Add test for compact used within arrow function

Author: sirbrillig

Tests/VariableAnalysisSniff/VariableAnalysisTest.php

@@ -522,6 +522,8 @@ public function testCompactWarnings()
 			23,
 			26,
 			36,
+			41,
+			42,
 		];
 		$this->assertSame($expectedWarnings, $lines);
 	}
@@ -543,6 +545,8 @@ public function testCompactWarningsHaveCorrectSniffCodes()
 		$this->assertSame(self::UNDEFINED_ERROR_CODE, $warnings[26][66][0]['source']);
 		$this->assertSame(self::UNUSED_ERROR_CODE, $warnings[36][5][0]['source']);
 		$this->assertSame(self::UNDEFINED_ERROR_CODE, $warnings[36][23][0]['source']);
+		$this->assertSame(self::UNUSED_ERROR_CODE, $warnings[41][22][0]['source']);
+		$this->assertSame(self::UNDEFINED_ERROR_CODE, $warnings[42][39][0]['source']);
 	}
 
 	public function testTraitAllowsThis()

Tests/VariableAnalysisSniff/fixtures/CompactFixture.php

@@ -35,3 +35,14 @@ function foo() {
     $a = 'Hello';
     $c = compact( $a, $b ); // Unused variable c and undefined variable b
 }
+
+function function_with_arrow_function_and_compact() {
+	$make_array = fn ($arg) => compact('arg');
+	$make_nothing = fn ($arg) => []; // Unused variable $arg
+	$make_no_variable = fn () => compact('arg') // Undefined variable $arg
+	echo $make_array('hello');
+	echo $make_nothing('hello');
+	echo $make_no_variable();
+	$make_array_multiple = fn ($arg1, $arg2, $arg3) => compact('arg1', 'arg2', 'arg3');
+	echo $make_array_multiple();
+}