careful treatment of string PHPExcel in migrator

src/PhpSpreadsheet/Helper/Migrator.php

@@ -204,7 +204,6 @@ public function getMapping()
             'PHPExcel_Settings' => \PhpOffice\PhpSpreadsheet\Settings::class,
             'PHPExcel_Style' => \PhpOffice\PhpSpreadsheet\Style\Style::class,
             'PHPExcel_Worksheet' => \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet::class,
-            'PHPExcel' => \PhpOffice\PhpSpreadsheet\Spreadsheet::class,
         ];
 
         $methods = [
@@ -266,12 +265,16 @@ private function recursiveReplace($path)
             foreach (glob($path . $pattern) as $file) {
                 if (strpos($path, '/vendor/') !== false) {
                     echo $file . " skipped\n";
-
                     continue;
                 }
                 $original = file_get_contents($file);
                 $converted = str_replace($from, $to, $original);
 
+                // The string "PHPExcel" gets special treatment because of how common it might be.
+                // This regex requires a word boundary around the string, and it can't be
+                // preceded by $ or -> (goal is to filter out cases where a variable is named $PHPExcel or similar)
+                $converted = preg_replace('/(?<!\$|->)\bPHPExcel\b/', \PhpOffice\PhpSpreadsheet\Spreadsheet::class, $original);
+
                 if ($original !== $converted) {
                     echo $file . " converted\n";
                     file_put_contents($file, $converted);