Deprecate passing arguments to Set#to_set and Enumerable#to_set

Array#to_a, Hash#to_h, Enumerable#to_a, and Enumerable#to_h do not
allow you to specify subclasses.  This has undesired behavior when
passing non-Set subclasses.  All of these are currently allowed, and
none make sense:

```ruby
enum = [1,2,3].to_enum

enum.to_set(Hash)
enum.to_set(Struct.new("A", :a))
enum.to_set(ArgumentError)
enum.to_set(Thread){}
```

Users who want to create instances of a subclass of Set from an
enumerable should pass the enumerable to SetSubclass.new instead of
using to_set.

1 files changed, 15 insertions, 4 deletions

diff --git a/spec/ruby/core/enumerable/to_set_spec.rb b/spec/ruby/core/enumerable/to_set_spec.rb
index 966baae1d9..d0fecf6de4 100644
--- a/spec/ruby/core/enumerable/to_set_spec.rb
+++ b/spec/ruby/core/enumerable/to_set_spec.rb
@@ -11,10 +11,21 @@ describe "Enumerable#to_set" do
     [1, 2, 3].to_set { |x| x * x }.should == Set[1, 4, 9]
   end
 
-  it "instantiates an object of provided as the first argument set class" do
-    set = [1, 2, 3].to_set(EnumerableSpecs::SetSubclass)
-    set.should be_kind_of(EnumerableSpecs::SetSubclass)
-    set.to_a.sort.should == [1, 2, 3]
+  ruby_version_is "3.5" do
+    it "instantiates an object of provided as the first argument set class" do
+      set = nil
+      proc{set = [1, 2, 3].to_set(EnumerableSpecs::SetSubclass)}.should complain(/Enumerable#to_set/)
+      set.should be_kind_of(EnumerableSpecs::SetSubclass)
+      set.to_a.sort.should == [1, 2, 3]
+    end
+  end
+
+  ruby_version_is ""..."3.5" do
+    it "instantiates an object of provided as the first argument set class" do
+      set = [1, 2, 3].to_set(EnumerableSpecs::SetSubclass)
+      set.should be_kind_of(EnumerableSpecs::SetSubclass)
+      set.to_a.sort.should == [1, 2, 3]
+    end
   end
 
   it "does not need explicit `require 'set'`" do