prevent Psalm from considering throwing methods as unused just because they're immutable

src/Psalm/Internal/Analyzer/Statements/Expression/Call/Method/MethodCallPurityAnalyzer.php

@@ -112,6 +112,7 @@ public static function analyze(
                     && !$method_storage->assertions
                     && !$method_storage->if_true_assertions
                     && !$method_storage->if_false_assertions
+                    && !$method_storage->throws
                 ) {
                     if (IssueBuffer::accepts(
                         new \Psalm\Issue\UnusedMethodCall(

tests/UnusedCodeTest.php

@@ -1162,6 +1162,27 @@ private function assert(?string $val): void {
                     $a = new A();
                     echo $a->getVal(null);',
             ],
+            'NotUnusedWhenThrows' => [
+                '<?php
+                    declare(strict_types=1);
+
+                    /** @psalm-immutable */
+                    final class UserList
+                    {
+                        /**
+                         * @throws InvalidArgumentException
+                         */
+                        public function validate(): void
+                        {
+                            // Some validation happens here
+                            throw new \InvalidArgumentException();
+                        }
+                    }
+
+                    $a = new UserList();
+                    $a->validate();
+                    ',
+            ],
             '__halt_compiler_no_usage_check' => [
                 '<?php
                     exit(0);