Drupal 9 Deprecated Code Report

The patch applies cleanly:

martin@martin-XPS-13-9370 /var/www/html/brown.localhost/web/modules/tablefield (8.x-2.x=) $ git apply -v drupal_9_deprecated_code_report-3062227-2.patch
Checking patch src/Element/Tablefield.php...
Hunk #1 succeeded at 274 (offset 1 line).
Hunk #2 succeeded at 309 (offset 1 line).
Hunk #3 succeeded at 345 (offset 11 lines).
Checking patch src/Form/TablefieldConfigForm.php...
Applied patch src/Element/Tablefield.php cleanly.
Applied patch src/Form/TablefieldConfigForm.php cleanly.

Patch solves the errors:

martin@martin-XPS-13-9370 /var/www/html/brown.localhost/web/modules $ drupal-check tablefield
 12/12 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%

 [OK] No errors                                                                                                         

Manual test to trigger the changed code to check correct functionality BEFORE and AFTER the patch:

• At node/1/edit CHANGE NUMBER OF ROWS/COLUMNS should result in status (green) message "Table structure rebuilt.". BEFORE: OK, AFTER: OK
• At node/1/edit IMPORT FROM CSV when uploading a non-CSV file should result in error (red) message "Only files with the following extensions are allowed: csv.". BEFORE: OK, AFTER: OK
• At node/1/edit IMPORT FROM CSV when uploading a CSV file should result in status (green) message "Successfully imported some-file.csv: csv.". BEFORE: OK, AFTER: OK

At admin/config/content/tablefield "CSV separator" that must be one character only cannot be tested as on the form '#maxlength' => 1,. We believe that validation on it can be removed. As it was present also before, it is no blocker for committing the patch though.

Related Change record:
drupal_get_message() and drupal_set_message() replaced by Messenger service | Drupal.org

API:
MessengerInterface | MessengerInterface.php | Drupal 8.7.x | Drupal API

Looking at 8 - Best practice: $this->t() versus t() - Drupal Answers it seems we should rather use $this->t(). As is was already there, this is also no blocker. Opening new issues for the findings.

Added some follow-up issues.

Thanks for your contribution,

Seems that not all PHP version support this yet out-of-the-box.

Error: Call to undefined method Drupal\Component\Utility\Unicode::mb_strlen() in Drupal\tablefield\Form\TablefieldConfigForm->validateForm() (line 76 of /var/www/html/brown.localhost/web/modules/tablefield/src/Form/TablefieldConfigForm.php)

Drupal Version
8.7.3

PHP
Version
7.2.19-1+ubuntu18.04.1+deb.sury.org+1

But it seems normal that the extension might be needed to be added:
php - Fatal error: Call to undefined function mb_strlen() - Stack Overflow

The #7 error will not occur anymore as the validation function has been removed in #3064974: Unnecessary validation function. Thanks.