[ruby/irb] Ignore invalid 3 colons in completion

https://github.com/ruby/irb/commit/5e29e3e39c

lib/irb/completion.rb

@@ -286,7 +286,7 @@ module IRB
           all_gvars.grep(Regexp.new(Regexp.quote(gvar)))
         end
 
-      when /^([^."].*)(\.|::)([^.]*)$/
+      when /^([^.:"].*)(\.|::)([^.]*)$/
         # variable.func or func.func
         receiver = $1
         sep = $2

test/irb/test_completion.rb

@@ -32,6 +32,11 @@ module TestIRB
       assert_empty(IRB::InputCompletor.retrieve_completion_data(":irb_unknown_symbol_abcdefg", bind: binding))
     end
 
+    def test_complete_invalid_three_colons
+      assert_empty(IRB::InputCompletor.retrieve_completion_data(":::A", bind: binding))
+      assert_empty(IRB::InputCompletor.retrieve_completion_data(":::", bind: binding))
+    end
+
     def test_complete_symbol_failure
       assert_nil(IRB::InputCompletor::PerfectMatchedProc.(":aiueo", bind: binding))
     end