#121 Magento2.Templates.HelperInTemplate Rule porposal

Magento2/Sniffs/Templates/HelperInTemplateSniff.md

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+# Rule: Do not use `helpers` in templates
+## Background
+The use of helpers is in general discouraged. Consider using a ViewModel instead.
+
+## Reasoning
+The use of helpers is in general discouraged therefore any `$this->helper(<helper_class>)` code used in PHTML templates should be refactored.
+
+Consider using ViewModel instead.
+
+## How to fix
+
+Typical example of a helper being used in a PHTML:
+```html
+<?php $_incl = $block->helper(<helper_class>)->...; ?>
+```
+
+Once the ViewModel is created, call it in the PHTML as follow:
+
+```html
+<?php $viewModel = $block->getViewModel(); ?>
+```
+or
+```html
+<?php $viewModel = $block->getData('viewModel'); ?>
+```

Magento2/Sniffs/Templates/HelperInTemplateSniff.php

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+<?php
+/**
+ * Copyright © Magento. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+namespace Magento2\Sniffs\Templates;
+
+use PHP_CodeSniffer\Sniffs\Sniff;
+use PHP_CodeSniffer\Files\File;
+
+/**
+ * Detects possible usage of helper in templates.
+ */
+class HelperInTemplateSniff implements Sniff
+{
+    /**
+     * String representation of warning.
+     *
+     * @var string
+     */
+    protected $warningMessage = 'Usage of helpers in templates is discouraged.';
+
+    /**
+     * Warning violation code.
+     *
+     * @var string
+     */
+    protected $warningCode = 'FoundThis';
+
+    /**
+     * @inheritdoc
+     */
+    public function register()
+    {
+        return [T_VARIABLE];
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function process(File $phpcsFile, $stackPtr)
+    {
+        $tokens = $phpcsFile->getTokens();
+        if ($tokens[$stackPtr]['content'] === 'helper(') {
+            $phpcsFile->addWarning($this->warningMessage, $stackPtr, $this->warningCode);
+        }
+    }
+}