Adjust UnusedPrivateConstantRule for dynamic class constants

Author: ondrejmirtes

src/Rules/DeadCode/UnusedPrivateConstantRule.php

@@ -57,9 +57,6 @@ public function processNode(Node $node, Scope $scope): array
 
 		foreach ($node->getFetches() as $fetch) {
 			$fetchNode = $fetch->getNode();
-			if (!$fetchNode->name instanceof Node\Identifier) {
-				continue;
-			}
 
 			$fetchScope = $fetch->getScope();
 			if ($fetchNode->class instanceof Node\Name) {
@@ -68,6 +65,14 @@ public function processNode(Node $node, Scope $scope): array
 				$fetchedOnClass = $fetchScope->getType($fetchNode->class);
 			}
 
+			if (!$fetchNode->name instanceof Node\Identifier) {
+				if (!$classType->isSuperTypeOf($fetchedOnClass)->no()) {
+					$constants = [];
+					break;
+				}
+				continue;
+			}
+
 			$constantReflection = $fetchScope->getConstantReflection($fetchedOnClass, $fetchNode->name->toString());
 			if ($constantReflection === null) {
 				if (!$classType->isSuperTypeOf($fetchedOnClass)->no()) {

tests/PHPStan/Rules/DeadCode/UnusedPrivateConstantRuleTest.php

@@ -97,4 +97,19 @@ public function testBug9765(): void
 		$this->analyse([__DIR__ . '/data/bug-9765.php'], []);
 	}
 
+	public function testDynamicConstantFetch(): void
+	{
+		if (PHP_VERSION_ID < 80300) {
+			$this->markTestSkipped('Test requires PHP 8.3.');
+		}
+
+		$this->analyse([__DIR__ . '/data/unused-private-constant-dynamic-fetch.php'], [
+			[
+				'Constant UnusedPrivateConstantDynamicFetch\Baz::FOO is unused.',
+				32,
+				'See: https://phpstan.org/developing-extensions/always-used-class-constants',
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/DeadCode/data/unused-private-constant-dynamic-fetch.php

@@ -0,0 +1,39 @@
+<?php // lint >= 8.3
+
+namespace UnusedPrivateConstantDynamicFetch;
+
+class Foo
+{
+
+	private const FOO = 1;
+
+	public function doFoo(string $s): void
+	{
+		echo self::{$s};
+	}
+
+}
+
+class Bar
+{
+
+	private const FOO = 1;
+
+	public function doFoo(self $a, string $s): void
+	{
+		echo $a::{$s};
+	}
+
+}
+
+class Baz
+{
+
+	private const FOO = 1;
+
+	public function doFoo(\stdClass $a, string $s): void
+	{
+		echo $a::{$s};
+	}
+
+}