Use custom resolver for Haste requests

Summary:
* Allows custom Metro resolvers specified with `resolver.resolveRequest` to intercept Haste resolution requests.
* Makes [`package.json`-based replacements](https://github.com/defunctzombie/package-browser-field-spec#replace-specific-files---advanced) consistently take precedence over Haste in the default resolver.

These are potentially breaking changes for Metro users who have Haste enabled (though they are likely to be benign in practice).

Reviewed By: GijsWeterings

Differential Revision: D30425668

fbshipit-source-id: 52fc6d38a3c317b962a9f3fd4262b54c89b6f69e

Author: motiz88

docs/Configuration.md

@@ -137,7 +137,7 @@ This option works similarly to how [$NODE_PATHS](https://nodejs.org/api/modules.
 
 Type: `?CustomResolver`
 
-An optional function used to resolve requests. Ignored when the request can be resolved through Haste. Particularly useful for cases where aliases are used. For example:
+An optional function used to resolve requests. Particularly useful for cases where aliases are used. For example:
 
 ```javascript
 resolveRequest: (context, realModuleName, platform, moduleName) => {

packages/metro-resolver/src/__tests__/index-test.js

@@ -378,25 +378,30 @@ describe('resolveRequest', () => {
     );
   });
 
-  it('is not called for Haste packages', () => {
+  it('is called for Haste packages', () => {
     expect(Resolver.resolve(context, 'some-package', null))
       .toMatchInlineSnapshot(`
       Object {
-        "filePath": "/haste/some-package/main.js",
-        "type": "sourceFile",
+        "type": "empty",
       }
     `);
-    expect(resolveRequest).not.toBeCalled();
+    expect(resolveRequest).toBeCalledTimes(1);
+    expect(resolveRequest).toBeCalledWith(
+      context,
+      'some-package',
+      null,
+      'some-package',
+    );
   });
 
-  it('is not called for Haste modules', () => {
+  it('is called for Haste modules', () => {
     expect(Resolver.resolve(context, 'Foo', null)).toMatchInlineSnapshot(`
       Object {
-        "filePath": "/haste/Foo.js",
-        "type": "sourceFile",
+        "type": "empty",
       }
     `);
-    expect(resolveRequest).not.toBeCalled();
+    expect(resolveRequest).toBeCalledTimes(1);
+    expect(resolveRequest).toBeCalledWith(context, 'Foo', null, 'Foo');
   });
 
   it('is called with the platform and redirected module path', () => {
@@ -459,6 +464,26 @@ describe('resolveRequest', () => {
       'does-not-exist',
     );
   });
+
+  it('can forward Haste requests to the standard resolver', () => {
+    resolveRequest.mockImplementation(
+      (ctx, realModuleName, platform, moduleName) => {
+        return Resolver.resolve(
+          {...ctx, resolveRequest: null},
+          moduleName,
+          platform,
+        );
+      },
+    );
+    expect(Resolver.resolve(context, 'Foo', null)).toMatchInlineSnapshot(`
+      Object {
+        "filePath": "/haste/Foo.js",
+        "type": "sourceFile",
+      }
+    `);
+    expect(resolveRequest).toBeCalledTimes(1);
+    expect(resolveRequest).toBeCalledWith(context, 'Foo', null, 'Foo');
+  });
 });
 
 describe('rewriteHasteRequest', () => {

packages/metro-resolver/src/resolve.js

@@ -70,10 +70,7 @@ function resolve(
     return resolveModulePath(context, absPath, platform);
   }
 
-  // The Haste resolution must occur before the custom resolver because we want
-  // to allow overriding imports. It could be part of the custom resolver, but
-  // that's not the case right now.
-  if (context.allowHaste && !isDirectImport) {
+  if (!resolveRequest && context.allowHaste && !isDirectImport) {
     const normalizedName = normalizePath(realModuleName);
     let nameCandidates;
     if (context.rewriteHasteRequest) {

packages/metro/src/DeltaBundler/__tests__/resolver-test.js

@@ -1837,7 +1837,7 @@ let resolver;
         ).toBe(p('/root/node_modules/aPackage/hastePackage-local-override.js'));
       });
 
-      it('ignores package.json replacements for Haste modules', async () => {
+      it('respects package.json replacements for Haste modules', async () => {
         setMockFileSystem({
           node_modules: {
             aPackage: {
@@ -1859,7 +1859,7 @@ let resolver;
             p('/root/node_modules/aPackage/index.js'),
             'hasteModule',
           ),
-        ).toBe(p('/root/hasteModule.js'));
+        ).toBe(p('/root/node_modules/aPackage/hasteModule-local-override.js'));
       });
     });
 
@@ -2022,7 +2022,7 @@ let resolver;
         );
       });
 
-      it('does not override global package resolutions', async () => {
+      it('overrides global package resolutions', async () => {
         setMockFileSystem({
           'index.js': '',
           aPackage: {
@@ -2035,11 +2035,11 @@ let resolver;
         resolver = await createResolver({resolver: {resolveRequest}});
 
         expect(resolver.resolve(p('/root/index.js'), 'aPackage')).toBe(
-          p('/root/aPackage/index.js'),
+          p('/root/overriden.js'),
         );
       });
 
-      it('does not override haste names', async () => {
+      it('overrides haste names', async () => {
         setMockFileSystem({
           'index.js': '',
           'aPackage.js': '@providesModule aPackage',
@@ -2057,7 +2057,7 @@ let resolver;
         });
 
         expect(resolver.resolve(p('/root/index.js'), 'aPackage')).toBe(
-          p('/root/aPackage.js'),
+          p('/root/overriden.js'),
         );
       });
 

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

@@ -301,9 +301,6 @@ class DependencyGraph extends EventEmitter {
     );
     let mapByPlatform = getOrCreate(mapByDirectory, to);
     let modulePath = mapByPlatform.get(platform);
-    if (!modulePath) {
-      modulePath = this._moduleMap.getModule(to, platform, true);
-    }
 
     if (!modulePath) {
       try {