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require "set"
require "pathname"
require "concurrent/atomic/atomic_boolean"
module ActiveSupport
# Allows you to "listen" to changes in a file system.
# The evented file updater does not hit disk when checking for updates
# instead it uses platform specific file system events to trigger a change
# in state.
#
# The file checker takes an array of files to watch or a hash specifying directories
# and file extensions to watch. It also takes a block that is called when
# EventedFileUpdateChecker#execute is run or when EventedFileUpdateChecker#execute_if_updated
# is run and there have been changes to the file system.
#
# Note: Forking will cause the first call to `updated?` to return `true`.
#
# Example:
#
# checker = ActiveSupport::EventedFileUpdateChecker.new(["/tmp/foo"]) { puts "changed" }
# checker.updated?
# # => false
# checker.execute_if_updated
# # => nil
#
# FileUtils.touch("/tmp/foo")
#
# checker.updated?
# # => true
# checker.execute_if_updated
# # => "changed"
#
class EventedFileUpdateChecker #:nodoc: all
def initialize(files, dirs = {}, &block)
unless block
raise ArgumentError, "A block is required to initialize an EventedFileUpdateChecker"
end
@ph = PathHelper.new
@files = files.map { |f| @ph.xpath(f) }.to_set
@dirs = {}
dirs.each do |dir, exts|
@dirs[@ph.xpath(dir)] = Array(exts).map { |ext| @ph.normalize_extension(ext) }
end
@block = block
@updated = Concurrent::AtomicBoolean.new(false)
@lcsp = @ph.longest_common_subpath(@dirs.keys)
@pid = Process.pid
@boot_mutex = Mutex.new
if (@dtw = directories_to_watch).any?
# Loading listen triggers warnings. These are originated by a legit
# usage of attr_* macros for private attributes, but adds a lot of noise
# to our test suite. Thus, we lazy load it and disable warnings locally.
silence_warnings do
begin
require "listen"
rescue LoadError => e
raise LoadError, "Could not load the 'listen' gem. Add `gem 'listen'` to the development group of your Gemfile", e.backtrace
end
end
end
boot!
end
def updated?
@boot_mutex.synchronize do
if @pid != Process.pid
boot!
@pid = Process.pid
@updated.make_true
end
end
@updated.true?
end
def execute
@updated.make_false
@block.call
end
def execute_if_updated
if updated?
yield if block_given?
execute
true
end
end
private
def boot!
Listen.to(*@dtw, &method(:changed)).start
end
def changed(modified, added, removed)
unless updated?
@updated.make_true if (modified + added + removed).any? { |f| watching?(f) }
end
end
def watching?(file)
file = @ph.xpath(file)
if @files.member?(file)
true
elsif file.directory?
false
else
ext = @ph.normalize_extension(file.extname)
file.dirname.ascend do |dir|
if @dirs.fetch(dir, []).include?(ext)
break true
elsif dir == @lcsp || dir.root?
break false
end
end
end
end
def directories_to_watch
dtw = (@files + @dirs.keys).map { |f| @ph.existing_parent(f) }
dtw.compact!
dtw.uniq!
@ph.filter_out_descendants(dtw)
end
class PathHelper
def xpath(path)
Pathname.new(path).expand_path
end
def normalize_extension(ext)
ext.to_s.sub(/\A\./, "")
end
# Given a collection of Pathname objects returns the longest subpath
# common to all of them, or +nil+ if there is none.
def longest_common_subpath(paths)
return if paths.empty?
lcsp = Pathname.new(paths[0])
paths[1..-1].each do |path|
until ascendant_of?(lcsp, path)
if lcsp.root?
# If we get here a root directory is not an ascendant of path.
# This may happen if there are paths in different drives on
# Windows.
return
else
lcsp = lcsp.parent
end
end
end
lcsp
end
# Returns the deepest existing ascendant, which could be the argument itself.
def existing_parent(dir)
dir.ascend do |ascendant|
break ascendant if ascendant.directory?
end
end
# Filters out directories which are descendants of others in the collection (stable).
def filter_out_descendants(dirs)
return dirs if dirs.length < 2
dirs_sorted_by_nparts = dirs.sort_by { |dir| dir.each_filename.to_a.length }
descendants = []
until dirs_sorted_by_nparts.empty?
dir = dirs_sorted_by_nparts.shift
dirs_sorted_by_nparts.reject! do |possible_descendant|
ascendant_of?(dir, possible_descendant) && descendants << possible_descendant
end
end
# Array#- preserves order.
dirs - descendants
end
private
def ascendant_of?(base, other)
base != other && other.ascend do |ascendant|
break true if base == ascendant
end
end
end
end
end
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