Report error when trying to instantiate a trait with new

- Added trait check to InstantiationRule alongside existing checks for enums, interfaces, and abstract classes
- New error message: "Cannot instantiate trait X." with identifier "new.trait"
- New regression test in tests/PHPStan/Rules/Classes/data/bug-14251.php

Closes phpstan/phpstan#14251

Author: phpstan-bot

src/Rules/Classes/InstantiationRule.php

@@ -156,6 +156,14 @@ private function checkClassName(string $class, bool $isName, Node $node, Scope $
 			$classReflection = $this->reflectionProvider->getClass($class);
 		}
 
+		if ($classReflection->isTrait() && $isName) {
+			return [
+				RuleErrorBuilder::message(
+					sprintf('Cannot instantiate trait %s.', $classReflection->getDisplayName()),
+				)->identifier('new.trait')->build(),
+			];
+		}
+
 		if ($classReflection->isEnum() && $isName) {
 			return [
 				RuleErrorBuilder::message(

tests/PHPStan/Rules/Classes/InstantiationRuleTest.php

@@ -599,4 +599,14 @@ public function testNewStaticWithConsistentConstructor(): void
 		]);
 	}
 
+	public function testBug14251(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-14251.php'], [
+			[
+				'Cannot instantiate trait Bug14251\InternalTrait.',
+				9,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Classes/data/bug-14251.php

@@ -0,0 +1,9 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14251;
+
+trait InternalTrait {
+	public function doSomething(): void {}
+}
+
+$obj = new InternalTrait();