Magento 1.x and PHP 7 Compatibility Issue's and Solutions

As we know PHP7 is much faster than previous versions of PHP.

But there are couple of compatibility issues with magento 1.x as listed below

1. Admin login not working

Error:
Recoverable Error: session_regenerate_id(): Failed to create(read) session ID: user (path: /var/lib/php/sessions) in app/code/core/Mage/Core/Model/Session/Abstract/Varien.php on line 492

Solution: There is a issue with sessions.
This only happens when you set "session_save" in "local.xml" to "db".
If you try with the option "files" there are no problems.



2. Product Image not uploading

Error:

Fatal error</b>:  Uncaught Error: Function name must be a string in /home/admin/domains/store.com/public_html/dev/lib/Varien/File/Uploader.php:259
Stack trace:
#0 /home/admin/domains/store.com/public_html/dev/lib/Varien/File/Uploader.php(180): Varien_File_Uploader->_validateFile()
#1 /home/admin/domains/store.com/public_html/dev/app/code/core/Mage/Adminhtml/controllers/Catalog/Product/GalleryController.php(46): Varien_File_Uploader->save('/home/admin/dom...')
#2 /home/admin/domains/store.com/public_html/dev/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_Catalog_Product_GalleryController->uploadAction()
#3 /home/admin/domains/store.com/public_html/dev/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('upload')
#4 /home/admin/domains/store.com/public_html/dev/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller in /home/admin/domains/store.com/public_html/dev/lib/Varien/File/Uploader.php

Solution:  Due to uniform variable syntax the code is now interpreted strictly from left to right.

The line

$params['object']->$params['method']($this->_file['tmp_name']);
should be

$params['object']->{$params['method']}($this->_file['tmp_name']);