Fix warning message

[Abacn]

The following kind of DoFn no longer issue warning:

class DoFn:
  do_some_work # may intended for side effect for incoming elements and not intended to emit anything

class DoFn:
  if not a
    return # A valid filter pattern
  do_some_thing
  return some_output

#28061 was meant to warn this scenario:

class DoFn:
  do_some_work
  return None # user may assume it will emit a "None" downstream, which is not the case

in addition, the formatting of current warning message is wrong. log.warning(("%s", 's',)) will output ("%s", 's',), not formatted string

Please add a meaningful description for your change here

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[gemini-code-assist]

Summary of Changes

Hello @Abacn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves an issue where a warning message was not being displayed correctly due to improper argument handling in the logging function. The change ensures that the warning message's components are unpacked as individual arguments, allowing the logger to format and present the message as intended.

Highlights

• Warning Message Fix: Corrected the argument passing for _LOGGER.warning calls in _check_fn_use_yield_and_return by unpacking the return_none_warning variable, ensuring proper formatting of the warning message.

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[Abacn]

R: @hjtran @damccorm @liferoad

[github-actions]

Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control. If you'd like to restart, comment assign set of reviewers

[damccorm]

Maybe we can even skip this case? It seems like the only potentially problematic case is when they're expecting None to be processed downstream, in this case I think they probably have correct expectations

[Abacn]

yeah, updated. now both "return" and "return sth" will go to "has_return" (we still need to track all return statements to issue warning in the case both yield and return are used)

[damccorm]

Suggested change

	if lstripped_line.startswith("return None"):
	if lstripped_line == "return None":

I actually think we want to do this, because return None, 'foo' is actually a valid way to return a Tuple

[damccorm]

Can this condition now just be:

if has_return_none

We already know that if has_return_none is true, then has_yield is false (otherwise we would've early returned). I think even if there is a mix of return and return None, we probably still want the warning.

[damccorm]

Do we need to print this tuple?

[damccorm]

I think we can get rid of this else and always set has_return to True here (related to comment about condition below)