Generic/UnusedFunctionParameter: ignore class context for closures/arrow functions

As things were, if a closure or arrow function declared within a class which extends or implements would have an unused function parameter, it would get the `InExtendedClass` or `InImplementedInterface` addition in the error code.

Those additions were only intended for function declarations where the declaration would potentially be overloading a method from a parent and would have to comply with the method signature of the method in the parent class/interface.

This could lead to underreporting if a standard explicitly excludes the error codes contain `InExtendedClass` and/or `InImplementedInterface`.

Fixed now.

Includes additional unit test, though the tests don't safeguard this much as they don't check the error codes of the messages thrown.

The change can be tested manually by running the new tests against `master`, which will show:
```
 163 | WARNING | The method parameter $d is never used (Generic.CodeAnalysis.UnusedFunctionParameter.FoundInExtendedClassAfterLastUsed)
 172 | WARNING | The method parameter $d is never used
     |         | (Generic.CodeAnalysis.UnusedFunctionParameter.FoundInImplementedInterfaceAfterLastUsed)
```

... while with the change in this commit, this will be fixed to:
```
 163 | WARNING | The method parameter $d is never used (Generic.CodeAnalysis.UnusedFunctionParameter.FoundAfterLastUsed)
 172 | WARNING | The method parameter $d is never used (Generic.CodeAnalysis.UnusedFunctionParameter.FoundAfterLastUsed)
```

Author: jrfnl

CHANGELOG.md

@@ -114,6 +114,8 @@ The file documents changes to the PHP_CodeSniffer project.
     - Thanks to Juliette Reinders Folmer (@jrfnl) for the patch
 - Fixed bug #3557 : Squiz.Arrays.ArrayDeclaration will now ignore PHP 7.4 array unpacking when determining whether an array is associative
     - Thanks to Volker Dusch (@edorian) for the patch
+- Fixed bug #3715 : Generic/UnusedFunctionParameter: fixed incorrect errorcode for closures/arrow functions nested within extended classes/classes which implement.
+    - Thanks to Juliette Reinders Folmer (@jrfnl) for the patch
 - Fixed bug #3717 : Squiz.Commenting.FunctionComment: fixed false positive for InvalidNoReturn when type is never
     - Thanks to Choraimy Kroonstuiver (@axlon) for the patch
 - Fixed bug #3720 : Generic/RequireStrictTypes : will now bow out silently in case of parse errors/live coding instead of throwing false positives/false negatives

src/Standards/Generic/Sniffs/CodeAnalysis/UnusedFunctionParameterSniff.php

@@ -69,14 +69,17 @@ public function process(File $phpcsFile, $stackPtr)
         $errorCode  = 'Found';
         $implements = false;
         $extends    = false;
-        $classPtr   = $phpcsFile->getCondition($stackPtr, T_CLASS);
-        if ($classPtr !== false) {
-            $implements = $phpcsFile->findImplementedInterfaceNames($classPtr);
-            $extends    = $phpcsFile->findExtendedClassName($classPtr);
-            if ($extends !== false) {
-                $errorCode .= 'InExtendedClass';
-            } else if ($implements !== false) {
-                $errorCode .= 'InImplementedInterface';
+
+        if ($token['code'] === T_FUNCTION) {
+            $classPtr   = $phpcsFile->getCondition($stackPtr, T_CLASS);
+            if ($classPtr !== false) {
+                $implements = $phpcsFile->findImplementedInterfaceNames($classPtr);
+                $extends    = $phpcsFile->findExtendedClassName($classPtr);
+                if ($extends !== false) {
+                    $errorCode .= 'InExtendedClass';
+                } else if ($implements !== false) {
+                    $errorCode .= 'InImplementedInterface';
+                }
             }
         }
 

src/Standards/Generic/Tests/CodeAnalysis/UnusedFunctionParameterUnitTest.inc

@@ -152,3 +152,23 @@ class ConstructorPropertyPromotionWithContentInMethod {
 }
 
 $found = in_array_cb($needle, $haystack, fn($array, $needle) => $array[2] === $needle);
+
+
+/*
+ * Don't adjust the error code for closures and arrow functions in extended classes/classes implementing interfaces.
+ */
+class MyExtendedClass extends SomeClass {
+    public function something($a, $b) {
+        $c = $a + $b;
+        $closure = function ($c, $d) {
+            return $c * 2;
+        };
+    }
+}
+
+class MyExtendedClass implements SomeInterface {
+    public function something($a, $b) {
+        $c = $a + $b;
+        $fn = fn($c, $d) => $c[2];
+    }
+}

src/Standards/Generic/Tests/CodeAnalysis/UnusedFunctionParameterUnitTest.php

@@ -50,6 +50,8 @@ public function getWarningList()
             117 => 1,
             121 => 2,
             125 => 2,
+            163 => 1,
+            172 => 1,
         ];
 
     }//end getWarningList()