Support Windows paths for pnp.

CHANGELOG.md

@@ -4,6 +4,10 @@ Please add one entry in this file for each change in Yarn's behavior. Use the sa
 
 ## Master
 
+- Adds initial support for PnP on Windows
+
+  [#6447](https://github.com/yarnpkg/yarn/pull/6447) - [**John-David Dalton**](https://twitter.com/jdalton)
+
 - Adds a special logic to PnP for ESLint compatibility (temporary, until [eslint/eslint#10125](https://github.com/eslint/eslint/issues/10125) is fixed)
 
   [#6449](https://github.com/yarnpkg/yarn/pull/6449) - [**Maël Nison**](https://twitter.com/arcanis)

src/config.js

@@ -396,11 +396,16 @@ export default class Config {
     }
 
     if (process.platform === 'win32') {
-      if (this.plugnplayEnabled) {
-        this.reporter.warn(this.reporter.lang('plugnplayWindowsSupport'));
+      const cacheRootFolderDrive = path.parse(this._cacheRootFolder).root;
+      const lockfileFolderDrive = path.parse(this.lockfileFolder).root;
+
+      if (cacheRootFolderDrive !== lockfileFolderDrive) {
+        if (this.plugnplayEnabled) {
+          this.reporter.warn(this.reporter.lang('plugnplayWindowsSupport'));
+        }
+        this.plugnplayEnabled = false;
+        this.plugnplayPersist = false;
       }
-      this.plugnplayEnabled = false;
-      this.plugnplayPersist = false;
     }
 
     this.plugnplayShebang = String(this.getOption('plugnplay-shebang') || '') || '/usr/bin/env node';

src/reporters/lang/en.js

@@ -357,8 +357,7 @@ const messages = {
 
   unplugDisabled: "Packages can only be unplugged when Plug'n'Play is enabled.",
 
-  plugnplayWindowsSupport:
-    "Plug'n'Play is ignored on Windows for now - contributions welcome! https://github.com/yarnpkg/yarn/issues/6402",
+  plugnplayWindowsSupport: "Plug'n'Play on Windows doesn't support the cache and project to be kept on separate drives",
 
   packageInstalledWithBinaries: 'Installed $0 with binaries:',
   packageHasBinaries: '$0 has binaries:',

src/util/generate-pnp-map-api.tpl.js

@@ -22,15 +22,18 @@ const blacklistedLocator = {name: NaN, reference: NaN};
 const patchedModules = new Map();
 const fallbackLocators = [topLevelLocator];
 
-// Splits a require request into its components, or return null if the request is a file path
-const pathRegExp = /^(?!\.{0,2}(?:\/|$))((?:@[^\/]+\/)?[^\/]+)\/?(.*|)$/;
+// Matches backslashes of Windows paths
+const backwardSlashRegExp = /\\/g;
+
+// Matches if the path must point to a directory (ie ends with /)
+const isDirRegExp = /\/$/;
 
 // Matches if the path starts with a valid path qualifier (./, ../, /)
 // eslint-disable-next-line no-unused-vars
 const isStrictRegExp = /^\.{0,2}\//;
 
-// Matches if the path must point to a directory (ie ends with /)
-const isDirRegExp = /\/$/;
+// Splits a require request into its components, or return null if the request is a file path
+const pathRegExp = /^(?!\.{0,2}(?:\/|$))((?:@[^\/]+\/)?[^\/]+)\/?(.*|)$/;
 
 // Keep a reference around ("module" is a common name in this context, so better rename it to something more significant)
 const pnpModule = module;
@@ -229,6 +232,15 @@ function makeFakeModule(path) {
   return fakeModule;
 }
 
+/**
+ * Normalize path to posix format.
+ */
+
+// eslint-disable-next-line no-unused-vars
+function normalizePath(fsPath) {
+  return process.platform === 'win32' ? fsPath.replace(backwardSlashRegExp, '/') : fsPath;
+}
+
 /**
  * Forward the resolution to the next resolver (usually the native one)
  */

src/util/generate-pnp-map.js

@@ -11,6 +11,8 @@ const crypto = require('crypto');
 const invariant = require('invariant');
 const path = require('path');
 
+const backwardSlashRegExp = /\\/g;
+
 const OFFLINE_CACHE_EXTENSION = `.zip`;
 
 type PackageInformation = {|
@@ -100,7 +102,7 @@ function generateFindPackageLocator(packageInformationStores: PackageInformation
 
   // Generate a function that, given a file path, returns the associated package name
   code += `exports.findPackageLocator = function findPackageLocator(location) {\n`;
-  code += `  let relativeLocation = path.relative(__dirname, location);\n`;
+  code += `  let relativeLocation = normalizePath(path.relative(__dirname, location));\n`;
   code += `\n`;
   code += `  if (!relativeLocation.match(isStrictRegExp))\n`;
   code += `    relativeLocation = \`./\${relativeLocation}\`;\n`;
@@ -136,7 +138,7 @@ async function getPackageInformationStores(
   const blacklistedLocations: Set<string> = new Set();
 
   const getCachePath = (fsPath: string) => {
-    const cacheRelativePath = path.relative(config.cacheFolder, fsPath);
+    const cacheRelativePath = normalizePath(path.relative(config.cacheFolder, fsPath));
 
     // if fsPath is not inside cacheRelativePath, we just skip it
     if (cacheRelativePath.match(/^\.\.\//)) {
@@ -164,8 +166,12 @@ async function getPackageInformationStores(
     return path.resolve(offlineCacheFolder, `${cacheEntry}${OFFLINE_CACHE_EXTENSION}`, internalPath.join('/'));
   };
 
+  const normalizePath = (fsPath: string) => {
+    return process.platform === 'win32' ? fsPath.replace(backwardSlashRegExp, '/') : fsPath;
+  };
+
   const normalizeDirectoryPath = (fsPath: string) => {
-    let relativePath = path.relative(targetDirectory, resolveOfflineCacheFolder(fsPath));
+    let relativePath = normalizePath(path.relative(targetDirectory, resolveOfflineCacheFolder(fsPath)));
 
     if (!relativePath.match(/^\.{0,2}\//)) {
       relativePath = `./${relativePath}`;