Adapt some non-breaking changes from the master branch

Signed-off-by: Jack Cherng <jfcherng@gmail.com>

Author: jfcherng

src/Diff.php

@@ -21,7 +21,8 @@ final class Diff
      * @var array cached properties and their default values
      */
     private const CACHED_PROPERTIES = [
-        'groupedCodes' => null,
+        'groupedOpcodes' => [],
+        'oldNewComparison' => 0,
     ];
 
     /**
@@ -45,14 +46,20 @@ final class Diff
     private $isCacheDirty = true;
 
     /**
-     * @var null|SequenceMatcher the sequence matcher
+     * @var SequenceMatcher the sequence matcher
      */
     private $sequenceMatcher;
 
     /**
-     * @var null|array array containing the generated opcodes for the differences between the two items
+     * @var int the result of comparing the old and the new with the spaceship operator
+     *          -1 means old < new, 0 means old == new, 1 means old > new
      */
-    private $groupedCodes;
+    private $oldNewComparison = 0;
+
+    /**
+     * @var array array containing the generated opcodes for the differences between the two items
+     */
+    private $groupedOpcodes = [];
 
     /**
      * @var array associative array of the default options available for the diff class and their default value
@@ -186,6 +193,16 @@ public function getOptions(): array
         return $this->options;
     }
 
+    /**
+     * Compare the old and the new with the spaceship operator.
+     *
+     * @return int
+     */
+    public function getOldNewComparison(): int
+    {
+        return $this->oldNewComparison;
+    }
+
     /**
      * Get the singleton.
      *
@@ -210,8 +227,12 @@ public function getGroupedOpcodes(): array
     {
         $this->finalize();
 
-        return $this->groupedCodes = $this->groupedCodes ??
-            $this->sequenceMatcher->getGroupedOpcodes($this->options['context']);
+        if (!empty($this->groupedOpcodes)) {
+            return $this->groupedOpcodes;
+        }
+
+        return $this->groupedOpcodes = $this->sequenceMatcher
+            ->getGroupedOpcodes($this->options['context']);
     }
 
     /**
@@ -228,8 +249,7 @@ public function render(AbstractRenderer $renderer): string
         $renderer->setDiff($this);
 
         // the "no difference" situation may happen frequently
-        // let's save some calculation if possible
-        return $this->old === $this->new
+        return $this->oldNewComparison === 0
             ? $renderer::getIdenticalResult()
             : $renderer->render();
     }
@@ -326,6 +346,8 @@ private function finalize(): self
         if ($this->isCacheDirty) {
             $this->resetCachedResults();
 
+            $this->oldNewComparison = $this->old <=> $this->new;
+
             $this->sequenceMatcher
                 ->setOptions($this->options)
                 ->setSequences($this->old, $this->new);

src/Renderer/Html/AbstractHtml.php

@@ -46,9 +46,6 @@ public function getChanges(): array
             $this->options
         );
 
-        // As we'll be modifying old & new to include our change markers,
-        // we need to get the contents and store them here. That way
-        // we're not going to destroy the original data
         $old = $this->diff->getOld();
         $new = $this->diff->getNew();