Test on PHP 8 and adapt resource handling

.travis.yml

@@ -2,6 +2,8 @@ language: php
 php:
   - 7.2
   - 7.3
+  - 7.4
+  - 8.0
 install:
   - composer install --no-interaction
 script:

src/GDImage.php

@@ -14,36 +14,52 @@ class GDImage
      * Constructs a new instance. Accepts either an image resource or a file
      * path to load the image from.
      *
-     * @param string|resource $value The image resource or file path.
+     * If you provide an already-loaded image resource, it is YOUR job to
+     * destroy the image when you no longer need it.
+     * Resources loaded from a file will be destroyed by this class upon calling
+     * finish().
+     *
+     * @param string|resource|\GdImage $value The image resource or file path.
      */
     public function __construct($value)
     {
-        if (!is_resource($value)) {
-            $value = imagecreatefromstring(file_get_contents($value));
-            $this->destroy = true;
+        // PHP < 8 uses resources, PHP >= 8 uses GdImage objects.
+        if (is_resource($value) || $value instanceof \GdImage) {
+            $this->res = $value;
+            return;
         }
-        $this->res = $value;
+        $this->res = imagecreatefromstring(file_get_contents($value));
+        $this->destroy = true;
     }
 
     /**
-     * @return resource The underlying GD image resource.
+     * Disposes of this image by calling `finish()`.
      */
-    public function getResource()
+    public function __destruct()
     {
-        return $this->res;
+        $this->finish();
     }
 
     /**
-     * Frees the allocated resource if it was loaded in the constructor. Will
-     * not free the resource if it was passed already-loaded.
+     * Free any allocated resources. This should be called as soon as the image
+     * is no longer needed.
      *
      * @return void
      */
     public function finish()
     {
-        if ($this->destroy) {
+        if ($this->destroy && isset($this->res)) {
             imagedestroy($this->res);
         }
+        $this->res = null;
+    }
+
+    /**
+     * @return resource The underlying GD image resource.
+     */
+    public function getResource()
+    {
+        return $this->res;
     }
 
     /**

tests/GDImageTest.php

@@ -59,11 +59,17 @@ public function testFinish()
         $obj = new GDImage('./tests/images/stripes-bw-10x10.png');
         $img = $obj->getResource();
         $obj->finish();
-        try {
-            imagesx($img);
-        } catch (Exception $e) {
-            return;
+        // skip on PHP >= 8, where images are objects instead of resources
+        // and where manual destruction does nothing
+        if (is_resource($img)) {
+            // expect resource to be destroyed
+            try {
+                imagesx($img);
+            } catch (Exception $e) {
+                return;
+            }
+            $this->fail();
         }
-        $this->fail();
+        $this->assertNull($obj->getResource());
     }
 }