Support singleton alias

refs: #187

Author: tk0miya

lib/rbs/inline/writer.rb

@@ -497,10 +497,11 @@ def translate_member(member, decl, rbs)
             comment = RBS::AST::Comment.new(string: member.comments.content(trim: true), location: nil)
           end
 
+          kind = decl ? :singleton : :instance #: RBS::AST::Members::Alias::kind
           rbs << RBS::AST::Members::Alias.new(
             new_name: member.new_name,
             old_name: member.old_name,
-            kind: :instance,
+            kind: kind,
             annotations: [],
             location: nil,
             comment: comment

test/rbs/inline/writer_test.rb

@@ -257,6 +257,11 @@ class Foo
 
         # foo is an alias of bar
         alias :foo :bar
+
+        class << self
+          # self.baz is an alias of self.qux
+          alias baz qux
+        end
       end
     RUBY
 
@@ -266,6 +271,9 @@ class Foo
 
         # foo is an alias of bar
         alias foo bar
+
+        # self.baz is an alias of self.qux
+        alias self.baz self.qux
       end
     RBS
   end