add support for Yarn PnP

fixes #168 Co-authored-by: Maël Nison <nison.mael@gmail.com>

Author: sokra

lib/PnpPlugin.js

@@ -0,0 +1,56 @@
+/*
+MIT License http://www.opensource.org/licenses/mit-license.php
+Author Maël Nison @arcanis
+*/
+
+"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", (request, resolveContext, callback) => {
+const req = request.request;
+
+// The trailing slash indicates to PnP that this value is a folder rather than a file
+const issuer = `${request.path}/`;
+
+let resolution;
+try {
+resolution = this.pnpApi.resolveToUnqualified(req, issuer, {
+considerBuiltins: false
+});
+} catch (error) {
+return callback(error);
+}
+
+if (resolution === req) return callback();
+
+const obj = {
+...request,
+path: resolution,
+request: undefined,
+ignoreSymlinks: true
+};
+resolver.doResolve(
+target,
+obj,
+`resolved by pnp to ${resolution}`,
+resolveContext,
+(err, result) => {
+if (err) return callback(err);
+if (result) return callback(null, result);
+// Skip alternatives
+return callback(null, null);
+}
+);
+});
+}
+};

lib/ResolverFactory.js

@@ -28,6 +28,7 @@ const UseFilePlugin = require("./UseFilePlugin");
 const AppendPlugin = require("./AppendPlugin");
 const ResultPlugin = require("./ResultPlugin");
 const UnsafeCachePlugin = require("./UnsafeCachePlugin");
+const PnpPlugin = require("./PnpPlugin");
 
 exports.createResolver = function(options) {
 //// OPTIONS ////
@@ -61,6 +62,15 @@ 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 =
+options.pnpApi === undefined
+? process.versions.pnp
+? // eslint-disable-next-line node/no-missing-require
+ require("pnpapi")
+: null
+: options.pnpApi;
+
 // Resolve symlinks to their symlinked location
 const symlinks =
 typeof options.symlinks !== "undefined" ? options.symlinks : true;
@@ -203,6 +213,9 @@ exports.createResolver = function(options) {
 plugins.push(new JoinRequestPlugin("after-described-resolve", "relative"));
 
 // module
+if (pnpApi) {
+plugins.push(new PnpPlugin("raw-module", pnpApi, "relative"));
+}
 modules.forEach(item => {
 if (Array.isArray(item))
 plugins.push(
@@ -328,7 +341,8 @@ exports.createResolver = function(options) {
 plugins.push(new FileExistsPlugin("file", "existing-file"));
 
 // existing-file
-if (symlinks) plugins.push(new SymlinkPlugin("existing-file", "relative"));
+if (symlinks)
+plugins.push(new SymlinkPlugin("existing-file", "existing-file"));
 plugins.push(new NextPlugin("existing-file", "resolved"));
 }
 

lib/SymlinkPlugin.js

@@ -20,6 +20,7 @@ module.exports = class SymlinkPlugin {
 resolver
 .getHook(this.source)
 .tapAsync("SymlinkPlugin", (request, resolveContext, callback) => {
+if (request.ignoreSymlinks) return callback();
 const pathsResult = getPaths(request.path);
 const pathSeqments = pathsResult.seqments;
 const paths = pathsResult.paths;

test/fixtures/pnp/pkg/dir/index.js

@@ -0,0 +1,7 @@
+{
+ "main": "main.js",
+ "browser": {
+ "./package-alias/index.js": "./package-alias/browser.js",
+ "module": "pkg/dir/index"
+ }
+}