Add unstable_preferTreeFS to use TreeFS without enabling symlinks

Summary:
This allows the use of the new symlink-supporting prefix-tree `FileSystem` implementation, `TreeFS` *without* enabling symlinks.

The main purpose of this is to allow like-for-like performance comparisons of operations at this level - in particular, startup involving assembling the tree, and resolution under the new `exists` implementation.

Because `HasteFS` and `TreeFS` should have identical outputs on regular files, this setting is *not* a cache key component (unlike `resolver.unstable_enableSymlinks`).

Reviewed By: motiz88

Differential Revision: D43539702

fbshipit-source-id: 92639845f42d6c7a3d626de9853c9c360b45367a

Author: robhogan

packages/metro-config/src/__tests__/__snapshots__/loadConfig-test.js.snap

@@ -169,6 +169,7 @@ Object {
       "interval": 30000,
       "timeout": 5000,
     },
+    "unstable_preferTreeFS": false,
     "watchman": Object {
       "deferStates": Array [
         "hg.update",
@@ -347,6 +348,7 @@ Object {
       "interval": 30000,
       "timeout": 5000,
     },
+    "unstable_preferTreeFS": false,
     "watchman": Object {
       "deferStates": Array [
         "hg.update",
@@ -525,6 +527,7 @@ Object {
       "interval": 30000,
       "timeout": 5000,
     },
+    "unstable_preferTreeFS": false,
     "watchman": Object {
       "deferStates": Array [
         "hg.update",
@@ -703,6 +706,7 @@ Object {
       "interval": 30000,
       "timeout": 5000,
     },
+    "unstable_preferTreeFS": false,
     "watchman": Object {
       "deferStates": Array [
         "hg.update",

packages/metro-config/src/configTypes.flow.js

@@ -187,15 +187,16 @@ type SymbolicatorConfigT = {
 
 type WatcherConfigT = {
   additionalExts: $ReadOnlyArray<string>,
-  watchman: {
-    deferStates: $ReadOnlyArray<string>,
-  },
   healthCheck: {
     enabled: boolean,
     interval: number,
     timeout: number,
     filePrefix: string,
   },
+  unstable_preferTreeFS: boolean,
+  watchman: {
+    deferStates: $ReadOnlyArray<string>,
+  },
 };
 
 export type InputConfigT = $Shape<{

packages/metro-config/src/defaults/index.js

@@ -138,15 +138,16 @@ const getDefaultValues = (projectRoot: ?string): ConfigT => ({
   },
   watcher: {
     additionalExts,
-    watchman: {
-      deferStates: ['hg.update'],
-    },
     healthCheck: {
       enabled: false,
       filePrefix: '.metro-health-check',
       interval: 30000,
       timeout: 5000,
     },
+    unstable_preferTreeFS: false,
+    watchman: {
+      deferStates: ['hg.update'],
+    },
   },
   cacheStores: [
     new FileStore({

packages/metro-file-map/src/index.js

@@ -93,17 +93,17 @@ export type InputOptions = $ReadOnly<{
   dependencyExtractor?: ?string,
   hasteImplModulePath?: ?string,
 
+  cacheManagerFactory?: ?CacheManagerFactory,
+  console?: Console,
+  healthCheck: HealthCheckOptions,
+  maxWorkers: number,
   perfLoggerFactory?: ?PerfLoggerFactory,
   resetCache?: ?boolean,
-  maxWorkers: number,
   throwOnModuleCollision?: ?boolean,
+  unstable_preferTreeFS?: ?boolean,
   useWatchman?: ?boolean,
-  watchmanDeferStates?: $ReadOnlyArray<string>,
   watch?: ?boolean,
-  console?: Console,
-  cacheManagerFactory?: ?CacheManagerFactory,
-
-  healthCheck: HealthCheckOptions,
+  watchmanDeferStates?: $ReadOnlyArray<string>,
 }>;
 
 type HealthCheckOptions = $ReadOnly<{
@@ -120,6 +120,7 @@ type InternalOptions = {
   resetCache: ?boolean,
   maxWorkers: number,
   throwOnModuleCollision: boolean,
+  unstable_preferTreeFS: boolean,
   useWatchman: boolean,
   watch: boolean,
   watchmanDeferStates: $ReadOnlyArray<string>,
@@ -312,6 +313,7 @@ export default class HasteMap extends EventEmitter {
       perfLoggerFactory: options.perfLoggerFactory,
       resetCache: options.resetCache,
       throwOnModuleCollision: !!options.throwOnModuleCollision,
+      unstable_preferTreeFS: !!options.unstable_preferTreeFS,
       useWatchman: options.useWatchman == null ? true : options.useWatchman,
       watch: !!options.watch,
       watchmanDeferStates: options.watchmanDeferStates ?? [],
@@ -359,7 +361,10 @@ export default class HasteMap extends EventEmitter {
         const rootDir = this._options.rootDir;
         const fileData = initialData.files;
         this._startupPerfLogger?.point('constructFileSystem_start');
-        const FileSystem = this._options.enableSymlinks ? TreeFS : HasteFS;
+        const useTreeFS =
+          this._options.enableSymlinks || this._options.unstable_preferTreeFS;
+        this._startupPerfLogger?.annotate({bool: {useTreeFS}});
+        const FileSystem = useTreeFS ? TreeFS : HasteFS;
         const fileSystem = new FileSystem({
           files: fileData,
           rootDir,

packages/metro/src/node-haste/DependencyGraph/createHasteMap.js

@@ -90,6 +90,7 @@ function createHasteMap(
     rootDir: config.projectRoot,
     roots: config.watchFolders,
     throwOnModuleCollision: options?.throwOnModuleCollision ?? true,
+    unstable_preferTreeFS: config.watcher.unstable_preferTreeFS,
     useWatchman: config.resolver.useWatchman,
     watch: options?.watch == null ? !ci.isCI : options.watch,
     watchmanDeferStates: config.watcher.watchman.deferStates,