Use file descriptor 0 or /dev/tty to read stdin

On Linux, when Node.js (at least, v15.2.0) does a readFileSync of
/dev/tty, it hangs.

The addition of /dev/tty comes from 9bcf45b,
which converts to ESM.
It also switches from reading /dev/stdin, to:

1. on Windows, reading file descriptor 0;
2. on other platforms, reading /dev/tty
   (which presumably works on macOS, but not Linux).

However, based on the [Node.js documentation][fd0],
reading file descriptor 0 always reads stdin on all platforms,
thanks to a compatibility layer in Node.js.

Subtly, for Linux specifically, using /dev/stdin
instead of the zero file descriptor, enables the following use-case:
just enter `commonmark` on the console, causing it to wait for prompt.
You can then type text followed by Control-D
to have that text be the input.

    | File       | Linux           | macOS           | Windows   |
    |============|=================|=================|===========|
    |   |  Pipe  | ✓               | ✓               | ✓         |
    | 0 |--------|-----------------|-----------------|-----------|
    |   | Prompt | EAGAIN          | EAGAIN          | TypeError |
    |~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~|~~~~~~~~~~~|
    |            | ✓               | ✓               | ENOENT    |
    | /dev/stdin |-----------------|-----------------|-----------|
    |            | ✓               | EAGAIN          | ENOENT    |
    |~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~|~~~~~~~~~~~|
    |            | (input ignored) | (input ignored) | ENOENT    |
    | /dev/tty   |-----------------|-----------------|-----------|
    |            | ✓               | ✓               | ENOENT    |

Thus we split the decision in a platform-independent way:

1. When in a TTY situation, use /dev/tty.
   Except on Windows, which does not have a PTY,
   so we manually read lines until we hit ^Z (which is EOF on Windows).
2. Otherwise, use file descriptor 0, which works across all platforms.

[fd0]: https://nodejs.org/api/process.html#process_process_stdin_fd

Author: espadrine

bin/commonmark

@@ -4,6 +4,7 @@
 import util from "util";
 import fs from "fs";
 import os from "os";
+import readline from "readline";
 import * as commonmark from "../lib/index.js";
 var version = require('../package.json').version;
 import parseArgs from "minimist";
@@ -77,11 +78,27 @@ if (format === 'html') {
 }
 
 if (files.length === 0) {
-   if (os.platform() === "win32") {
-     inps.push(fs.readFileSync(0, 'utf-8'));
-   } else {
-     inps.push(fs.readFileSync('/dev/tty', 'utf-8'));
-   }
+  if (process.stdin.isTTY) {
+    if (os.platform() === 'win32') {
+      // Windows does not have a PTY that Node relies on.
+      // Instead, we read lines explicitly, tracking ^Z for EOF.
+      (async () => {
+        const rl = readline.createInterface({ input: process.stdin });
+        let inp = '';
+        for await (const line of rl) {
+          if (line === '\x1a') { break; }
+          inp += line;
+        }
+        const doc = parser.parse(inp);
+        const rendered = renderer.render(doc);
+        if (!options.time) { process.stdout.write(rendered); }
+      })();
+    } else {
+      inps.push(fs.readFileSync('/dev/tty', 'utf-8'));
+    }
+  } else {
+    inps.push(fs.readFileSync(0, 'utf-8'));
+  }
 } else {
   for (i = 0; i < files.length; i++) {
     var file = files[i];