Fix: Fix yarn global prefix directory (#3721)

**Sumary**

Refs #2064.

Uses `%LOCALAPPDATA%\Yarn\bin` and `/usr/local/bin` on POSIX systems if it's writeable, falling back to `~/.yarn/bin` if it is not.

**Test plan**

N/A. Should add automated tests.

__tests__/commands/global.js

@@ -24,11 +24,7 @@ const runGlobal = buildRun.bind(
 );
 
 function getGlobalPath(prefix, name): string {
-  if (process.platform === 'win32') {
-    return path.join(prefix, name);
-  } else {
-    return path.join(prefix, 'bin', name);
-  }
+  return path.join(prefix, 'bin', name);
 }
 
 function getTempGlobalFolder(): string {

src/cli/commands/create.js

@@ -26,7 +26,7 @@ export async function run(config: Config, reporter: Reporter, flags: Object, arg
 
   await runGlobal(config, reporter, {}, ['add', packageName]);
 
-  const binFolder = getBinFolder(config, {});
+  const binFolder = await getBinFolder(config, {});
   const command = path.resolve(binFolder, path.basename(commandName));
 
   await child.spawn(command, [...rest], {stdio: `inherit`, shell: true});

src/cli/commands/global.js

@@ -14,8 +14,11 @@ import {run as runRemove} from './remove.js';
 import {run as runUpgrade} from './upgrade.js';
 import {run as runUpgradeInteractive} from './upgrade-interactive.js';
 import {linkBin} from '../../package-linker.js';
+import {POSIX_GLOBAL_PREFIX, FALLBACK_GLOBAL_PREFIX} from '../../constants.js';
 import * as fs from '../../util/fs.js';
 
+const nativeFs = require('fs');
+
 class GlobalAdd extends Add {
   maybeOutputSaveTree(): Promise<void> {
     for (const pattern of this.addedPatterns) {
@@ -69,44 +72,44 @@ async function getBins(config: Config): Promise<Set<string>> {
   return paths;
 }
 
-function getGlobalPrefix(config: Config, flags: Object): string {
+async function getGlobalPrefix(config: Config, flags: Object): Promise<string> {
   if (flags.prefix) {
     return flags.prefix;
   } else if (config.getOption('prefix')) {
     return String(config.getOption('prefix'));
   } else if (process.env.PREFIX) {
     return process.env.PREFIX;
-  } else if (process.platform === 'win32') {
+  }
+
+  let prefix = FALLBACK_GLOBAL_PREFIX;
+  if (process.platform === 'win32') {
+    // %LOCALAPPDATA%\Yarn --> C:\Users\Alice\AppData\Local\Yarn
     if (process.env.LOCALAPPDATA) {
-      return path.join(process.env.LOCALAPPDATA, 'Yarn', 'bin');
+      prefix = path.join(process.env.LOCALAPPDATA, 'Yarn');
     }
-    // c:\node\node.exe --> prefix=c:\node\
-    return path.dirname(process.execPath);
   } else {
-    // /usr/local/bin/node --> prefix=/usr/local
-    let prefix = path.dirname(path.dirname(process.execPath));
-
-    // destdir only is respected on Unix
-    if (process.env.DESTDIR) {
-      prefix = path.join(process.env.DESTDIR, prefix);
+    prefix = POSIX_GLOBAL_PREFIX;
+  }
+  try {
+    await fs.access(path.join(prefix, 'bin'), (nativeFs.constants || nativeFs).W_OK);
+  } catch (err) {
+    if (err.code === 'EACCES') {
+      prefix = FALLBACK_GLOBAL_PREFIX;
+    } else {
+      throw err;
     }
-
-    return prefix;
   }
+  return prefix;
 }
 
-export function getBinFolder(config: Config, flags: Object): string {
-  const prefix = getGlobalPrefix(config, flags);
-  if (process.platform === 'win32') {
-    return prefix;
-  } else {
-    return path.resolve(prefix, 'bin');
-  }
+export async function getBinFolder(config: Config, flags: Object): Promise<string> {
+  const prefix = await getGlobalPrefix(config, flags);
+  return path.resolve(prefix, 'bin');
 }
 
 async function initUpdateBins(config: Config, reporter: Reporter, flags: Object): Promise<() => Promise<void>> {
   const beforeBins = await getBins(config);
-  const binFolder = getBinFolder(config, flags);
+  const binFolder = await getBinFolder(config, flags);
 
   function throwPermError(err: Error & {[code: string]: string}, dest: string) {
     if (err.code === 'EACCES') {
@@ -205,8 +208,8 @@ const {run, setFlags: _setFlags} = buildSubCommands('global', {
     await updateBins();
   },
 
-  bin(config: Config, reporter: Reporter, flags: Object, args: Array<string>) {
-    reporter.log(getBinFolder(config, flags));
+  async bin(config: Config, reporter: Reporter, flags: Object, args: Array<string>): Promise<void> {
+    reporter.log(await getBinFolder(config, flags));
   },
 
   async ls(config: Config, reporter: Reporter, flags: Object, args: Array<string>): Promise<void> {

src/cli/commands/link.js

@@ -63,7 +63,7 @@ export async function run(config: Config, reporter: Reporter, flags: Object, arg
       // If there is a `bin` defined in the package.json,
       // link each bin to the global bin
       if (manifest.bin) {
-        const globalBinFolder = getGlobalBinFolder(config, flags);
+        const globalBinFolder = await getGlobalBinFolder(config, flags);
         for (const binName in manifest.bin) {
           const binSrc = manifest.bin[binName];
           const binSrcLoc = path.join(linkLoc, binSrc);

src/cli/commands/unlink.js

@@ -40,7 +40,7 @@ export async function run(config: Config, reporter: Reporter, flags: Object, arg
       // If there is a `bin` defined in the package.json,
       // link each bin to the global bin
       if (manifest.bin) {
-        const globalBinFolder = getGlobalBinFolder(config, flags);
+        const globalBinFolder = await getGlobalBinFolder(config, flags);
         for (const binName in manifest.bin) {
           const binDestLoc = path.join(globalBinFolder, binName);
           if (await fs.exists(binDestLoc)) {

src/constants.js

@@ -59,6 +59,9 @@ export const CONFIG_DIRECTORY = getDirectory('config');
 export const LINK_REGISTRY_DIRECTORY = path.join(CONFIG_DIRECTORY, 'link');
 export const GLOBAL_MODULE_DIRECTORY = path.join(CONFIG_DIRECTORY, 'global');
 
+export const POSIX_GLOBAL_PREFIX = '/usr/local';
+export const FALLBACK_GLOBAL_PREFIX = path.join(userHome, '.yarn');
+
 export const META_FOLDER = '.yarn-meta';
 export const INTEGRITY_FILENAME = '.yarn-integrity';
 export const LOCKFILE_FILENAME = 'yarn.lock';

src/util/execute-lifecycle-script.js

@@ -144,7 +144,7 @@ export async function executeLifecycleScript(
 
   // Add global bin folder if it is not present already, as some packages depend
   // on a globally-installed version of node-gyp.
-  const globalBin = getGlobalBinFolder(config, {});
+  const globalBin = await getGlobalBinFolder(config, {});
   if (pathParts.indexOf(globalBin) === -1) {
     pathParts.unshift(globalBin);
   }