✨ Convert symbols & ranges in search return opts

lib/net/imap.rb

@@ -1992,7 +1992,9 @@ def uid_expunge(uid_set)
     # ==== Argument translation
     #
     # [+return+ options]
-    #   Must be an Array.  Return option names are strings.
+    #   Must be an Array.  Return option names may be either strings or symbols.
+    #   +Range+ elements which begin and end with negative integers are encoded
+    #   for use with +PARTIAL+--any other ranges are converted to SequenceSet.
     #   Unlike +criteria+, other return option arguments are not automatically
     #   converted to SequenceSet.
     #
@@ -3265,10 +3267,28 @@ def search_args(keys, charset_arg = nil, return: nil, charset: nil)
     end
 
     def convert_return_opts(unconverted)
-      Array.try_convert(unconverted) or
+      return_opts = Array.try_convert(unconverted) or
         raise TypeError, "expected return options to be Array, got %s" % [
           unconverted.class
         ]
+      return_opts.map {|opt|
+        case opt
+        when Symbol then opt.to_s
+        when Range  then partial_range_last_or_seqset(opt)
+        else             opt
+        end
+      }
+    end
+
+    def partial_range_last_or_seqset(range)
+      case [range.begin, range.end]
+      in [Integer => first, Integer => last] if first.negative? && last.negative?
+        # partial-range-last [RFC9394]
+        first <= last or raise DataFormatError, "empty range: %p" % [range]
+        "#{first}:#{last}"
+      else
+        SequenceSet[range]
+      end
     end
 
     def search_internal(cmd, ...)

test/net/imap/test_imap.rb

@@ -1277,6 +1277,18 @@ def seqset_coercible.to_sequence_set
       )
       cmd = server.commands.pop
       assert_equal "RETURN (PARTIAL -500:-1) UID 1234:*", cmd.args
+
+      assert_equal search_result, imap.search(
+        ["UID", 1234..], return: [:PARTIAL, "-500:-1"]
+      )
+      cmd = server.commands.pop
+      assert_equal "RETURN (PARTIAL -500:-1) UID 1234:*", cmd.args
+
+      assert_equal search_result, imap.search(
+        ["UID", 1234..], return: [:PARTIAL, -500..-1, :FOO, 1..]
+      )
+      cmd = server.commands.pop
+      assert_equal "RETURN (PARTIAL -500:-1 FOO 1:*) UID 1234:*", cmd.args
     end
   end