packager: ResolutionRequest.js: _loadAsDir and _loadAsFile sync

Reviewed By: davidaurelio

Differential Revision: D4754090

fbshipit-source-id: 84ad1d988bf097d3094d90f3738ce64cc523879c

packages/metro-bundler/src/node-haste/DependencyGraph/ResolutionRequest.js

@@ -51,6 +51,22 @@ type Options = {
   preferNativePlatform: boolean,
 };
 
+/**
+ * It may not be a great pattern to leverage exception just for "trying" things
+ * out, notably for performance. We should consider replacing these functions
+ * to be nullable-returning, or being better stucture to the algorithm.
+ */
+function tryResolveSync<T>(action: () => T, secondaryAction: () => T): T {
+  try {
+    return action();
+  } catch (error) {
+    if (error.type !== 'UnableToResolveError') {
+      throw error;
+    }
+    return secondaryAction();
+  }
+}
+
 class ResolutionRequest {
   _dirExists: DirExistsFn;
   _entryPath: string;
@@ -268,7 +284,7 @@ class ResolutionRequest {
           package_.root,
           path.relative(packageName, realModuleName)
         );
-        return this._tryResolve(
+        return tryResolveSync(
           () => this._loadAsFile(
             potentialModulePath,
             fromModule,
@@ -310,7 +326,7 @@ class ResolutionRequest {
           );
         }
 
-        return this._tryResolve(
+        return tryResolveSync(
           () => this._loadAsFile(realModuleName, fromModule, toModuleName),
           () => this._loadAsDir(realModuleName, fromModule, toModuleName)
         );
@@ -371,9 +387,13 @@ class ResolutionRequest {
             p = this._tryResolve(
               () => this._tryResolve(
                 () => p,
+                () => Promise.resolve().then(
                   () => this._loadAsFile(potentialModulePath, fromModule, toModuleName),
                 ),
-              () => this._loadAsDir(potentialModulePath, fromModule, toModuleName)
+              ),
+              () => Promise.resolve().then(
+                () => this._loadAsDir(potentialModulePath, fromModule, toModuleName),
+              ),
             );
           });
 
@@ -398,8 +418,7 @@ class ResolutionRequest {
     }
   }
 
-  _loadAsFile(potentialModulePath: string, fromModule: Module, toModule: string): Promise<Module> {
+  _loadAsFile(potentialModulePath: string, fromModule: Module, toModule: string): Module {
-    return Promise.resolve().then(() => {
     if (this._helpers.isAssetFile(potentialModulePath)) {
       let dirname = path.dirname(potentialModulePath);
       if (!this._dirExists(dirname)) {
@@ -455,11 +474,9 @@ class ResolutionRequest {
     }
 
     return this._moduleCache.getModule(file);
-    });
   }
 
-  _loadAsDir(potentialDirPath: string, fromModule: Module, toModule: string) {
+  _loadAsDir(potentialDirPath: string, fromModule: Module, toModule: string): Module {
-    return Promise.resolve().then(() => {
     if (!this._dirExists(potentialDirPath)) {
       throw new UnableToResolveError(
         fromModule,
@@ -471,7 +488,7 @@ class ResolutionRequest {
     const packageJsonPath = path.join(potentialDirPath, 'package.json');
     if (this._hasteFS.exists(packageJsonPath)) {
       const main = this._moduleCache.getPackage(packageJsonPath).getMain();
-        return this._tryResolve(
+      return tryResolveSync(
         () => this._loadAsFile(main, fromModule, toModule),
         () => this._loadAsDir(main, fromModule, toModule),
       );
@@ -482,7 +499,6 @@ class ResolutionRequest {
       fromModule,
       toModule,
     );
-    });
   }
 
   _resetResolutionCache() {