Unset _style during encode/decode of backend packets to avoid type mismatch errors

[q0rban]

If a drush command uses a Robo collection (or perhaps just a Robo task—untested), and that command is invoked as a backend process, and that command fails, you may see an error like this:

 [error]  Drush command terminated abnormally due to an unrecoverable error.
Error: Uncaught Error: Unsupported operand types in /app/vendor/consolidation/log/src/LogOutputStyler.php:66
Stack trace:
#0 /app/vendor/consolidation/log/src/Logger.php(186): Consolidation\Log\LogOutputStyler->style(Array)
#1 /app/vendor/consolidation/log/src/Logger.php(171): Consolidation\Log\Logger->doLog(Object(Symfony\Component\Console\Output\StreamOutput), 'error', '', Array)
#2 /app/vendor/drush/drush/src/Log/Logger.php(174): Consolidation\Log\Logger->log('error', '', Array)
#3 /app/vendor/drush/drush/includes/drush.inc(454): Drush\Log\Logger->log('error', '', Array)
#4 /app/vendor/drush/drush/includes/drush.inc(428): _drush_log_to_logger(Object(Drush\Log\Logger), Array)
#5 /app/vendor/drush/drush/includes/drush.inc(488): _drush_log(Array)
#6 /app/vendor/drush/drush/includes/backend.inc(542): drush_backend_packet_log(Array, Array)
#7 /app/vendor/drush/drush/includes/backend.inc(454): drush_backend_parse_packets('\x00DRUSH_BACKEND:...', '', Array)
#8 /app/vendor/drush/drush/includes/backend.inc(1040): _drush_b in /app/vendor/consolidation/log/src/LogOutputStyler.php, line 66

After some debugging, it turns out this is because Robo\Log\ResultPrinter sets ['_style']['message'] to an empty string, which then gets encoded to json. When the "frontend" process then decodes this json, ['_style'] is decoded as a stdClass. This subsequently results in an unsupported operand error in Consolidation\Log\LogOutputStyler::style() as that function expects _style to be an array.

The attached patch strips _style from the packet prior to encoded and subsequent to decoding. You may wonder why the latter is necessary if the former is done, but remember that different versions of drush may be involved, so an older version of drush may happily send along the _style and recreate the same error on a newer version of drush. Cleaning up in both places should avoid this possibility.

[greg-1-anderson]

LGTM

[greg-1-anderson]

Needs test failure fixed, though. Not sure why it's failing; removal of style somehow affected linebreaks maybe?

[weitzman]

I saw a similar failure in another PR so I dont think its caused by the change here.

[greg-1-anderson]

Test failure must be intermittent; I re-ran the workflow and it passed.