\Drupal\file\Plugin\rest\resource\FileUploadResource uses basename() when it needs to use the Drupal version

Looks great to me :)

Yes, we discovered this bug at #2492171: Provide options to sanitize filenames (transliterate, lowercase, replace whitespace, etc) while adding extensive test coverage for the transliterate case.
We tried to instead fix it as part of #2940383: [META] Unify file upload logic of REST and JSON:API but @wim isn't happy about that. ;)
I agree we might as well fix it here, separately, and then All The Other File Issues(tm) can stop worrying and arguing about it. ;)

Patch looks great. Simple fix. Includes a test. Note: the php bug we're solving seems to mainly impact files with an mb char at the front of the filename, which is why our previous test coverage didn't catch this.

FWIW, this applies cleanly to 8.7.x, too, and at least Drupal\Tests\file\Functional\FileUploadJsonBasicAuthTest passes locally (which is a test that uses FileUploadResourceTestBase):

 ./vendor/bin/phpunit --verbose -c core/phpunit.xml ./core/modules/file/tests/src/Functional/FileUploadJsonBasicAuthTest.php
PHPUnit 6.5.13 by Sebastian Bergmann and contributors.

Runtime:       PHP 7.2.8
Configuration: /Applications/MAMP-common/htdocs/drupal-8_7/core/phpunit.xml

Testing Drupal\Tests\file\Functional\FileUploadJsonBasicAuthTest
..........                                                        10 / 10 (100%)

Time: 3.05 minutes, Memory: 4.00MB

OK (10 tests, 151 assertions)

All that's to say: definitely RTBC. ;)

Thanks,
-Derek

Looks great, thanks for splitting this off — this now became a trivial commit :)

(This came up in #2940383-35: [META] Unify file upload logic of REST and JSON:API, I argued against expanding the scope of that issue to do this bugfix, since #2940383 is solely about moving code. If we both move and change code, it becomes really hard to review.)

I think the testbot is still recovering from all the trouble. Trying to re-upload #2 to see if this helps.

#3035320: Random fails in TimestampAgoFormatterTest and DateTimeTimeAgoFormatterTest
Re-queued #9.

Committed e1ec253 and pushed to 8.7.x. Thanks!

C/p as 0da311f4b4 and pushed to 8.6.x

🥳

Thanks for this! 👌