logname may not produce a login name

spec/ruby/library/etc/getlogin_spec.rb:22 から始め、GitHub Actions 環境の JRuby で失敗する Etc.getlogin の例を再現します。利用可能なログイン名取得コマンドと、issue に記載されている環境値を比較し、そのうえで制御端末のない環境を spec が処理できるようにします。コマンドが利用できない場合のフォールバックを維持したまま、JRuby で spec がパスすれば完了です。

Running the specs on JRuby on Github Actions, we see the following message and failing spec:

...
logname: no login name
...
1)
Etc.getlogin returns the name associated with the current login activity FAILED
Expected "runner" == ""
to be truthy but was false
/home/runner/work/jruby/jruby/spec/ruby/library/etc/getlogin_spec.rb:22:in `block in <main>'
...

This can occur when logname is run without a controlling terminal. I'm unsure whether this GHA env is not setting up a tty, or if there's an issue launching the command in JRuby that prevents it inheriting the parent terminal, but it seems like id would be a more reliable command to use:

diff --git a/spec/ruby/library/etc/getlogin_spec.rb b/spec/ruby/library/etc/getlogin_spec.rb
index 7a4fd79ae2..f0dde84ccb 100644
--- a/spec/ruby/library/etc/getlogin_spec.rb
+++ b/spec/ruby/library/etc/getlogin_spec.rb
@@ -18,11 +18,13 @@ describe "Etc.getlogin" do
         else
           # Etc.getlogin returns the same result of logname(2)
           # if it returns non NULL
-          if system("which logname", out: File::NULL, err: File::NULL)
+          if system("which id", out: File::NULL, err: File::NULL)
+            Etc.getlogin.should == `id -un`.chomp
+          elsif system("which logname", out: File::NULL, err: File::NULL)
+            # fallback to `logname` command since `id` is not available
             Etc.getlogin.should == `logname`.chomp
           else
-            # fallback to `id` command since `logname` is not available
-            Etc.getlogin.should == `id -un`.chomp
+            Etc.getlogin.should == ENV['LOGNAME']
           end
         end
       else

However I think we are also stacking too many conditions here. I'm unsure of the "best" way to get the current login, but clearly logname has issues that make it undesirable.

FWIW some forums suggest logname -t which will ensure a tty is created, but this flag is not present on BSD-likes.