Fix error messages not being displayed with nested input elements.

The error message element is not being displayed when it's not a sibling
of an (input) element with an `is-invalid` class, which is the case for:

* Input groups
* Horizontally aligned checkboxes
* Custom file controls

src/View/Helper/FormHelper.php

@@ -89,10 +89,10 @@ class FormHelper extends Helper
         'multicheckboxWrapper' => '<fieldset class="form-group">{{content}}</fieldset>',
         'multicheckboxTitle' => '<legend class="col-form-label pt-0">{{text}}</legend>',
         'customFileLabel' => '<label class="custom-file-label"{{attrs}}>{{text}}{{tooltip}}</label>',
-        'customFileFormGroup' => '<div class="custom-file">{{input}}{{label}}</div>',
+        'customFileFormGroup' => '<div class="custom-file {{invalid}}">{{input}}{{label}}</div>',
         'customFileInputGroupFormGroup' => '{{input}}',
-        'customFileInputGroupContainer' => '<div{{attrs}}>{{prepend}}<div class="custom-file">{{content}}{{label}}' .
-            '</div>{{append}}</div>',
+        'customFileInputGroupContainer' =>
+            '<div{{attrs}}>{{prepend}}<div class="custom-file {{invalid}}">{{content}}{{label}}</div>{{append}}</div>',
         'nestingLabel' => '{{hidden}}{{input}}<label{{attrs}}>{{text}}{{tooltip}}</label>',
         'nestingLabelNestedInput' => '{{hidden}}<label{{attrs}}>{{input}}{{text}}{{tooltip}}</label>',
     ];
@@ -127,13 +127,13 @@ class FormHelper extends Helper
             'label' => '<label class="col-form-label %s"{{attrs}}>{{text}}{{tooltip}}</label>',
             'fileLabel' => '<label class="col-form-label pt-1 %s"{{attrs}}>{{text}}{{tooltip}}</label>',
             'formGroup' => '{{label}}<div class="%s">{{input}}{{error}}{{help}}</div>',
-            'customFileFormGroup' => '<div class="%s"><div class="custom-file">{{input}}{{label}}</div>' .
-                    '{{error}}{{help}}</div>',
+            'customFileFormGroup' =>
+                '<div class="%s"><div class="custom-file {{invalid}}">{{input}}{{label}}</div>{{error}}{{help}}</div>',
             'customFileInputGroupFormGroup' => '<div class="%s">{{input}}{{error}}{{help}}</div>',
-            'checkboxFormGroup' => '<div class="%s"><div class="form-check">{{input}}{{label}}</div>' .
-                    '{{error}}{{help}}</div>',
+            'checkboxFormGroup' =>
+                '<div class="%s"><div class="form-check">{{input}}{{label}}{{error}}{{help}}</div></div>',
             'customCheckboxFormGroup' => '<div class="%s"><div class="custom-control custom-checkbox">' .
-                    '{{input}}{{label}}</div>{{error}}{{help}}</div>',
+                    '{{input}}{{label}}{{error}}{{help}}</div></div>',
             'datetimeContainer' => '<div class="form-group row {{type}}{{required}}" role="group" ' .
                     'aria-labelledby="{{groupId}}">{{content}}</div>',
             'datetimeContainerError' => '<div class="form-group row {{type}}{{required}} is-invalid" ' .
@@ -450,6 +450,10 @@ public function control(string $fieldName, array $options = []): string
                     $options['templates']['label'] = $this->templater()->get('customFileLabel');
                     $options['templates']['formGroup'] = $this->templater()->get('customFileFormGroup');
 
+                    if ($this->_getContext()->hasError($fieldName)) {
+                        $options['templateVars']['invalid'] = $this->_config['errorClass'];
+                    }
+
                     if (
                         $options['prepend'] ||
                         $options['append']
@@ -512,6 +516,13 @@ public function control(string $fieldName, array $options = []): string
             unset($options['tooltip']);
         }
 
+        if (
+            isset($options['append']) ||
+            isset($options['prepend'])
+        ) {
+            $options['injectErrorClass'] = $this->_config['errorClass'];
+        }
+
         $result = parent::control($fieldName, $options);
 
         if ($newTemplates) {

src/View/Widget/InputgroupTrait.php

@@ -33,6 +33,7 @@ protected function _withInputGroup(array $data, ContextInterface $context): stri
             'prepend' => null,
             'append' => null,
             'injectFormControl' => true,
+            'injectErrorClass' => null,
             'input' => null,
         ];
 
@@ -42,7 +43,8 @@ protected function _withInputGroup(array $data, ContextInterface $context): stri
 
         $prepend = $data['prepend'];
         $append = $data['append'];
-        unset($data['append'], $data['prepend'], $data['injectFormControl']);
+        $errorClass = $data['injectErrorClass'];
+        unset($data['append'], $data['prepend'], $data['injectFormControl'], $data['injectErrorClass']);
 
         if (isset($data['input'])) {
             $input = $data['input'];
@@ -68,6 +70,13 @@ protected function _withInputGroup(array $data, ContextInterface $context): stri
         }
 
         if ($prepend || $append) {
+            if (
+                $errorClass &&
+                $context->hasError($data['fieldName'])
+            ) {
+                $attrs['class'][] = $errorClass;
+            }
+
             $input = $this->_templates->format('inputGroupContainer', [
                 'attrs' => $this->_templates->formatAttributes($attrs),
                 'append' => $append,