Migration from D7 to D9.

Tested manually and added my observations below:

1. +++ b/maxlength.module
   @@ -176,3 +179,65 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +    function ($definition) {
   +      return $definition['id'] === 'd7_field_instance_widget_settings';
   +    }
   +  );
   +
   +  foreach (array_keys($field_instance_widget_settings_migrations) as $plugin_id) {
   

   Check if Maxlength module is enabled on the source site or not.

2. +++ b/maxlength.module
   @@ -176,3 +179,65 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +  $unserialised_data = unserialize($row->getSourceProperty('data'));
   

   What if $row->getSourceProperty('data') does not have any value?

3. +++ b/maxlength.module
   @@ -176,3 +179,65 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +  if (array_key_exists("maxlength_js", $unserialised_data)) {
   +
   +    switch ($row->getSourceProperty('field_definition')['type']) {
   

   Extra space

4. +++ b/maxlength.module
   @@ -176,3 +179,65 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +      case 'text':
   +        $maxlength_config['maxlength_js'] = unserialize($row->getSourceProperty('field_definition')['data'])['settings']['max_length'];
   +        $maxlength_config['maxlength_js_label'] = $unserialised_data['maxlength_js_label'];
   +        break;
   +
   +      case 'text_long':
   

   Title and link migration missing.
   To reproduce link migration issue enable https://www.drupal.org/project/link

5. +++ b/maxlength.module
   @@ -176,3 +179,65 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +        $maxlength_config['maxlength_js_label'] = $unserialised_data['maxlength_js_label'];
   

   Common data can be moved above switch case.

6. +++ b/maxlength.module
   @@ -176,3 +179,65 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +
   

   Remove extra space wherever possible.

7. +++ b/tests/fixtures/drupal7.php
   @@ -0,0 +1,22 @@
   +include 'drupal7' . DIRECTORY_SEPARATOR . 'node.php';
   +include 'drupal7' . DIRECTORY_SEPARATOR . 'node_comment_statistics.php';
   

   Seems irrelevant to me.

8. +++ b/tests/src/Kernel/MaxlengthMigrationTest.php
   @@ -0,0 +1,151 @@
   +  protected static $configSchemaCheckerExclusions = [
   +    'core.entity_form_display.comment.comment_node_article.default',
   +    'core.entity_form_display.node.article.default',
   +    'core.entity_form_display.node.page.default',
   +    'core.entity_form_display.node.webform.default',
   +    'core.entity_form_display.user.user.default',
   +    'core.entity_form_display.taxonomy_term.some_tax.default',
   +  ];
   

   Do we require this in this case?

9. +++ b/tests/src/Kernel/MaxlengthMigrationTest.php
   @@ -0,0 +1,151 @@
   +  protected function setUp() {
   +    // @todo Change the autogenerated stub
   +    parent::setUp();
   +    $this->installConfig(['node']);
   +    $this->installEntitySchema('node');
   +    $this->installConfig(['comment']);
   +    $this->installEntitySchema('comment');
   +  }
   

   Is it required in this case?

1. +++ b/maxlength.module
   @@ -176,3 +181,91 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +  $unserialised_data = $row->getSourceProperty('widget')['settings'];
   +  $maxlength_config = [];
   +  if ($row->getSourceProperty('field_definition')['type'] === 'link_field') {
   

   Title field maxlength configurations are still not migrated.

2. +++ b/maxlength.module
   @@ -176,3 +181,91 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +        $maxlength_config['maxlength_js_label'] = $unserialised_data['maxlength_js_label'];
   

   This line can be added outside switch case.

3. +++ b/tests/fixtures/drupal7.php
   @@ -0,0 +1,20 @@
   +include 'drupal7' . DIRECTORY_SEPARATOR . 'comment.php';
   

   This is not required.

Re #11: Very nice job, I've only a few minor nits.

1. +++ b/maxlength.module
   @@ -176,3 +181,89 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +/**
   + * Implements hook_migrate_prepare_row().
   + *
   + * Alters maxlength config before being pushed into
   + * d7_field_instance_widget_settings.
   + */
   +function maxlength_migrate_prepare_row(Row $row, MigrateSourceInterface $source, MigrationInterface $migration) {
   +  if ($migration->getBaseId() !== 'd7_field_instance_widget_settings' || !in_array('maxlength', $migration->getMigrationTags())) {
   +    return;
   +  }
   

   It is enough to check whether the maxlength migration tag is present or not.

2. +++ b/maxlength.module
   @@ -176,3 +181,89 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +  $unserialised_data = $row->getSourceProperty('widget')['settings'];
   

   This reads better if you write $row->getSourceProperty('widget/settings').
   In addition, the name of the variable should refer to the data in it, e.g. $widget_settings

3. +++ b/maxlength.module
   @@ -176,3 +181,89 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +  if ($row->getSourceProperty('field_definition')['type'] === 'link_field') {
   ...
   +    switch ($row->getSourceProperty('field_definition')['type']) {
   

   The data in field_definition/type is the same what is already available in the type source property (it is the field type).

4. +++ b/maxlength.module
   @@ -176,3 +181,89 @@ function maxlength_field_widget_form_alter(&$element, FormStateInterface $form_s
   +  if (array_key_exists("maxlength_js", $unserialised_data)) {
   ...
   +  else {
   +    $row->setSourceProperty('maxlength_config', NULL);
   +  }
   

   We don't have to do anything if the array key does not exist (I mean you don't need the else statement at all). And other than that, if $unserialized_data['maxlength_js'] is 0, then there is no limitation, so we shouldn't migrate any maxlength configuration.

   With these in mind, I would say just use an early return:

   if (empty($var['maxlength_js']) {
     return;
   }
   

5. +++ b/migrations/d7_maxlength_title_settings.yml
   @@ -0,0 +1,24 @@
   +migration_dependencies:
   +  required:
   +    - d7_node_type
   

   It would be nice to provide an optional support for the core patch at #3097336: Improve the DX for migrating content entities: view modes, fields, formatters, widgets etc should be migrated per entity type + bundle.

6. +++ b/src/Plugin/migrate/source/Maxlength.php
   @@ -0,0 +1,63 @@
   +    if (!empty($this->configuration["node_type"])) {
   +      $query->condition('name', 'maxlength_js_label_' . $this->configuration["node_type"]);
   

   Please prefer single quotes where possible!
   https://www.drupal.org/docs/develop/standards/coding-standards#quotes

7. +++ b/tests/src/Kernel/MaxlengthMigrationTest.php
   @@ -0,0 +1,161 @@
   +/**
   + * Tests D7 maxlength migration plugin.
   + *
   + * @group maxlength
   + */
   +class MaxlengthMigrationTest extends MigrateDrupal7TestBase {
   +  /**
   

   An empty line is missing at the beginning of this test class' body (after the opening curly brace).

+++ b/src/Plugin/migrate/MaxlengthDeriver.php
@@ -0,0 +1,48 @@
+        $derivative_definition['migration_dependencies']['required'] = ['d7_node_type:' . $node_type];

The d7_node_type migration isn't a derived migration in Drupal core; the thing what makes it available is the patch at #3097336: Improve the DX for migrating content entities: view modes, fields, formatters, widgets etc should be migrated per entity type + bundle.

By default, the node label max length migrations should depend on d7_node_type. But if the patch in 3097336 is applied, then these migration should (and can) depend on the corresponding d7_node_type derivative.

Edit: I was wrong. You can ignore my concern at #12.5.

#16 deserves RTBC.

Thank you, @omkar.podey, great work!

After may months in use, not a single problem reported.

Thank you for the good work, omkar, for the review and feedback, huzooka, and for the prodding, Wim! Committing this to the project.

Alas, I spoke to soon -- I just caught that there is a coding standards issue w/ line 263:

      $maxlength_config['maxlength_js'] = unserialize($row->getSourceProperty('field_definition')['data'])['settings']['max_length']

unserialize() is insecure unless allowed classes are limited. Use a safe format like JSON or use the allowed_classes option.
(DrupalPractice.FunctionCalls.InsecureUnserialize.InsecureUnserialize)

I'll work on it.

Could someone review it, please.

Hi, I will review it.

Thanks, @Adaucyj, for the patch, it fixes the last CS issue.
Moving to RTBC.

Marking as needs review to check if anything needs updating to make it work with the 2.1.x branch.