Really nice catch!

Update libphutil/ to clear lint. Those symbols were introduced in a more recent version. If you can't update /usr/local/libphutil, you can put development copies of arcanist/ and libphutil/ next to one another somewhere, then run that version of arc to get clean lint.

This will probably perform even faster:

$rows = array();
foreach ($stuff as $thing) {
  // ...

  $rows[] = $this->renderInlines(...);

  // ..
}

return array_mergev($rows);

Can you try that?

(Note that the final call is array_mergev() not array_merge().)

Oh look at this helpful documentation that some kind soul (who must spend all his time frustrated with PHP) wrote! https://secure.phabricator.com/book/phabflavor/article/php_pitfalls/

Thanks, will update this diff.

Wait, how does your suggestion work? This line means that $rows would be a mix of array objects and phutil_tag objects, so (I think that) you can't pass that into array_mergev.

I also don't know anything about the internals of PHP, but I wouldn't be surprised if no-op'ing on empty arrays is faster than building a giant array where half the entries are empty arrays, and then calling array_mergev. (In general, I'd expect very few lines to have inlines in Diffusion -- those should just be stuff like lint warnings, which should hopefully be rare.)

Oh, you're right -- a cleaner construction is probably:

  foreach ($cur_inlines as $cur_inline) {
    $rows[] = $cur_inline;
  }
  // ..
}

return $rows;

The problem with this "merge rarely" is that array_merge() copies both arguments, so if we have a pathological case (say, 100 inlines) we'll copy every row 100 times (or maybe 50 times on average or whatever). Not as bad as copying every row 5000 times (or however many lines are in the file) but still not good.