Fix #279: Add support for conditional CSS classes in Html::addCssClass()

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ## 4.2.1 under development
 
-- no changes in this release.
+- New #279: Add support for conditional CSS classes in `Html::addCssClass()` (@Mister-42)
 
 ## 4.2.0 June 05, 2026
 

src/Html.php

@@ -1649,11 +1649,11 @@
                     /** @psalm-var array<array-key, scalar[]|string|Stringable|null> $value */
                     foreach ($value as $n => $v) {
                         if (!isset($v)) {
                             continue;
                         }
                         $fullName = "$name-$n";
                         if (in_array($fullName, self::ATTRIBUTES_WITH_CONCATENATED_VALUES, true)) {
                             $html .= self::renderAttribute(
                                 $fullName,
                                 self::encodeAttribute(
                                     is_array($v) ? implode(' ', $v) : $v,
@@ -1731,6 +1731,14 @@
                     $value = is_string($value->value) ? $value->value : null;
                 }
 
+                /** @psalm-suppress DocblockTypeContradiction */
+                if (is_bool($value)) {
+                    if ($value && is_string($key)) {
+                        $filteredClass[] = $key;
+                    }
+                    continue;
+                }
+
                 if ($value !== null) {
                     $filteredClass[$key] = $value;
                 }

tests/HtmlTest.php

@@ -1049,6 +1049,12 @@ public static function dataAddCssClass(): array
             16 => [['id' => 'w2', 'class' => 't1'], ['id' => 'w2'], 't1'],
             17 => [['id' => 'w2', 'class' => ['t3', 2 => 't4']], ['id' => 'w2'], ['t3', null, 't4']],
             18 => [['id' => 'w2', 'class' => ['t3', 2 => 't4']], ['id' => 'w2'], ['t3', null, 't4', null]],
+            19 => [['class' => ['btn-active']], [], ['btn-active' => true]],
+            20 => [[], [], ['btn-active' => false]],
+            21 => [['class' => ['btn', 'btn-active']], [], ['btn', 'btn-active' => true]],
+            22 => [['class' => ['btn']], [], ['btn', 'btn-active' => false]],
+            23 => [['class' => ['btn', 'btn-active']], ['class' => 'btn'], ['btn-active' => true]],
+            24 => [['class' => 'btn'], ['class' => 'btn'], ['btn-active' => false]],
         ];
     }
 
@@ -1091,6 +1097,20 @@ public function testMergeCssClass(): void
         $this->assertSame(['persistent' => 'test1', 'additional' => 'test2'], $attributes['class']);
     }
 
+    public function testAddCssClassConditional(): void
+    {
+        $attributes = ['class' => 'btn'];
+        Html::addCssClass($attributes, ['btn-active' => true, 'hidden' => false]);
+        $this->assertSame(['class' => ['btn', 'btn-active']], $attributes);
+
+        Html::addCssClass($attributes, ['btn' => true]);
+        $this->assertSame(['class' => ['btn', 'btn-active']], $attributes);
+
+        $attributes = ['class' => ['persistent' => 'widget']];
+        Html::addCssClass($attributes, ['btn', 'btn-active' => true]);
+        $this->assertSame(['class' => ['persistent' => 'widget', 'btn', 'btn-active']], $attributes);
+    }
+
     public function testAddCssClassArrayToString(): void
     {
         $attributes = ['class' => 'test'];