Memoize file contents by path in CachedParser to skip redundant reads

src/Parser/CachedParser.php

@@ -5,6 +5,8 @@
 use PhpParser\Node;
 use PHPStan\File\FileReader;
 use function array_slice;
+use function clearstatcache;
+use function filemtime;
 
 final class CachedParser implements Parser
 {
@@ -17,6 +19,9 @@ final class CachedParser implements Parser
 	/** @var array<string, true> */
 	private array $parsedByString = [];
 
+	/** @var array<string, array{int, string}> path => [mtime, source code] */
+	private array $cachedSourceByFile = [];
+
 	public function __construct(
 		private Parser $originalParser,
 		private int $cachedNodesByStringCountMax,
@@ -40,7 +45,20 @@ public function parseFile(string $file): array
 			--$this->cachedNodesByStringCount;
 		}
 
-		$sourceCode = FileReader::read($file);
+		// parseFile is called once per class using a trait, so the same file is read many times.
+		// Memoize the contents by path, keyed by mtime; clearstatcache keeps this correct when a file
+		// changes between calls in a long-running process (PHPStan Pro, fixer worker).
+		clearstatcache(true, $file);
+		$mtime = @filemtime($file);
+		if ($mtime !== false && isset($this->cachedSourceByFile[$file]) && $this->cachedSourceByFile[$file][0] === $mtime) {
+			$sourceCode = $this->cachedSourceByFile[$file][1];
+		} else {
+			$sourceCode = FileReader::read($file);
+			if ($mtime !== false) {
+				$this->cachedSourceByFile[$file] = [$mtime, $sourceCode];
+			}
+		}
+
 		if (!isset($this->cachedNodesByString[$sourceCode]) || isset($this->parsedByString[$sourceCode])) {
 			$this->cachedNodesByString[$sourceCode] = $this->originalParser->parseFile($file);
 			$this->cachedNodesByStringCount++;

tests/PHPStan/Parser/CachedParserTest.php

@@ -5,12 +5,19 @@
 use Generator;
 use PhpParser\Node;
 use PhpParser\Node\Stmt\Namespace_;
+use PhpParser\Node\Stmt\Nop;
 use PHPStan\BetterReflection\Reflection\ExprCacheHelper;
 use PHPStan\File\FileHelper;
 use PHPStan\File\FileReader;
 use PHPStan\Testing\PHPStanTestCase;
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\MockObject\Stub;
+use function file_put_contents;
+use function sys_get_temp_dir;
+use function time;
+use function touch;
+use function uniqid;
+use function unlink;
 
 class CachedParserTest extends PHPStanTestCase
 {
@@ -171,4 +178,38 @@ public function testWithExprCacheHelper(): void
 		$this->assertSame(['startLine' => 1, 'startTokenPos' => 35, 'startFilePos' => 137, 'endLine' => 10, 'endTokenPos' => 35, 'endFilePos' => 143, 'kind' => 1, 'rawValue' => "'hello'"], $reImported->getAttributes());
 	}
 
+	public function testParseFileSkipsReadingUnchangedFileAndRereadsAfterChange(): void
+	{
+		$parser = new CachedParser($this->getContentEchoingParserStub(), 500);
+		$path = sys_get_temp_dir() . '/phpstan-cached-parser-' . uniqid() . '.php';
+		$baseTime = time() - 10;
+
+		try {
+			file_put_contents($path, 'first contents');
+			touch($path, $baseTime);
+			$this->assertSame('first contents', $parser->parseFile($path)[0]->getAttribute('content'));
+
+			// Contents change but the mtime does not: the memoized contents are returned without re-reading.
+			file_put_contents($path, 'second contents');
+			touch($path, $baseTime);
+			$this->assertSame('first contents', $parser->parseFile($path)[0]->getAttribute('content'));
+
+			// A newer mtime invalidates the memo, so the file is read again.
+			touch($path, $baseTime + 10);
+			$this->assertSame('second contents', $parser->parseFile($path)[0]->getAttribute('content'));
+		} finally {
+			@unlink($path);
+		}
+	}
+
+	private function getContentEchoingParserStub(): Parser&Stub
+	{
+		$mock = $this->createStub(Parser::class);
+		$mock->method('parseFile')->willReturnCallback(
+			static fn (string $file): array => [new Nop(['content' => FileReader::read($file)])],
+		);
+
+		return $mock;
+	}
+
 }