Add getPackageForModule function to resolution context

Summary:
Exposes an additional accessor on this API in order for `package.json`-based resolution to be relocated into metro-resolver.

Changelog: **[Feature]** Add `getPackageForModule` accessor to custom resolver context

Reviewed By: jacdebug

Differential Revision: D42740236

fbshipit-source-id: 5753b427cd50417a657a59bcd06224aebd7b3fb9

docs/Resolution.md

@@ -168,6 +168,10 @@ The ordered list of fields in `package.json` that should be read to resolve a pa
 
 Given the path to a `package.json` file, returns the parsed file contents.
 
+#### `getPackageForModule: (modulePath: string) => ?PackageInfo`
+
+Given a module path that may exist under an npm package, locates and returns the package root path and parsed `package.json` contents.
+
 #### `resolveHasteModule: string => ?string`
 
 Resolves a Haste module name to an absolute path. Returns `null` if no such module exists.

packages/metro-resolver/src/__tests__/utils.js

@@ -33,6 +33,7 @@ export function createResolutionContext(
     extraNodeModules: null,
     getPackage: (packageJsonPath: string) =>
       JSON.parse(fileMap[packageJsonPath]),
+    getPackageForModule: () => null,
     isAssetFile: () => false,
     mainFields: ['browser', 'main'],
     nodeModulesPaths: [],

packages/metro-resolver/src/types.js

@@ -50,6 +50,11 @@ export type PackageJson = $ReadOnly<{
   ...
 }>;
 
+export type PackageInfo = $ReadOnly<{
+  packageJson: PackageJson,
+  rootPath: string,
+}>;
+
 /**
  * Check existence of a single file.
  */
@@ -91,6 +96,12 @@ export type FileOrDirContext = $ReadOnly<{
    * Get the parsed contents of the specified `package.json` file.
    */
   getPackage: (packageJsonPath: string) => ?PackageJson,
+
+  /**
+   * Get the package information and parsed `package.json` file for for a given
+   * module path, if it is contained within an npm package.
+   */
+  getPackageForModule: (modulePath: string) => ?PackageInfo,
 }>;
 
 export type HasteContext = $ReadOnly<{

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

@@ -20,7 +20,7 @@ import type {
   ResolveAsset,
 } from 'metro-resolver';
 import type {ResolverInputOptions} from '../../shared/types.flow';
-import type {PackageJson} from 'metro-resolver/src/types';
+import type {PackageInfo, PackageJson} from 'metro-resolver/src/types';
 
 const {codeFrameColumns} = require('@babel/code-frame');
 const fs = require('fs');
@@ -220,6 +220,7 @@ class ModuleResolver<TPackage: Packageish> {
           resolveHastePackage: (name: string) =>
             this._options.getHastePackagePath(name, platform),
           getPackage: this._getPackage,
+          getPackageForModule: this._getPackageForModule,
         },
         moduleName,
         platform,
@@ -282,6 +283,24 @@ class ModuleResolver<TPackage: Packageish> {
     return null;
   };
 
+  _getPackageForModule = (modulePath: string): ?PackageInfo => {
+    let pkg;
+
+    try {
+      pkg = this._options.moduleCache.getPackageOf(modulePath);
+    } catch (e) {
+      // Do nothing. The standard module cache does not trigger any error, but
+      // the ModuleGraph one does, if the module does not exist.
+    }
+
+    return pkg != null
+      ? {
+          rootPath: path.dirname(pkg.path),
+          packageJson: pkg.read(),
+        }
+      : null;
+  };
+
   /**
    * TODO: Return Resolution instead of coercing to BundlerResolution here
    */