Do not call a cache file that vanished mid-read corrupted

src/Analyser/ResultCache/ResultCacheManager.php

@@ -43,6 +43,7 @@
 use function array_unique;
 use function array_values;
 use function class_exists;
+use function clearstatcache;
 use function count;
 use function error_get_last;
 use function explode;
@@ -336,10 +337,22 @@ public function restore(array $allAnalysedFiles, bool $debug, bool $onlyFiles, ?
 		}
 
 		if (!is_array($data)) {
+			// readCacheFile() returns null both for a file it could not read back and for one it could
+			// not open at all, and the second is not a corruption: the file was there for the is_file()
+			// check above and gone by the time it was opened. A concurrent clear-result-cache, a temp
+			// directory being swept, a CI cache artifact expiring mid-run. Calling that corrupt sends
+			// someone looking for a broken disk. Ask before the unlink below, which removes the file
+			// in both cases, and clear the stat cache first: PHP may still answer from the is_file()
+			// check above.
+			clearstatcache(true, $cacheFilePath);
+			$reason = is_file($cacheFilePath)
+				? 'Result cache not used because the cache file is corrupted.'
+				: 'Result cache not used because the cache file disappeared while it was being read.';
+
 			@unlink($cacheFilePath);
 
 			return $this->fullAnalysis(
-				'Result cache not used because the cache file is corrupted.',
+				$reason,
 				$allAnalysedFiles,
 				$this->getMeta($allAnalysedFiles, $projectConfigArray),
 				$currentFileHashes,

tests/PHPStan/Analyser/ResultCache/ResultCacheManagerCorruptedFileTest.php

@@ -0,0 +1,56 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Analyser\ResultCache;
+
+use Override;
+use PHPStan\Command\Output;
+use PHPStan\File\FileWriter;
+use PHPStan\Testing\PHPStanTestCase;
+use function dirname;
+use function is_dir;
+use function is_file;
+use function mkdir;
+use function unlink;
+
+class ResultCacheManagerCorruptedFileTest extends PHPStanTestCase
+{
+
+	/**
+	 * A real file on purpose: deleting it clears PHP's stat cache, so a check that runs after the
+	 * unlink sees the file as gone. A stream wrapper cannot reproduce that.
+	 */
+	public function testCorruptedCacheFileIsReportedAsCorrupted(): void
+	{
+		$cacheFilePath = self::getContainer()->getParameter('resultCachePath');
+		if (!is_dir(dirname($cacheFilePath))) {
+			mkdir(dirname($cacheFilePath), 0777, true);
+		}
+		FileWriter::write($cacheFilePath, "garbage\n");
+
+		$manager = self::getContainer()->getByType(ResultCacheManagerFactory::class)->create([]);
+		$resultCache = $manager->restore([], false, false, null, $this->createStub(Output::class));
+
+		$this->assertTrue($resultCache->isFullAnalysis());
+		$this->assertSame('Result cache not used because the cache file is corrupted.', $resultCache->getFullAnalysisReason());
+		$this->assertFalse(is_file($cacheFilePath));
+	}
+
+	#[Override]
+	protected function tearDown(): void
+	{
+		$cacheFilePath = self::getContainer()->getParameter('resultCachePath');
+		if (is_file($cacheFilePath)) {
+			unlink($cacheFilePath);
+		}
+
+		parent::tearDown();
+	}
+
+	public static function getAdditionalConfigFiles(): array
+	{
+		return [
+			__DIR__ . '/data/result-cache-corrupted.neon',
+		];
+	}
+
+}

tests/PHPStan/Analyser/ResultCache/ResultCacheManagerVanishedFileTest.php

@@ -0,0 +1,46 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Analyser\ResultCache;
+
+use Override;
+use PHPStan\Command\Output;
+use PHPStan\Testing\PHPStanTestCase;
+use function stream_wrapper_register;
+use function stream_wrapper_unregister;
+
+class ResultCacheManagerVanishedFileTest extends PHPStanTestCase
+{
+
+	protected function setUp(): void
+	{
+		parent::setUp();
+
+		ResultCacheStreamWrapper::$deleted = false;
+		stream_wrapper_register(ResultCacheStreamWrapper::SCHEME, ResultCacheStreamWrapper::class);
+	}
+
+	#[Override]
+	protected function tearDown(): void
+	{
+		stream_wrapper_unregister(ResultCacheStreamWrapper::SCHEME);
+
+		parent::tearDown();
+	}
+
+	public function testCacheFileThatVanishedBeforeOpeningIsNotReportedAsCorrupted(): void
+	{
+		$manager = self::getContainer()->getByType(ResultCacheManagerFactory::class)->create([]);
+		$resultCache = $manager->restore([], false, false, null, $this->createStub(Output::class));
+
+		$this->assertTrue($resultCache->isFullAnalysis());
+		$this->assertSame('Result cache not used because the cache file disappeared while it was being read.', $resultCache->getFullAnalysisReason());
+	}
+
+	public static function getAdditionalConfigFiles(): array
+	{
+		return [
+			__DIR__ . '/data/result-cache-vanished.neon',
+		];
+	}
+
+}

tests/PHPStan/Analyser/ResultCache/ResultCacheStreamWrapper.php

@@ -0,0 +1,48 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Analyser\ResultCache;
+
+use AllowDynamicProperties;
+
+/**
+ * A result cache file that passes the is_file() check and then refuses to open, the way a file does
+ * when something deletes it between the two. A real file cannot be made to do that without a race.
+ *
+ * PHP assigns the stream context to $context on every instance it creates, which is a dynamic
+ * property nothing here reads.
+ *
+ * phpcs:disable PSR1.Methods.CamelCapsMethodName.NotCamelCaps
+ */
+#[AllowDynamicProperties]
+final class ResultCacheStreamWrapper
+{
+
+	public const SCHEME = 'phpstan-result-cache-test';
+
+	public static bool $deleted = false;
+
+	/**
+	 * @return array<string, int>|false
+	 */
+	public function url_stat(string $path, int $flags)
+	{
+		if (self::$deleted) {
+			return false;
+		}
+
+		return ['mode' => 0100644, 'size' => 8];
+	}
+
+	public function stream_open(string $path, string $mode, int $options, ?string &$openedPath): bool
+	{
+		self::$deleted = true;
+
+		return false;
+	}
+
+	public function unlink(string $path): bool
+	{
+		return true;
+	}
+
+}

tests/PHPStan/Analyser/ResultCache/data/result-cache-corrupted.neon

@@ -0,0 +1,2 @@
+parameters:
+	resultCachePath: %tmpDir%/result-cache-manager-restore-test/resultCache.php

tests/PHPStan/Analyser/ResultCache/data/result-cache-vanished.neon

@@ -0,0 +1,2 @@
+parameters:
+	resultCachePath: phpstan-result-cache-test://resultCache.php