feat: add PHPCS sniff to disallow alternative (colon) control-structu…

.phpcs/StarterKitStandard/Sniffs/ControlStructures/DisallowAlternativeSyntaxSniff.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace StarterKitStandard\Sniffs\ControlStructures;
+
+use PHP_CodeSniffer\Files\File;
+use PHP_CodeSniffer\Sniffs\Sniff;
+
+/**
+ * Disallows alternative (colon) control-structure syntax.
+ *
+ * PHP only emits T_ENDIF/T_ENDFOREACH/T_ENDWHILE/T_ENDFOR/T_ENDSWITCH tokens when the
+ * alternative `if (...) : ... endif;` syntax is used, so matching directly on those end
+ * tokens is sufficient - no need to inspect scope openers/closers.
+ */
+final class DisallowAlternativeSyntaxSniff implements Sniff
+{
+    /**
+     * @return array<int, int>
+     */
+    public function register()
+    {
+        return [
+            T_ENDIF,
+            T_ENDFOREACH,
+            T_ENDWHILE,
+            T_ENDFOR,
+            T_ENDSWITCH,
+        ];
+    }
+
+    /**
+     * @param File $phpcsFile
+     * @param int  $stackPtr
+     *
+     * @return void
+     */
+    public function process(File $phpcsFile, $stackPtr)
+    {
+        $tokens = $phpcsFile->getTokens();
+        $keyword = $tokens[$stackPtr]['content'];
+
+        $phpcsFile->addError(
+            'Alternative control-structure syntax ("%s") is not allowed; use brace syntax instead.',
+            $stackPtr,
+            'Found',
+            [$keyword]
+        );
+    }
+}

phpcs.xml

@@ -53,6 +53,8 @@
        namespace/ABSPATH guard, never loaded as-is. The rest of stubs/ is real PHP copied verbatim
        into the theme root during conversion, so it stays linted (must pass composer lint). -->
   <exclude-pattern>*/stubs/*.snippet.php</exclude-pattern>
+  <!-- Custom sniff tooling, not theme code - not scanned against theme style rules. -->
+  <exclude-pattern>*/.phpcs/*</exclude-pattern>
 
   <!--
   #############################################################################
@@ -72,4 +74,8 @@
   <!-- Use PHPCompatibilityWP standard -->
   <rule ref="PHPCompatibilityWP"/>
 
+  <!-- Disallow alternative (colon) control-structure syntax (if/endif, foreach/endforeach, ...)
+       - required by stubs/classic-theme/CONVERT.md's brace-syntax rule for classic templates. -->
+  <rule ref="./.phpcs/StarterKitStandard/Sniffs/ControlStructures/DisallowAlternativeSyntaxSniff.php"/>
+
 </ruleset>