Add validation constraints to core.entity_form_mode.*.*

Problem/Motivation

Form modes have 3 property paths that are not yet validatable:

vendor/bin/drush config:inspect --filter-keys=core.entity_form_mode.user.register --detail --list-constraints
➜  🤖 Analyzing…

 Legend for Data: 
  ✅❓  → Correct primitive type, detailed validation impossible.
  ✅✅  → Correct primitive type, passed all validation constraints.
 ---------------------------------------------------------------- --------- ------------- ------ --------------------------------------------------------------------------------------------- 
  Key                                                              Status    Validatable   Data   Validation constraints                                                                       
 ---------------------------------------------------------------- --------- ------------- ------ --------------------------------------------------------------------------------------------- 
  core.entity_form_mode.user.register                              Correct   79%           ✅❓   ValidKeys: '<infer>'                                                                         
   core.entity_form_mode.user.register:                            Correct   Validatable   ✅✅   ValidKeys: '<infer>'                                                                         
   core.entity_form_mode.user.register:_core                       Correct   Validatable   ✅✅   ValidKeys:                                                                                   
                                                                                                    - default_config_hash                                                                      
   core.entity_form_mode.user.register:_core.default_config_hash   Correct   Validatable   ✅✅   NotNull: {  }                                                                                
                                                                                                  Regex: '/^[a-zA-Z0-9\-_]+$/'                                                                 
                                                                                                  Length: 43                                                                                   
                                                                                                  ↣ PrimitiveType: {  }                                                                        
   core.entity_form_mode.user.register:cache                       Correct   Validatable   ✅✅   ↣ PrimitiveType: {  }                                                                        
   core.entity_form_mode.user.register:dependencies                Correct   Validatable   ✅✅   ValidKeys: '<infer>'                                                                         
   core.entity_form_mode.user.register:dependencies.module         Correct   NOT           ✅❓   ❌ @todo Add validation constraints to ancestor type: config_dependencies                    
   core.entity_form_mode.user.register:dependencies.module.0       Correct   Validatable   ✅✅   NotBlank: {  }                                                                               
                                                                                                  ExtensionName: {  }                                                                          
                                                                                                  ExtensionExists: module                                                                      
                                                                                                  ↣ PrimitiveType: {  }                                                                        
   core.entity_form_mode.user.register:description                 Correct   Validatable   ✅✅   Regex:                                                                                       
                                                                                                    pattern: '/([^\PC\x09\x0a\x0d])/u'                                                         
                                                                                                    match: false                                                                               
                                                                                                    message: 'Text is not allowed to contain control characters, only visible characters.'     
                                                                                                  ↣ PrimitiveType: {  }                                                                        
   core.entity_form_mode.user.register:id                          Correct   NOT           ✅❓   ⚠️  @todo Add validation constraints to config entity type: core.entity_form_mode.*.*        
   core.entity_form_mode.user.register:label                       Correct   Validatable   ✅✅   Regex:                                                                                       
                                                                                                    pattern: '/([^\PC])/u'                                                                     
                                                                                                    match: false                                                                               
                                                                                                    message: 'Labels are not allowed to span multiple lines or contain control characters.'    
                                                                                                  NotBlank: {  }                                                                               
                                                                                                  ↣ PrimitiveType: {  }                                                                        
   core.entity_form_mode.user.register:langcode                    Correct   Validatable   ✅✅   NotNull: {  }                                                                                
                                                                                                  Choice:                                                                                      
                                                                                                    callback: 'Drupal\Core\TypedData\Plugin\DataType\LanguageReference::getAllValidLangcodes'  
                                                                                                  ↣ PrimitiveType: {  }                                                                        
   core.entity_form_mode.user.register:status                      Correct   Validatable   ✅✅   ↣ PrimitiveType: {  }                                                                        
   core.entity_form_mode.user.register:targetEntityType            Correct   NOT           ✅❓   ⚠️  @todo Add validation constraints to config entity type: core.entity_form_mode.*.*        
   core.entity_form_mode.user.register:uuid                        Correct   Validatable   ✅✅   Uuid: {  }                                                                                   
                                                                                                  ↣ PrimitiveType: {  }                                                                        
 ---------------------------------------------------------------- --------- ------------- ------ --------------------------------------------------------------------------------------------- 

Steps to reproduce

1. Get a local git clone of Drupal core 11.x.
2. composer require drupal/config_inspector — or manually install https://www.drupal.org/project/config_inspector/releases/2.1.5 or newer (which supports Drupal 11!)
3. composer require drush/drush
4. vendor/bin/drush config:inspect --filter-keys=core.entity_form_mode.user.register --detail --list-constraints

Proposed resolution

Add validation constraints to:

1. core.entity_form_mode.*.*:dependencies.module
2. core.entity_form_mode.*.*:id
3. core.entity_form_mode.*.*:targetEntityType

This requires looking at the existing code and admin UI (if any) to understand which values could be considered valid. Eventually this needs to be reviewed by the relevant subsystem maintainer.

For examples, search *.schema.yml files for the string constraints: 😊

Reach out to @borisson_ or @wimleers in the #distributions-and-recipes.

Remaining tasks

User interface changes

None.

API changes

None.

Data model changes

More validation 🚀

Release notes snippet

None.