
# @param text [String, nil]
# @return [String, nil] `text`, marked as HTML-safe
def html_safe(text)
return unless text
return text.html_safe if defined?(ActiveSupport::SafeBuffer)
text.html_safe!
end
# Assert that a given object (usually a String) is HTML safe
# according to Rails' XSS handling, if it's loaded.
#
# @param text [Object]
def assert_html_safe!(text)
return unless rails_xss_safe? && text && !text.to_s.html_safe?
raise Haml::Error.new("Expected #{text.inspect} to be HTML-safe.")
end
# The class for the Rails SafeBuffer XSS protection class.
# This varies depending on Rails version.
#
# @return [Class]
def rails_safe_buffer_class
# It's important that we check ActiveSupport first,
# because in Rails 2.3.6 ActionView::SafeBuffer exists
# but is a deprecated proxy object.
return ActiveSupport::SafeBuffer if defined?(ActiveSupport::SafeBuffer)
return ActionView::SafeBuffer
end
## Cross-OS Compatibility
# Whether or not this is running on Windows.
#
# @return [Boolean]
def windows?
RbConfig::CONFIG['host_os'] =~ /mswin|windows|mingw/i
end
## Cross-Ruby-Version Compatibility
# Whether or not this is running under Ruby 1.8 or lower.
#
# @return [Boolean]
def ruby1_8?
Haml::Util::RUBY_VERSION[0] == 1 && Haml::Util::RUBY_VERSION[1] < 9
end
# Whether or not this is running under Ruby 1.8.6 or lower.
# Note that lower versions are not officially supported.
#
# @return [Boolean]
def ruby1_8_6?
ruby1_8? && Haml::Util::RUBY_VERSION[2] < 7
end
# Checks that the encoding of a string is valid in Ruby 1.9
# and cleans up potential encoding gotchas like the UTF-8 BOM.
# If it's not, yields an error string describing the invalid character
# and the line on which it occurrs.
#
# @param str [String] The string of which to check the encoding
# @yield [msg] A block in which an encoding error can be raised.
# Only yields if there is an encoding error
# @yieldparam msg [String] The error message to be raised
# @return [String] `str`, potentially with encoding gotchas like BOMs removed
def check_encoding(str)
if ruby1_8?
return str.gsub(/\A\xEF\xBB\xBF/, '') # Get rid of the UTF-8 BOM
elsif str.valid_encoding?
# Get rid of the Unicode BOM if possible
if str.encoding.name =~ /^UTF-(8|16|32)(BE|LE)?$/
return str.gsub(Regexp.new("\\A\uFEFF".encode(str.encoding.name)), '')
else
return str
end
end
encoding = str.encoding
newlines = Regexp.new("\r\n|\r|\n".encode(encoding).force_encoding("binary"))
str.force_encoding("binary").split(newlines).each_with_index do |line, i|
begin
line.encode(encoding)
rescue Encoding::UndefinedConversionError => e
yield <<MSG.rstrip, i + 1
Invalid #{encoding.name} character #{e.error_char.dump}
MSG
end
end
return str
end
# Like {\#check\_encoding}, but also checks for a Ruby-style `-# coding:` comment
# at the beginning of the template and uses that encoding if it exists.
#
# The Haml encoding rules are simple.
# If a `-# coding:` comment exists,
# we assume that that's the original encoding of the document.
# Otherwise, we use whatever encoding Ruby has.
#
# Haml uses the same rules for parsing coding comments as Ruby.
# This means that it can understand Emacs-style comments
# (e.g. `-*- encoding: "utf-8" -*-`),
# and also that it cannot understand non-ASCII-compatible encodings
# such as `UTF-16` and `UTF-32`.
#
# @param str [String] The Haml template of which to check the encoding
# @yield [msg] A block in which an encoding error can be raised.
# Only yields if there is an encoding error
# @yieldparam msg [String] The error message to be raised
# @return [String] The original string encoded properly
# @raise [ArgumentError] if the document declares an unknown encoding
def check_haml_encoding(str, &block)
return check_encoding(str, &block) if ruby1_8?
str = str.dup if str.frozen?
bom, encoding = parse_haml_magic_comment(str)
if encoding; str.force_encoding(encoding)
elsif bom; str.force_encoding("UTF-8")
end
return check_encoding(str, &block)
end
unless ruby1_8?
# @private
def _enc(string, encoding)
string.encode(encoding).force_encoding("BINARY")
end
# We could automatically add in any non-ASCII-compatible encodings here,
# but there's not really a good way to do that
# without manually checking that each encoding
# encodes all ASCII characters properly,
# which takes long enough to affect the startup time of the CLI.
ENCODINGS_TO_CHECK = %w[UTF-8 UTF-16BE UTF-16LE UTF-32BE UTF-32LE]
CHARSET_REGEXPS = Hash.new do |h, e|
h[e] =
begin
# /\A(?:\uFEFF)?@charset "(.*?)"|\A(\uFEFF)/
Regexp.new(/\A(?:#{_enc("\uFEFF", e)})?#{
_enc('@charset "', e)}(.*?)#{_enc('"', e)}|\A(#{
_enc("\uFEFF", e)})/)
rescue
# /\A@charset "(.*?)"/
Regexp.new(/\A#{_enc('@charset "', e)}(.*?)#{_enc('"', e)}/)
end
end
end
# Checks to see if a class has a given method.
# For example:
#
# Haml::Util.has?(:public_instance_method, String, :gsub) #=> true
#
# Method collections like `Class#instance_methods`
# return strings in Ruby 1.8 and symbols in Ruby 1.9 and on,
# so this handles checking for them in a compatible way.
#
# @param attr [#to_s] The (singular) name of the method-collection method
# (e.g. `:instance_methods`, `:private_methods`)
# @param klass [Module] The class to check the methods of which to check
# @param method [String, Symbol] The name of the method do check for
# @return [Boolean] Whether or not the given collection has the given method
def has?(attr, klass, method)
klass.send("#{attr}s").include?(ruby1_8? ? method.to_s : method.to_sym)
end
# A version of `Enumerable#enum_with_index` that works in Ruby 1.8 and 1.9.
#
# @param enum [Enumerable] The enumerable to get the enumerator for
# @return [Enumerator] The with-index enumerator
def enum_with_index(enum)
ruby1_8? ? enum.enum_with_index : enum.each_with_index
end
# A version of `Enumerable#enum_cons` that works in Ruby 1.8 and 1.9.
#
# @param enum [Enumerable] The enumerable to get the enumerator for
# @param n [Fixnum] The size of each cons
# @return [Enumerator] The consed enumerator
def enum_cons(enum, n)
ruby1_8? ? enum.enum_cons(n) : enum.each_cons(n)
end
# A version of `Enumerable#enum_slice` that works in Ruby 1.8 and 1.9.
#
# @param enum [Enumerable] The enumerable to get the enumerator for
# @param n [Fixnum] The size of each slice
# @return [Enumerator] The consed enumerator
def enum_slice(enum, n)
ruby1_8? ? enum.enum_slice(n) : enum.each_slice(n)
end
# Returns the ASCII code of the given character.
#
# @param c [String] All characters but the first are ignored.
# @return [Fixnum] The ASCII code of `c`.
def ord(c)
ruby1_8? ? c[0] : c.ord
end
# Flattens the first `n` nested arrays in a cross-version manner.
#
# @param arr [Array] The array to flatten
# @param n [Fixnum] The number of levels to flatten
# @return [Array] The flattened array
def flatten(arr, n)
return arr.flatten(n) unless ruby1_8_6?
return arr if n == 0
arr.inject([]) {|res, e| e.is_a?(Array) ? res.concat(flatten(e, n - 1)) : res << e}
end
# Returns the hash code for a set in a cross-version manner.
# Aggravatingly, this is order-dependent in Ruby 1.8.6.
#
# @param set [Set]
# @return [Fixnum] The order-independent hashcode of `set`
def set_hash(set)
return set.hash unless ruby1_8_6?
set.map {|e| e.hash}.uniq.sort.hash
end
# Tests the hash-equality of two sets in a cross-version manner.
# Aggravatingly, this is order-dependent in Ruby 1.8.6.
#
# @param set1 [Set]
# @param set2 [Set]
# @return [Boolean] Whether or not the sets are hashcode equal
def set_eql?(set1, set2)
return set1.eql?(set2) unless ruby1_8_6?
set1.to_a.uniq.sort_by {|e| e.hash}.eql?(set2.to_a.uniq.sort_by {|e| e.hash})
end
# Like `Object#inspect`, but preserves non-ASCII characters rather than escaping them under Ruby 1.9.2.
# This is necessary so that the precompiled Haml template can be `#encode`d into `@options[:encoding]`
# before being evaluated.
#
# @param obj {Object}
# @return {String}
def inspect_obj(obj)
return obj.inspect unless version_geq(::RUBY_VERSION, "1.9.2")
return ':' + inspect_obj(obj.to_s) if obj.is_a?(Symbol)
return obj.inspect unless obj.is_a?(String)
'"' + obj.gsub(/[\x00-\x7F]+/) {|s| s.inspect[1...-1]} + '"'
end
## Static Method Stuff
# The context in which the ERB for \{#def\_static\_method} will be run.
class StaticConditionalContext
# @param set [#include?] The set of variables that are defined for this context.
def initialize(set)
@set = set
end
# Checks whether or not a variable is defined for this context.
#
# @param name [Symbol] The name of the variable
# @return [Boolean]
def method_missing(name, *args, &block)
super unless args.empty? && block.nil?
@set.include?(name)
end
end
# This is used for methods in {Haml::Buffer} that need to be very fast,
# and take a lot of boolean parameters
# that are known at compile-time.
# Instead of passing the parameters in normally,
# a separate method is defined for every possible combination of those parameters;
# these are then called using \{#static\_method\_name}.
#
# To define a static method, an ERB template for the method is provided.
# All conditionals based on the static parameters
# are done as embedded Ruby within this template.
# For example:
#
# def_static_method(Foo, :my_static_method, [:foo, :bar], :baz, :bang, <<RUBY)
# <% if baz && bang %>
# return foo + bar
# <% elsif baz || bang %>
# return foo - bar
# <% else %>
# return 17
# <% end %>
# RUBY
#
# \{#static\_method\_name} can be used to call static methods.
#
# @overload def_static_method(klass, name, args, *vars, erb)
# @param klass [Module] The class on which to define the static method
# @param name [#to_s] The (base) name of the static method
# @param args [Array<Symbol>] The names of the arguments to the defined methods
# (**not** to the ERB template)
# @param vars [Array<Symbol>] The names of the static boolean variables
# to be made available to the ERB template
# @param erb [String] The template for the method code
def def_static_method(klass, name, args, *vars)
erb = vars.pop
info = caller_info
powerset(vars).each do |set|
context = StaticConditionalContext.new(set).instance_eval {binding}
klass.class_eval(<<METHOD, info[0], info[1])
def #{static_method_name(name, *vars.map {|v| set.include?(v)})}(#{args.join(', ')})
#{ERB.new(erb).result(context)}
end
METHOD
end
end
# Computes the name for a method defined via \{#def\_static\_method}.
#
# @param name [String] The base name of the static method
# @param vars [Array<Boolean>] The static variable assignment
# @return [String] The real name of the static method
def static_method_name(name, *vars)
"#{name}_#{vars.map {|v| !!v}.join('_')}"
end
private
# Calculates the memoization table for the Least Common Subsequence algorithm.
# Algorithm from [Wikipedia](http://en.wikipedia.org/wiki/Longest_common_subsequence_problem#Computing_the_length_of_the_LCS)
def lcs_table(x, y)
c = Array.new(x.size) {[]}
x.size.times {|i| c[i][0] = 0}
y.size.times {|j| c[0][j] = 0}
(1...x.size).each do |i|
(1...y.size).each do |j|
c[i][j] =
if yield x[i], y[j]
c[i-1][j-1] + 1
else
[c[i][j-1], c[i-1][j]].max
end
end
end
return c
end
# Computes a single longest common subsequence for arrays x and y.
# Algorithm from [Wikipedia](http://en.wikipedia.org/wiki/Longest_common_subsequence_problem#Reading_out_an_LCS)
def lcs_backtrace(c, x, y, i, j, &block)
return [] if i == 0 || j == 0
if v = yield(x[i], y[j])
return lcs_backtrace(c, x, y, i-1, j-1, &block) << v
end
return lcs_backtrace(c, x, y, i, j-1, &block) if c[i][j-1] > c[i-1][j]
return lcs_backtrace(c, x, y, i-1, j, &block)
end
# Parses a magic comment at the beginning of a Haml file.
# The parsing rules are basically the same as Ruby's.
#
# @return [(Boolean, String or nil)]
# Whether the document begins with a UTF-8 BOM,
# and the declared encoding of the document (or nil if none is declared)
def parse_haml_magic_comment(str)
scanner = StringScanner.new(str.dup.force_encoding("BINARY"))
bom = scanner.scan(/\xEF\xBB\xBF/n)
return bom unless scanner.scan(/-\s*#\s*/n)
if coding = try_parse_haml_emacs_magic_comment(scanner)
return bom, coding
end
return bom unless scanner.scan(/.*?coding[=:]\s*([\w-]+)/in)
return bom, scanner[1]
end
def try_parse_haml_emacs_magic_comment(scanner)
pos = scanner.pos
return unless scanner.scan(/.*?-\*-\s*/n)
# From Ruby's parse.y
return unless scanner.scan(/([^\s'":;]+)\s*:\s*("(?:\\.|[^"])*"|[^"\s;]+?)[\s;]*-\*-/n)
name, val = scanner[1], scanner[2]
return unless name =~ /(en)?coding/in
val = $1 if val =~ /^"(.*)"$/n
return val
ensure
scanner.pos = pos
end
end
end