Add regression test for static caching of FunctionSignatureMapProvider

- New test in tests/PHPStan/Reflection/SignatureMap/FunctionSignatureMapProviderTest.php
- Verifies that creating a second FunctionSignatureMapProvider instance reuses the
  static cache instead of reloading the ~7MB functionMap.php file
- The fix (commit 394064b) changed signatureMaps and functionMetadata from instance
  properties to static properties, preventing repeated loading in test suites

Closes phpstan/phpstan#10039

Author: staabm

tests/PHPStan/Reflection/SignatureMap/FunctionSignatureMapProviderTest.php

@@ -0,0 +1,48 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Reflection\SignatureMap;
+
+use PHPStan\Php\PhpVersion;
+use PHPStan\Reflection\InitializerExprTypeResolver;
+use PHPStan\Testing\PHPStanTestCase;
+use function memory_get_usage;
+
+class FunctionSignatureMapProviderTest extends PHPStanTestCase
+{
+
+	/**
+	 * Regression test for https://github.com/phpstan/phpstan/issues/10039
+	 *
+	 * The signature map and function metadata should be cached in static properties
+	 * so the large functionMap.php file is loaded once and shared across all instances.
+	 * Without static caching, each new DI container (e.g., in test suites) would reload
+	 * the entire ~7MB functionMap.php, causing excessive memory usage.
+	 */
+	public function testBug10039(): void
+	{
+		$parser = self::getContainer()->getByType(SignatureMapParser::class);
+		$initializerResolver = self::getContainer()->getByType(InitializerExprTypeResolver::class);
+		$phpVersion = new PhpVersion(80200);
+
+		// Create first instance and load the signature map
+		$provider1 = new FunctionSignatureMapProvider($parser, $initializerResolver, $phpVersion, false);
+		$provider1->getSignatureMap();
+
+		// Create a second instance with the same parameters
+		$provider2 = new FunctionSignatureMapProvider($parser, $initializerResolver, $phpVersion, false);
+
+		// With static caching, the second call should not allocate significant memory
+		// because it returns the already-cached map. Without static caching (the bug),
+		// each instance would load and process the entire functionMap.php (~7MB).
+		$memBefore = memory_get_usage();
+		$provider2->getSignatureMap();
+		$memDiff = memory_get_usage() - $memBefore;
+
+		$this->assertLessThan(
+			1024 * 1024, // 1 MB - the full load uses ~7 MB
+			$memDiff,
+			'Second FunctionSignatureMapProvider instance should reuse the static cache, not reload functionMap.php',
+		);
+	}
+
+}