From bb216b8758f4d4db0674b2ca0f31e58fbdd6201f Mon Sep 17 00:00:00 2001
From: Marc-Andre Lafortune <github@marc-andre.ca>
Date: Mon, 21 Dec 2020 00:02:26 -0500
Subject: [PATCH] Raise informative error on SortedSet access

---
 lib/set.rb                                    |  2 +
 lib/set/sorted_set.rb                         |  6 +++
 .../fake_sorted_set_gem/sorted_set.rb         |  3 ++
 test/test_sorted_set.rb                       | 45 +++++++++++++++++++
 4 files changed, 56 insertions(+)
 create mode 100644 lib/set/sorted_set.rb
 create mode 100644 test/fixtures/fake_sorted_set_gem/sorted_set.rb
 create mode 100644 test/test_sorted_set.rb

diff --git a/lib/set.rb b/lib/set.rb
index 2c9257d..2bd2a0f 100644
--- a/lib/set.rb
+++ b/lib/set.rb
@@ -690,3 +690,5 @@ def to_set(klass = Set, *args, &block)
     klass.new(self, *args, &block)
   end
 end
+
+autoload :SortedSet, "#{__dir__}/set/sorted_set"
diff --git a/lib/set/sorted_set.rb b/lib/set/sorted_set.rb
new file mode 100644
index 0000000..e4e01ba
--- /dev/null
+++ b/lib/set/sorted_set.rb
@@ -0,0 +1,6 @@
+begin
+  require 'sorted_set'
+rescue ::LoadError
+  raise "The `SortedSet` class has been extracted from the `set` library." \
+        "You must use the `sorted_set` gem or other alternatives."
+end
diff --git a/test/fixtures/fake_sorted_set_gem/sorted_set.rb b/test/fixtures/fake_sorted_set_gem/sorted_set.rb
new file mode 100644
index 0000000..02c9721
--- /dev/null
+++ b/test/fixtures/fake_sorted_set_gem/sorted_set.rb
@@ -0,0 +1,3 @@
+class SortedSet
+  # ...
+end
diff --git a/test/test_sorted_set.rb b/test/test_sorted_set.rb
new file mode 100644
index 0000000..1ac6ee9
--- /dev/null
+++ b/test/test_sorted_set.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: false
+require 'test/unit'
+require 'set'
+
+class TC_SortedSet < Test::Unit::TestCase
+  def base_dir
+    "#{__dir__}/../lib"
+  end
+
+  def assert_runs(ruby, options: nil)
+    options = ['-I', base_dir, *options]
+    r = system(RbConfig.ruby, *options, '-e', ruby)
+    assert(r)
+  end
+
+  def test_error
+    assert_runs <<~RUBY
+      require "set"
+
+      r = begin
+        puts SortedSet.new
+      rescue Exception => e
+        e.message
+      end
+      raise r unless r.match? /has been extracted/
+    RUBY
+  end
+
+  def test_ok_with_gem
+    assert_runs <<~RUBY, options: ['-I', "#{__dir__}/fixtures/fake_sorted_set_gem"]
+      require "set"
+
+      var = SortedSet.new.to_s
+    RUBY
+  end
+
+  def test_ok_require
+    assert_runs <<~RUBY, options: ['-I', "#{__dir__}/fixtures/fake_sorted_set_gem"]
+      require "set"
+      require "sorted_set"
+
+      var = SortedSet.new.to_s
+    RUBY
+  end
+end