[FEATURE] Convert legacy color notation to modern css 4 notation

CHANGELOG.md

@@ -39,6 +39,12 @@ Please also have a look at our
 
 ### Documentation
 
+## 9.2.0:
+
+### Added
+
+- Add use modern CSS color syntax option to `OutputFormat` (#1442)
+
 ## 9.1.0: Add support for PHP 8.5
 
 ### Added

src/OutputFormat.php

@@ -20,6 +20,13 @@ final class OutputFormat
      */
     private $usesRgbHashNotation = true;
 
+    /**
+     * Output RGB colors in CSS 4 notation if possible
+     *
+     * @var bool
+     */
+    private $usesModernColorSyntax = false;
+
     /**
      * Declaration format
      *
@@ -220,6 +227,24 @@ public function setRGBHashNotation(bool $usesRgbHashNotation): self
         return $this;
     }
 
+    /**
+     * @internal
+     */
+    public function usesModernColorSyntax(): bool
+    {
+        return $this->usesModernColorSyntax;
+    }
+
+    /**
+     * @return $this fluent interface
+     */
+    public function setUseModernColorSyntax(bool $usesModernColorSyntax): self
+    {
+        $this->usesModernColorSyntax = $usesModernColorSyntax;
+
+        return $this;
+    }
+
     /**
      * @internal
      */

src/Value/Color.php

@@ -232,7 +232,7 @@ public function render(OutputFormat $outputFormat): string
             return $this->renderAsHex();
         }
 
-        if ($this->shouldRenderInModernSyntax()) {
+        if ($this->shouldRenderInModernSyntax($outputFormat)) {
             return $this->renderInModernSyntax($outputFormat);
         }
 
@@ -309,9 +309,9 @@ private function renderAsHex(): string
      *     The same in the CSS Color Module Level 4 W3C Candidate Recommendation Draft
      *   } (as of 13 February 2024, at time of writing).
      */
-    private function shouldRenderInModernSyntax(): bool
+    private function shouldRenderInModernSyntax(OutputFormat $outputFormat): bool
     {
-        if ($this->hasNoneAsComponentValue()) {
+        if ($this->hasNoneAsComponentValue() || $outputFormat->usesModernColorSyntax()) {
             return true;
         }
 
@@ -385,6 +385,12 @@ private function renderInModernSyntax(OutputFormat $outputFormat): string
             $arguments = $formatter->implode($separator, [$arguments, $alpha]);
         }
 
-        return $this->getName() . '(' . $arguments . ')';
+        $name = $this->getName();
+
+        if ($outputFormat->usesModernColorSyntax()) {
+            $name = str_replace('a', '', $name);
+        }
+
+        return $name . '(' . $arguments . ')';
     }
 }