Check for correct whitespace in method declarations

This completes other existing Sniffs that already are doing
the job partially:
- Squiz.Whitespace.ScopeKeywordSpacing (for visibility and static).
- PSR2.Methods.MethodDeclaration (for ordering).

What we are doing here is:
- Add the following Sniffs to verify that he return type is
  being used correctly (space-wise):
   - PSR12.Functions.ReturnTypeDeclaration
   - PSR12.Functions.NullableTypeDeclaration
- Create a new own Sniff: MethodDeclarationSpacingSniff that is
  in charge of checking all the remaining bits:
   - 1 exact space after "abstract" and "final".
   - 1 exact space after "function".
   - 0 spaces after the function name.
   - 0 spaces after the function open parenthesis.

With everything enabled, we'll get something like this:
```
<     final    abstract     protected static function     kk    ( $a, $b, $c  )   :?  int  {
---
>     final abstract protected static function kk($a, $b, $c  ): ?int {
```

Fixes #99

moodle/Sniffs/Methods/MethodDeclarationSpacingSniff.php

@@ -0,0 +1,170 @@
+<?php
+// This file is part of Moodle - https://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <https://www.gnu.org/licenses/>.
+
+/**
+ * This sniff checks that method declarations are correct, spacing-wise.
+ *
+ * This Sniff completes other Sniffs, already included in the moodle standard,
+ * to ensure that the methods declarations make a correct use of whitespace.
+ * More specifically, it completes the following:
+ * - PSR12.Functions.ReturnTypeDeclaration
+ * - PSR12.Functions.NullableTypeDeclaration
+ * - PSR2.Methods.MethodDeclaration
+ * - Squiz.Whitespace.ScopeKeywordSpacing
+ *
+ * If any of the above Sniffs is disabled, then we'll have to add more
+ * features to this one.
+
+ * @copyright 2024 onwards Eloy Lafuente (stronk7) {@link https://stronk7.com}
+ * @license   https://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace MoodleHQ\MoodleCS\moodle\Sniffs\Methods;
+
+use PHP_CodeSniffer\Files\File;
+use PHP_CodeSniffer\Sniffs\AbstractScopeSniff;
+use PHP_CodeSniffer\Util\Tokens;
+
+class MethodDeclarationSpacingSniff extends AbstractScopeSniff
+{
+    public function __construct() {
+        parent::__construct(Tokens::$ooScopeTokens, [T_FUNCTION]);
+    }
+
+    /**
+     * Processes the function tokens within the class.
+     *
+     * @param File $file The file where this token was found.
+     * @param int $stackPtr  The position where the token was found.
+     * @param int $currScope The current scope opener token.
+     *
+     * @return void
+     */
+    protected function processTokenWithinScope(File $file, $stackPtr, $currScope)
+    {
+        // List of tokens that require one space after them.
+        $oneSpaceTokens = [
+            // T_PUBLIC,    // Disabled. Squiz.WhiteSpace.ScopeKeywordSpacing handles it.
+            // T_PROTECTED, // Disabled. Squiz.WhiteSpace.ScopeKeywordSpacing handles it.
+            // T_PRIVATE,   // Disabled. Squiz.WhiteSpace.ScopeKeywordSpacing handles it.
+            // T_STATIC,    // Disabled. Squiz.WhiteSpace.ScopeKeywordSpacing handles it.
+            T_ABSTRACT,
+            T_FINAL,
+            T_FUNCTION,
+        ];
+
+        // List of tokens that require no space after them.
+        $noSpaceTokens = [
+            T_STRING,
+            T_OPEN_PARENTHESIS,
+        ];
+
+        $tokens = $file->getTokens();
+
+        // Determine if this is a function which needs to be examined.
+        $conditions = $tokens[$stackPtr]['conditions'];
+        end($conditions);
+        $deepestScope = key($conditions);
+        if ($deepestScope !== $currScope) {
+            return;
+        }
+
+        $methodName = $file->getDeclarationName($stackPtr);
+        if ($methodName === null) {
+            // Ignore closures.
+            return;
+        }
+
+        // Find the opening parenthesis of the argument list. That's the last token
+        // that this Sniff is interested in. If, for any reason, the opening parenthesis
+        // is not found, then we'll start from current T_FUNCTION token.
+        $lastToken = $tokens[$stackPtr]['parenthesis_opener'] ?? $stackPtr;
+
+        // These are the tokens that we are interested on.
+        $findTokens = array_merge($oneSpaceTokens, $noSpaceTokens);
+
+        // Find the first token that we are interested in.
+        $foundToken = $file->findPrevious($findTokens, $lastToken);
+
+        // Search backwards and examine all the matches found until we change of line.
+        while ($tokens[$foundToken]['line'] === $tokens[$lastToken]['line']) {
+            // If it's a token that requires one space after it, check if there is one.
+            if (in_array($tokens[$foundToken]['code'], $oneSpaceTokens) === true) {
+                $replacement = ' ';
+                if (
+                    $tokens[$foundToken + 1]['code'] === T_WHITESPACE && // We only check whitespace.
+                    $tokens[$foundToken + 1]['content'] !== ' '
+                ) {
+                    $error = 'Expected 1 space after "%s"; %s found';
+                    $data = [
+                        $tokens[$foundToken]['content'],
+                        strlen($tokens[$foundToken + 1]['content']),
+                    ];
+                    $fix = $file->addFixableError($error, $foundToken, 'OneExpectedAfter', $data);
+                    if ($fix === true) {
+                        $file->fixer->replaceToken($foundToken + 1, $replacement);
+                    }
+                }
+            }
+
+            // If it's a token that requires no space after it, check if there is none.
+            if (in_array($tokens[$foundToken]['code'], $noSpaceTokens) === true) {
+                $replacement = '';
+                $process = true;
+
+                // We only process T_STRING if it matches the method name.
+                if ($tokens[$foundToken]['code'] === T_STRING) {
+                    if ($tokens[$foundToken]['content'] !== $methodName) {
+                        $process = false;
+                    }
+                }
+
+                // We only process T_OPEN_PARENTHESIS if it has spaces, and only
+                // to get rid of them
+                if ($tokens[$foundToken]['code'] === T_OPEN_PARENTHESIS) {
+                    if (strpos($tokens[$foundToken + 1]['content'], ' ') !== false) {
+                        $replacement = str_replace(' ', '', $tokens[$foundToken + 1]['content']);
+                    } else {
+                        $process = false;
+                    }
+                }
+
+                if (
+                    $tokens[$foundToken + 1]['code'] === T_WHITESPACE && // We only check whitespace.
+                    $tokens[$foundToken + 1]['content'] !== '' &&
+                    $process === true
+                ) {
+                    $error = 'Expected 0 spaces after "%s"; %s found';
+                    $data = [
+                        $tokens[$foundToken]['content'],
+                        strlen($tokens[$foundToken + 1]['content']),
+                    ];
+                    $fix = $file->addFixableError($error, $foundToken, 'ZeroExpectedAfter', $data);
+                    if ($fix === true) {
+                        $file->fixer->replaceToken($foundToken + 1, $replacement);
+                    }
+                }
+            }
+
+            // Move to the previous interesting token.
+            $foundToken = $file->findPrevious($findTokens, $foundToken - 1);
+        }
+    }
+
+    protected function processTokenOutsideScope(File $file, $stackPtr) {
+        return;
+    }
+}

moodle/ruleset.xml

@@ -112,6 +112,10 @@
     -->
     <rule ref="PSR12.Files.ImportStatement.LeadingSlash"/>
 
+    <!-- PSR12 function return types (whitespace handling) -->
+    <rule ref="PSR12.Functions.ReturnTypeDeclaration"/>
+    <rule ref="PSR12.Functions.NullableTypeDeclaration"/>
+
     <!-- Let's add the complete PHPCompatibility standard -->
     <rule ref="PHPCompatibility" />