Ensure that /dev/fd, /dev/mqueue and friends exist

It would be very nice, of course, if the MSYS2 runtime emulated these
entries automagically, i.e. without them having to exist on disk.

In the meantime, though, let's just create those entries on disk, just
like Git for Windows' installer does.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.vscode/settings.json

@@ -13,10 +13,12 @@
         "artifactsize",
         "autodrain",
         "Backoff",
+        "mqueue",
         "MSYSTEM",
         "Pacman",
         "unzipper",
-        "vercel"
+        "vercel",
+        "winsymlinks"
     ],
     "git.ignoreLimitWarning": true
 }

__tests__/main.test.ts

@@ -58,5 +58,15 @@ if (process.env.RUN_NETWORK_TESTS !== 'true') {
     expect(
       statSync.bind(null, `${outputDirectory}/mingw64/bin/gcc.exe`)
     ).not.toThrow()
+
+    const hello = child_process.spawnSync(
+      'usr\\bin\\bash.exe',
+      ['-lc', 'cat <(echo hello)'],
+      {
+        cwd: outputDirectory
+      }
+    )
+    expect(hello.stderr.toString()).toBe('')
+    expect(hello.stdout.toString()).toBe('hello\n')
   })
 }

main.ts

@@ -1,7 +1,8 @@
 import * as core from '@actions/core'
+import {get, mkdirp} from './src/downloader'
 import {restoreCache, saveCache} from '@actions/cache'
-import {get} from './src/downloader'
 import process from 'process'
+import {spawnSync} from 'child_process'
 
 async function run(): Promise<void> {
   try {
@@ -80,6 +81,29 @@ async function run(): Promise<void> {
     ) {
       core.exportVariable('LC_CTYPE', 'C.UTF-8')
     }
+
+    // ensure that /dev/fd/*, /dev/mqueue and friends exist
+    for (const path of ['/dev/mqueue', '/dev/shm']) {
+      mkdirp(`${outputDirectory}${path}`)
+    }
+
+    const ln = (linkPath: string, target: string): void => {
+      const child = spawnSync('ln.exe', ['-s', target, linkPath], {
+        cwd: outputDirectory,
+        env: {
+          MSYS: 'winsymlinks:sys'
+        }
+      })
+      if (child.error) throw child.error
+    }
+    for (const [linkPath, target] of Object.entries({
+      fd: 'fd',
+      stdin: 'fd/0',
+      stdout: 'fd/1',
+      stderr: 'fd/2'
+    })) {
+      ln(`/dev/${linkPath}`, `/proc/self/${target}`)
+    }
   } catch (error) {
     core.setFailed(error instanceof Error ? error.message : `${error}`)
   }

src/downloader.ts

@@ -19,7 +19,7 @@ async function fetchJSONFromURL<T>(url: string): Promise<T> {
   return (await res.json()) as T
 }
 
-function mkdirp(directoryPath: string): void {
+export function mkdirp(directoryPath: string): void {
   try {
     const stat = fs.statSync(directoryPath)
     if (stat.isDirectory()) {