Adds support for PnP

lib/PnpPlugin.js

@@ -0,0 +1,40 @@
+"use strict";
+
+module.exports = class PnpPlugin {
+	constructor(source, pnpApi, target) {
+		this.source = source;
+		this.pnpApi = pnpApi;
+		this.target = target;
+	}
+
+	apply(resolver) {
+		const target = resolver.ensureHook(this.target);
+		resolver
+			.getHook(this.source)
+			.tapAsync("PnpPlugin", (requestContext, resolveContext, callback) => {
+				const request = requestContext.request;
+
+				// The trailing slash indicates to PnP that this value is a folder rather than a file
+				const issuer = `${requestContext.path}/`;
+
+				let resolution;
+				try {
+					resolution = this.pnpApi.resolveToUnqualified(request, issuer, {
+						considerBuiltins: false
+					});
+				} catch (error) {
+					return callback(error);
+				}
+
+				resolver.doResolve(
+					target,
+					Object.assign({}, requestContext, {
+						request: resolution
+					}),
+					null,
+					resolveContext,
+					callback
+				);
+			});
+	}
+};

lib/ResolverFactory.js

@@ -28,6 +28,7 @@ const AppendPlugin = require("./AppendPlugin");
 const ResultPlugin = require("./ResultPlugin");
 const ModuleAppendPlugin = require("./ModuleAppendPlugin");
 const UnsafeCachePlugin = require("./UnsafeCachePlugin");
+const PnpPlugin = require("./PnpPlugin");
 
 exports.createResolver = function(options) {
 	//// OPTIONS ////
@@ -67,9 +68,23 @@ exports.createResolver = function(options) {
 	// A list of module alias configurations or an object which maps key to value
 	let alias = options.alias || [];
 
+	// A PnP API that should be used - null is "never", undefined is "auto"
+	const pnpApi =
+		typeof options.pnpApi === "undefined"
+			? process.versions.pnp
+				? require("pnpapi") // eslint-disable-line node/no-missing-require
+				: null
+			: options.pnpApi;
+
 	// Resolve symlinks to their symlinked location
 	const symlinks =
-		typeof options.symlinks !== "undefined" ? options.symlinks : true;
+		typeof options.symlinks !== "undefined"
+			? options.symlinks
+			: // PnP currently needs symlinks to be preserved to resolve peer dependencies
+			// Ref: https://github.com/webpack/enhanced-resolve/pull/168/files#r268819172
+			pnpApi
+			? false
+			: true;
 
 	// Resolve to a context instead of a file
 	const resolveToContext = options.resolveToContext || false;
@@ -215,6 +230,7 @@ exports.createResolver = function(options) {
 		plugins.push(new TryNextPlugin("raw-module", null, "module"));
 
 	// module
+	if (pnpApi) plugins.push(new PnpPlugin("before-module", pnpApi, "resolve"));
 	modules.forEach(item => {
 		if (Array.isArray(item))
 			plugins.push(

test/fixtures/pnp/pkg/symlink

@@ -0,0 +1 @@
+dir

test/pnp.js

@@ -0,0 +1,67 @@
+var path = require("path");
+require("should");
+var ResolverFactory = require("../lib/ResolverFactory");
+var NodeJsInputFileSystem = require("../lib/NodeJsInputFileSystem");
+var CachedInputFileSystem = require("../lib/CachedInputFileSystem");
+
+var pnpApi = {
+	mocks: new Map(),
+	resolveToUnqualified(request, issuer) {
+		if (pnpApi.mocks.has(request)) {
+			return pnpApi.mocks.get(request);
+		} else {
+			throw new Error(`No way`);
+		}
+	}
+};
+
+var nodeFileSystem = new CachedInputFileSystem(
+	new NodeJsInputFileSystem(),
+	4000
+);
+
+var resolver = ResolverFactory.createResolver({
+	extensions: [".ts", ".js"],
+	fileSystem: nodeFileSystem,
+	pnpApi
+});
+
+var fixture = path.resolve(__dirname, "fixtures", "pnp");
+
+describe("extensions", function() {
+	it("should resolve by going through the pnp api", function(done) {
+		pnpApi.mocks.set(
+			"pkg/dir/index.js",
+			path.resolve(fixture, "pkg/dir/index.js")
+		);
+		resolver.resolve({}, fixture, "pkg/dir/index.js", {}, function(
+			err,
+			result
+		) {
+			console.log(err);
+			result.should.equal(path.resolve(fixture, "pkg/dir/index.js"));
+			done();
+		});
+	});
+	it("should resolve module names", function(done) {
+		pnpApi.mocks.set("pkg", path.resolve(fixture, "pkg"));
+		resolver.resolve({}, fixture, "pkg", {}, function(err, result) {
+			result.should.equal(path.resolve(fixture, "pkg/index.js"));
+			done();
+		});
+	});
+	it("should not resolve symlinks", function(done) {
+		pnpApi.mocks.set("pkg/symlink", path.resolve(fixture, "pkg/symlink"));
+		resolver.resolve({}, fixture, "pkg/symlink", {}, function(err, result) {
+			result.should.equal(path.resolve(fixture, "pkg/symlink/index.js"));
+			done();
+		});
+	});
+	it("should properly deal with other extensions", function(done) {
+		pnpApi.mocks.set("pkg/typescript", path.resolve(fixture, "pkg/typescript"));
+		resolver.resolve({}, fixture, "pkg/typescript", {}, function(err, result) {
+			result.should.equal(path.resolve(fixture, "pkg/typescript/index.ts"));
+			done();
+		});
+	});
+});