PHP: Use auto_prepend_file to preload mu-plugins (instead of creating…

… them in wp-content/mu-plugins) (#1366)

This PR moves the Playground mu-plugins from
`/wordpress/wp-content/mu-plugins`, where they may interfere with the
user-provided files and pollute the git repository, to
`/internal/mu-plugins`, where they're invisible to the Playground
consumer and don't show up in exports or OPFS mounts.

Closes #1318

## Changes made

Technically, this PR uses the `auto_prepend_file` PHP options to
pre-load the following script:

```php
<?php
foreach (glob('/internal/preload/*.php') as $file) {
	require_once $file;
}
```

From here, preloading files is as simple as creating them in
`/internal/preload`. This PR ships a few such preloaded files:

* `consts.php`, that enables predefining PHP constants without affecting
`wp-config.php`.
* `env.php`, that preloads mu-plugins from `/internal/mu-plugins` using
[the method described
by](#1318 (comment))
@brandonpayton.
* `phpinfo.php`, that just calls `phpinfo();` when the request URL is
`/phpinfo.php` – this prevents creating an actual `phpinfo.php` file in
the document root. This involves a slight change in the path resolution
logic which will have to change even more soon to solve #1365.

From there, the SQLite integration plugin and the Playground mu-plugins
are placed in `/internal/mu-plugins` and do not affect the WordPress
file structure.

This PR also reduces code duplication by moving some parts of the
WordPress setup to the `@wp-playground/wordpress` package where they can
be imported by both the web and the CLI versions of Playground. We'll
only see more of these moving forward.

## Follow-up work

* Define clear use-cases and behaviors related to the location of
Playground-provided files. E.g. Full site export, where we want to keep
the SQLite integration plugin, or a GitHub repo, where we only want to
keep track of our changes in wp-content.
* Use `@wp-playground/cli` to build and setup WordPress in
`packages/playground/wordpress-builds/build/Dockerfile`
* Playground web: do not ship the SQLite integration plugin in the
pre-built `wp-content` directory. Source it from the
`/internal/mu-plugins` directory same way as in the CLI build.
* Do not create the drop-in plugin `wp-content/db.php`
* Do not install the WordPress importer plugin in `wp-content/plugins`
* Figure out how to avoid touching `wp-config.php` – defining PHP
constants may require rewriting it and it might be desirable to keep
those changes on export

## Testing instructions

* Confirm the tests pass
* In the browser – export Playground as zip, import it, also refresh the
page and import again, confirm it all worked.

packages/php-wasm/compile/php/phpwasm-emscripten-library.js

@@ -20,6 +20,9 @@ const LibraryExample = {
 			// stdout, stderr, and headers information are written for the JavaScript
 			// code to read later on.
 			FS.mkdir("/internal");
+			// The files from the preload directory are preloaded using the
+			// auto_prepend_file php.ini directive.
+			FS.mkdir("/internal/preload");
 
 			PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE
 				? require('events').EventEmitter

packages/php-wasm/node/public/php_7_0.js

@@ -5562,7 +5562,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/php-wasm/node/public/php_7_1.js

@@ -5562,7 +5562,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/php-wasm/node/public/php_7_2.js

@@ -5562,7 +5562,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/php-wasm/node/public/php_7_3.js

@@ -5562,7 +5562,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/php-wasm/node/public/php_7_4.js

@@ -5561,7 +5561,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/php-wasm/node/public/php_8_0.js

@@ -5561,7 +5561,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/php-wasm/node/public/php_8_1.js

@@ -5577,7 +5577,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/php-wasm/node/public/php_8_2.js

@@ -5582,7 +5582,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/php-wasm/node/public/php_8_3.js

@@ -5582,7 +5582,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/php-wasm/universal/src/lib/base-php.ts

@@ -358,32 +358,40 @@ export abstract class BasePHP implements IsomorphicLocalPHP, Disposable {
 	}
 
 	#initWebRuntime() {
+		this.writeFile(
+			'/internal/auto_prepend_file.php',
+			`<?php
+			foreach (glob('/internal/preload/*.php') as $file) {
+				require_once $file;
+			}
+		`
+		);
+		this.setPhpIniEntry(
+			'auto_prepend_file',
+			'/internal/auto_prepend_file.php'
+		);
 		/**
 		 * This creates a consts.php file in an in-memory
-		 * /internal directory and sets the auto_prepend_file PHP option
+		 * /internal/preload directory and sets the auto_prepend_file PHP option
 		 * to always load that file.
 		 * @see https://www.php.net/manual/en/ini.core.php#ini.auto-prepend-file
 		 *
 		 * Technically, this is a workaround. In the future, let's implement a
 		 * WASM SAPI method to pass consts directly.
 		 * @see https://github.com/WordPress/wordpress-playground/issues/750
 		 */
-		this.setPhpIniEntry('auto_prepend_file', '/internal/consts.php');
-		if (!this.fileExists('/internal/consts.php')) {
-			this.writeFile(
-				'/internal/consts.php',
-				`<?php
-				if(file_exists('/internal/consts.json')) {
-					$consts = json_decode(file_get_contents('/internal/consts.json'), true);
-					foreach ($consts as $const => $value) {
-						if (!defined($const) && is_scalar($value)) {
-							define($const, $value);
-						}
+		this.writeFile(
+			'/internal/preload/consts.php',
+			`<?php
+			if(file_exists('/internal/consts.json')) {
+				$consts = json_decode(file_get_contents('/internal/consts.json'), true);
+				foreach ($consts as $const => $value) {
+					if (!defined($const) && is_scalar($value)) {
+						define($const, $value);
 					}
-				}`
-			);
-		}
-
+				}
+			}`
+		);
 		if (this.#phpIniOverrides.length > 0) {
 			const overridesAsIni =
 				this.#phpIniOverrides

packages/php-wasm/universal/src/lib/index.ts

@@ -77,3 +77,4 @@ export {
 } from './urls';
 
 export { isExitCodeZero } from './is-exit-code-zero';
+export { proxyFileSystem } from './proxy-file-system';

packages/php-wasm/universal/src/lib/php-request-handler.ts

@@ -481,7 +481,12 @@ export class PHPRequestHandler<PHP extends BasePHP> {
 			filePath = '/index.php';
 		}
 
-		const resolvedFsPath = `${this.#DOCROOT}${filePath}`;
+		let resolvedFsPath = `${this.#DOCROOT}${filePath}`;
+		// If the requested PHP file doesn't exist, let's fall back to /index.php
+		// as the request may need to be rewritten.
+		if (!php.fileExists(resolvedFsPath)) {
+			resolvedFsPath = `${this.#DOCROOT}/index.php`;
+		}
 		if (php.fileExists(resolvedFsPath)) {
 			return resolvedFsPath;
 		}

packages/php-wasm/universal/src/lib/proxy-file-system.ts

@@ -0,0 +1,36 @@
+import { BasePHP } from './base-php';
+
+/**
+ * Proxy specific paths to the parent's MEMFS instance.
+ * This is useful for sharing the WordPress installation
+ * between the parent and child processes.
+ */
+export function proxyFileSystem(
+	sourceOfTruth: BasePHP,
+	replica: BasePHP,
+	paths: string[]
+) {
+	// We can't just import the symbol from the library because
+	// Playground CLI is built as ESM and php-wasm-node is built as
+	// CJS and the imported symbols will different in the production build.
+	const __private__symbol = Object.getOwnPropertySymbols(sourceOfTruth)[0];
+	for (const path of paths) {
+		if (!replica.fileExists(path)) {
+			replica.mkdir(path);
+		}
+		if (!sourceOfTruth.fileExists(path)) {
+			sourceOfTruth.mkdir(path);
+		}
+		// @ts-ignore
+		replica[__private__symbol].FS.mount(
+			// @ts-ignore
+			replica[__private__symbol].PROXYFS,
+			{
+				root: path,
+				// @ts-ignore
+				fs: sourceOfTruth[__private__symbol].FS,
+			},
+			path
+		);
+	}
+}

packages/php-wasm/web/public/kitchen-sink/php_8_3.js

@@ -5241,7 +5241,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/php-wasm/web/public/light/php_8_3.js

@@ -5241,7 +5241,7 @@ var allocateUTF8OnStack = stringToUTF8OnStack;
 
 var PHPWASM = {
  init: function() {
-  FS.mkdir("/internal");
+  FS.mkdir("/internal");FS.mkdir("/internal/preload");
   PHPWASM.EventEmitter = ENVIRONMENT_IS_NODE ? require("events").EventEmitter : class EventEmitter {
    constructor() {
     this.listeners = {};

packages/playground/cli/src/setup-php.ts

@@ -1,12 +1,13 @@
 import { NodePHP } from '@php-wasm/node';
 import {
-	BasePHP,
 	PHPRequestHandler,
 	SupportedPHPVersion,
+	proxyFileSystem,
 	rotatePHPRuntime,
 } from '@php-wasm/universal';
 import { rootCertificates } from 'tls';
 import { dirname } from '@php-wasm/util';
+import { envPHP_to_loadMuPlugins } from '@wp-playground/wordpress';
 
 export async function createPhp(
 	requestHandler: PHPRequestHandler<NodePHP>,
@@ -40,72 +41,43 @@ export async function createPhp(
 	php.setPhpIniEntry('openssl.cafile', '/tmp/ca-bundle.crt');
 	php.writeFile('/tmp/ca-bundle.crt', rootCertificates.join('\n'));
 
+	php.writeFile('/internal/preload/env.php', envPHP_to_loadMuPlugins);
+	php.writeFile(
+		'/internal/preload/phpinfo.php',
+		`<?php
+    // Render PHPInfo if the requested page is /phpinfo.php
+    if ( '/phpinfo.php' === $_SERVER['REQUEST_URI'] ) {
+        phpinfo();
+        exit;
+    }`
+	);
+	php.mkdir('/internal/mu-plugins');
+
 	if (!isPrimary) {
 		/**
 		 * @TODO: Consider an API similar to
 		 *
 		 * php.mount('/wordpress', primaryPHP.getMountPoint('/wordpress'));
 		 */
-		proxyFileSystem(
-			await requestHandler.getPrimaryPhp(),
-			php,
-			'/wordpress'
-		);
+		proxyFileSystem(await requestHandler.getPrimaryPhp(), php, [
+			'/tmp',
+			requestHandler.documentRoot,
+			'/internal/mu-plugins',
+		]);
 	}
 
 	// php.setSpawnHandler(spawnHandlerFactory(processManager));
 	// Rotate the PHP runtime periodically to avoid memory leak-related crashes.
 	// @see https://github.com/WordPress/wordpress-playground/pull/990 for more context
 	rotatePHPRuntime({
 		php,
-		cwd: '/wordpress',
+		cwd: requestHandler.documentRoot,
 		recreateRuntime: createPhpRuntime,
 		maxRequests: 400,
 	});
 	return php;
 }
 
-/**
- * Share the parent's MEMFS instance with the child process.
- * Only mount the document root and the /tmp directory,
- * the rest of the filesystem (like the devices) should be
- * private to each PHP instance.
- *
- * @TODO: Ship this feature in the php-wasm library. It
- *        will be commonly used in multi-instance Playground
- *        applications. The website app does something similar,
- *        and so will wp-now, VSCode, etc.
- */
-export function proxyFileSystem(
-	sourceOfTruth: BasePHP,
-	replica: BasePHP,
-	documentRoot: string
-) {
-	// We can't just import the symbol from the library because
-	// Playground CLI is built as ESM and php-wasm-node is built as
-	// CJS and the imported symbols will different in the production build.
-	const __private__symbol = Object.getOwnPropertySymbols(sourceOfTruth)[0];
-	for (const path of [documentRoot, '/tmp']) {
-		if (!replica.fileExists(path)) {
-			replica.mkdir(path);
-		}
-		if (!sourceOfTruth.fileExists(path)) {
-			sourceOfTruth.mkdir(path);
-		}
-		// @ts-ignore
-		replica[__private__symbol].FS.mount(
-			// @ts-ignore
-			replica[__private__symbol].PROXYFS,
-			{
-				root: path,
-				// @ts-ignore
-				fs: sourceOfTruth[__private__symbol].FS,
-			},
-			path
-		);
-	}
-}
-
 /**
  * @TODO: Ship this feature in the php-wasm library.
  *