Introduce ProcessPromise interface for the PHPStan Pro worker

ProcessPromise becomes an interface describing the fixer:worker process
as seen by FixerApplication; the existing react/child-process
implementation is renamed to SpawnedProcessPromise. FixerApplication
creates it through a factory method. Sole implementation for now — a
pcntl_fork() based one follows.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ondrejmirtes

src/Command/FixerApplication.php

@@ -28,6 +28,7 @@
 use PHPStan\Process\ProcessCrashedException;
 use PHPStan\Process\ProcessHelper;
 use PHPStan\Process\ProcessPromise;
+use PHPStan\Process\SpawnedProcessPromise;
 use PHPStan\ShouldNotHappenException;
 use React\ChildProcess\Process;
 use React\EventLoop\LoopInterface;
@@ -446,16 +447,7 @@ private function analyse(
 			});
 		});
 
-		$process = new ProcessPromise($loop, ProcessHelper::getWorkerCommand(
-			$mainScript,
-			'fixer:worker',
-			$projectConfigFile,
-			[
-				'--server-port',
-				(string) $serverPort,
-			],
-			$input,
-		));
+		$process = $this->createProcessPromise($loop, $mainScript, $projectConfigFile, $input, $serverPort);
 		$this->processInProgress = $process->run();
 
 		$this->processInProgress->then(function () use ($server): void {
@@ -566,4 +558,27 @@ private function getStubFiles(): array
 		return $stubFiles;
 	}
 
+	/**
+	 * @param int<0, 65535> $serverPort
+	 */
+	private function createProcessPromise(
+		LoopInterface $loop,
+		string $mainScript,
+		?string $projectConfigFile,
+		InputInterface $input,
+		int $serverPort,
+	): ProcessPromise
+	{
+		return new SpawnedProcessPromise($loop, ProcessHelper::getWorkerCommand(
+			$mainScript,
+			'fixer:worker',
+			$projectConfigFile,
+			[
+				'--server-port',
+				(string) $serverPort,
+			],
+			$input,
+		));
+	}
+
 }

src/Process/ProcessPromise.php

@@ -2,91 +2,23 @@
 
 namespace PHPStan\Process;
 
-use PHPStan\ShouldNotHappenException;
-use React\ChildProcess\Process;
-use React\EventLoop\LoopInterface;
-use React\Promise\Deferred;
 use React\Promise\PromiseInterface;
-use function fclose;
-use function rewind;
-use function stream_get_contents;
-use function tmpfile;
 
-final class ProcessPromise
+/**
+ * A PHPStan Pro analysis worker as seen by FixerApplication.
+ *
+ * Implementations differ only in how the worker process comes to life:
+ * SpawnedProcessPromise spawns a fresh PHP process via react/child-process,
+ * ForkedProcessPromise forks the already-booted main process via pcntl_fork().
+ * Both yield a promise that resolves on success and rejects with
+ * ProcessCrashedException / ProcessCanceledException otherwise.
+ */
+interface ProcessPromise
 {
 
-	/** @var Deferred<string> */
-	private Deferred $deferred;
-
-	private ?Process $process = null;
-
-	private bool $canceled = false;
-
-	public function __construct(private LoopInterface $loop, private string $command)
-	{
-		$this->deferred = new Deferred(function (): void {
-			$this->cancel();
-		});
-	}
-
 	/**
 	 * @return PromiseInterface<string>
 	 */
-	public function run(): PromiseInterface
-	{
-		$tmpStdOutResource = tmpfile();
-		if ($tmpStdOutResource === false) {
-			throw new ShouldNotHappenException('Failed creating temp file for stdout.');
-		}
-		$tmpStdErrResource = tmpfile();
-		if ($tmpStdErrResource === false) {
-			throw new ShouldNotHappenException('Failed creating temp file for stderr.');
-		}
-
-		$this->process = new Process($this->command, fds: [
-			1 => $tmpStdOutResource,
-			2 => $tmpStdErrResource,
-		]);
-		$this->process->start($this->loop);
-
-		$this->process->on('exit', function ($exitCode) use ($tmpStdOutResource, $tmpStdErrResource): void {
-			if ($this->canceled) {
-				fclose($tmpStdOutResource);
-				fclose($tmpStdErrResource);
-				return;
-			}
-			rewind($tmpStdOutResource);
-			$stdOut = stream_get_contents($tmpStdOutResource);
-			fclose($tmpStdOutResource);
-
-			rewind($tmpStdErrResource);
-			$stdErr = stream_get_contents($tmpStdErrResource);
-			fclose($tmpStdErrResource);
-
-			if ($exitCode === null) {
-				$this->deferred->reject(new ProcessCrashedException($stdOut . $stdErr));
-				return;
-			}
-
-			if ($exitCode === 0) {
-				$this->deferred->resolve($stdOut);
-				return;
-			}
-
-			$this->deferred->reject(new ProcessCrashedException($stdOut . $stdErr));
-		});
-
-		return $this->deferred->promise();
-	}
-
-	private function cancel(): void
-	{
-		if ($this->process === null) {
-			throw new ShouldNotHappenException('Cancelling process before running');
-		}
-		$this->canceled = true;
-		$this->process->terminate();
-		$this->deferred->reject(new ProcessCanceledException());
-	}
+	public function run(): PromiseInterface;
 
 }

src/Process/SpawnedProcessPromise.php

@@ -0,0 +1,98 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Process;
+
+use PHPStan\ShouldNotHappenException;
+use React\ChildProcess\Process;
+use React\EventLoop\LoopInterface;
+use React\Promise\Deferred;
+use React\Promise\PromiseInterface;
+use function fclose;
+use function rewind;
+use function stream_get_contents;
+use function tmpfile;
+
+/**
+ * ProcessPromise backed by a freshly spawned PHP process (react/child-process).
+ *
+ * @see ForkedProcessPromise for the pcntl_fork()-based alternative that skips
+ * the per-worker application re-boot.
+ */
+final class SpawnedProcessPromise implements ProcessPromise
+{
+
+	/** @var Deferred<string> */
+	private Deferred $deferred;
+
+	private ?Process $process = null;
+
+	private bool $canceled = false;
+
+	public function __construct(private LoopInterface $loop, private string $command)
+	{
+		$this->deferred = new Deferred(function (): void {
+			$this->cancel();
+		});
+	}
+
+	/**
+	 * @return PromiseInterface<string>
+	 */
+	public function run(): PromiseInterface
+	{
+		$tmpStdOutResource = tmpfile();
+		if ($tmpStdOutResource === false) {
+			throw new ShouldNotHappenException('Failed creating temp file for stdout.');
+		}
+		$tmpStdErrResource = tmpfile();
+		if ($tmpStdErrResource === false) {
+			throw new ShouldNotHappenException('Failed creating temp file for stderr.');
+		}
+
+		$this->process = new Process($this->command, fds: [
+			1 => $tmpStdOutResource,
+			2 => $tmpStdErrResource,
+		]);
+		$this->process->start($this->loop);
+
+		$this->process->on('exit', function ($exitCode) use ($tmpStdOutResource, $tmpStdErrResource): void {
+			if ($this->canceled) {
+				fclose($tmpStdOutResource);
+				fclose($tmpStdErrResource);
+				return;
+			}
+			rewind($tmpStdOutResource);
+			$stdOut = stream_get_contents($tmpStdOutResource);
+			fclose($tmpStdOutResource);
+
+			rewind($tmpStdErrResource);
+			$stdErr = stream_get_contents($tmpStdErrResource);
+			fclose($tmpStdErrResource);
+
+			if ($exitCode === null) {
+				$this->deferred->reject(new ProcessCrashedException($stdOut . $stdErr));
+				return;
+			}
+
+			if ($exitCode === 0) {
+				$this->deferred->resolve($stdOut);
+				return;
+			}
+
+			$this->deferred->reject(new ProcessCrashedException($stdOut . $stdErr));
+		});
+
+		return $this->deferred->promise();
+	}
+
+	private function cancel(): void
+	{
+		if ($this->process === null) {
+			throw new ShouldNotHappenException('Cancelling process before running');
+		}
+		$this->canceled = true;
+		$this->process->terminate();
+		$this->deferred->reject(new ProcessCanceledException());
+	}
+
+}