[EXPERIMENTAL] Declare Ruby files dependencies through magic comments

tasks/mrbgem_spec.rake

@@ -2,6 +2,7 @@ require 'pathname'
 require 'forwardable'
 require 'tsort'
 require 'shellwords'
+require_relative 'utils/rbfiles_sorter'
 
 module MRuby
   module Gem
@@ -58,7 +59,8 @@ module MRuby
         end
         @linker = LinkerConfig.new([], [], [], [], [])
 
-        @rbfiles = Dir.glob("#{@dir}/#{@mrblib_dir}/**/*.rb").sort
+        @rbfiles = RbfilesSorter.new("#{@dir}/#{@mrblib_dir}").sort
+
         @objs = Dir.glob("#{@dir}/#{@objs_dir}/*.{c,cpp,cxx,cc,m,asm,s,S}").map do |f|
           objfile(f.relative_path_from(@dir).to_s.pathmap("#{build_dir}/%X"))
         end

tasks/test/rbfiles_sorter_test.rb

@@ -0,0 +1,28 @@
+require "minitest/autorun"
+
+require_relative "../utils/rbfiles_sorter"
+
+class TestRbfilesSorter < Minitest::Test
+  def test_sort
+    @sorter = RbfilesSorter.new("./support/rbfiles_sorter")
+    sorted = @sorter.sort
+
+    root = File.expand_path("./support/rbfiles_sorter")
+
+    assert_equal "#{root}/stuff/y.rb", sorted[0]
+    assert_equal "#{root}/utils/x.rb", sorted[1]
+    assert_equal "#{root}/b.rb", sorted[2]
+    assert_equal "#{root}/a.rb", sorted[3]
+  end
+
+  def test_sort_without_requires
+    @sorter = RbfilesSorter.new("./support/rbfiles_sorter_2")
+    sorted = @sorter.sort
+
+    root = File.expand_path("./support/rbfiles_sorter_2")
+
+    assert_equal "#{root}/0_x.rb", sorted[0]
+    assert_equal "#{root}/a.rb", sorted[1]
+    assert_equal "#{root}/c.rb", sorted[2]
+  end
+end

tasks/test/support/rbfiles_sorter/a.rb

@@ -0,0 +1,6 @@
+
+# require: "b"
+
+# require: "utils/x.rb"
+
+class A; end

tasks/test/support/rbfiles_sorter/b.rb

@@ -0,0 +1,5 @@
+#require:'utils/x.rb'
+
+module B; end
+
+#require:'utils/y.rb'

tasks/test/support/rbfiles_sorter/stuff/y.rb

@@ -0,0 +1 @@
+module Y; end

tasks/test/support/rbfiles_sorter/utils/x.rb

@@ -0,0 +1,3 @@
+# require: "../stuff/y.rb"
+
+module X; end

tasks/utils/rbfiles_sorter.rb

@@ -0,0 +1,45 @@
+require "tsort"
+
+class RbfilesSorter
+  include TSort
+
+  TAG_RXP = /^#\s*require:\s*['"]([\w\.\/]+)["']\s*$/
+
+  def initialize(root)
+    @root = root
+    @files = Dir.glob("#{root}/**/*.rb").sort
+    @deps = {}
+  end
+
+  def sort
+    @files.each { |f| parse_deps(f) }
+    tsort
+  end
+
+  def tsort_each_child(node, &block)
+    @deps[node].each(&block)
+  end
+
+  def tsort_each_node(&block)
+    @deps.each_key(&block)
+  end
+
+  def parse_deps(file)
+    f = File.new(file)
+
+    deps_list = @deps[File.expand_path(file)] = []
+
+    f.each_line do |line|
+      # Skip blank lines
+      next if line =~ /^\s*$/
+      # All requires should be in the beginning of the file
+      break if line !~ TAG_RXP
+
+      dep = line.match(TAG_RXP)[1]
+
+      dep += ".rb" unless dep.end_with?(".rb")
+
+      deps_list << File.expand_path(dep, File.dirname(file))
+    end
+  end
+end