[ruby/irb] Display aliases in help message

(https://github.com/ruby/irb/pull/788)

Similar to Pry, it displays user-defined aliases in the help message with
a dedicated section. With the current default aliases, it looks like:

```
...other sections...

Aliases
  $              Alias for `show_source`
  @              Alias for `whereami`
```

https://github.com/ruby/irb/commit/2a0eacc891

1 files changed, 10 insertions, 0 deletions

diff --git a/test/irb/test_cmd.rb b/test/irb/test_cmd.rb
index 62ef7a5b70..55373c2e8a 100644
--- a/test/irb/test_cmd.rb
+++ b/test/irb/test_cmd.rb
@@ -680,6 +680,16 @@ module TestIRB
       assert_match(/List all available commands and their description/, out)
       assert_match(/Start the debugger of debug\.gem/, out)
     end
+
+    def test_show_cmds_list_user_aliases
+      out, err = execute_lines(
+        "show_cmds\n"
+      )
+
+      assert_empty err
+      assert_match(/\$\s+Alias for `show_source`/, out)
+      assert_match(/@\s+Alias for `whereami`/, out)
+    end
   end
 
   class LsTest < CommandTestCase