plugins: Fix "Error: spawn npm ENOENT" error on Windows

On Windows, npm should be invoked as `npm.cmd`, not `npm`. Use a
drop-in replacement for `child_process.spawn()` that does the right
thing on Windows.

src/node/utils/run_cmd.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const childProcess = require('child_process');
+const spawn = require('cross-spawn');
 const log4js = require('log4js');
 const path = require('path');
 const settings = require('./Settings');
@@ -28,14 +28,14 @@ const logLines = (readable, logLineFn) => {
 };
 
 /**
- * Similar to `util.promisify(childProcess.exec)`, except:
+ * Similar to `util.promisify(child_rocess.exec)`, except:
  *   - `cwd` defaults to the Etherpad root directory.
  *   - PATH is prefixed with src/node_modules/.bin so that utilities from installed dependencies
  *     (e.g., npm) are preferred over system utilities.
  *   - Output is passed to logger callback functions by default. See below for details.
  *
  * @param args Array of command-line arguments, where `args[0]` is the command to run.
- * @param opts Optional options that will be passed to `childProcess.spawn()` with two extensions:
+ * @param opts Optional options that will be passed to `child_process.spawn()` with two extensions:
  *   - `stdoutLogger`: Callback that is called each time a line of text is written to stdout (utf8
  *     is assumed). The line (without trailing newline) is passed as the only argument. If null,
  *     stdout is not logged. If unset, defaults to no-op. Ignored if stdout is not a pipe.
@@ -48,7 +48,7 @@ module.exports = exports = (args, opts = {}) => {
   logger.debug(`Executing command: ${args.join(' ')}`);
 
   const {stdoutLogger = () => {}, stderrLogger = () => {}} = opts;
-  // Avoid confusing childProcess.spawn() with our extensions.
+  // Avoid confusing child_process.spawn() with our extensions.
   opts = {...opts}; // Make a copy to avoid mutating the caller's copy.
   delete opts.stdoutLogger;
   delete opts.stderrLogger;
@@ -70,7 +70,7 @@ module.exports = exports = (args, opts = {}) => {
   // process's `exit` handler so that we get a useful stack trace.
   const procFailedErr = new Error(`Command exited non-zero: ${args.join(' ')}`);
 
-  const proc = childProcess.spawn(args[0], args.slice(1), {cwd: settings.root, ...opts, env});
+  const proc = spawn(args[0], args.slice(1), {cwd: settings.root, ...opts, env});
   if (proc.stdout != null && stdoutLogger != null) logLines(proc.stdout, stdoutLogger);
   if (proc.stderr != null && stderrLogger != null) logLines(proc.stderr, stderrLogger);
   const p = new Promise((resolve, reject) => {

src/package-lock.json

@@ -1281,7 +1281,6 @@
       "version": "7.0.3",
       "resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-7.0.3.tgz",
       "integrity": "sha512-iRDPJKUPVEND7dHPO8rkbOnPpyDygcDFtWjpeWNCgy8WP2rXcxXL8TskReQl6OrB2G7+UJrags1q15Fudc7G6w==",
-      "dev": true,
       "requires": {
         "path-key": "^3.1.0",
         "shebang-command": "^2.0.0",
@@ -1292,7 +1291,6 @@
           "version": "2.0.2",
           "resolved": "https://registry.npmjs.org/which/-/which-2.0.2.tgz",
           "integrity": "sha512-BLI3Tl1TW3Pvl70l3yq3Y64i+awpwXqsGBYWkkqMtnbXgrMD+yj7rhW0kuEDxzJaYXGjEW5ogapKNMEKNMjibA==",
-          "dev": true,
           "requires": {
             "isexe": "^2.0.0"
           }
@@ -7097,8 +7095,7 @@
     "path-key": {
       "version": "3.1.1",
       "resolved": "https://registry.npmjs.org/path-key/-/path-key-3.1.1.tgz",
-      "integrity": "sha512-ojmeN0qd+y0jszEtoY48r0Peq5dwMEkIlCOu6Q5f41lfkswXuKtYrhgoTpLnyIcHm24Uhqx+5Tqm2InSwLhE6Q==",
+      "integrity": "sha512-ojmeN0qd+y0jszEtoY48r0Peq5dwMEkIlCOu6Q5f41lfkswXuKtYrhgoTpLnyIcHm24Uhqx+5Tqm2InSwLhE6Q=="
-      "dev": true
     },
     "path-parse": {
       "version": "1.0.6",
@@ -7621,7 +7618,6 @@
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/shebang-command/-/shebang-command-2.0.0.tgz",
       "integrity": "sha512-kHxr2zZpYtdmrN1qDjrrX/Z1rR1kG8Dx+gkpK1G4eXmvXswmcE1hTWBWYUzlraYw1/yZp6YuDY77YtvbN0dmDA==",
-      "dev": true,
       "requires": {
         "shebang-regex": "^3.0.0"
       }
@@ -7629,8 +7625,7 @@
     "shebang-regex": {
       "version": "3.0.0",
       "resolved": "https://registry.npmjs.org/shebang-regex/-/shebang-regex-3.0.0.tgz",
-      "integrity": "sha512-7++dFhtcx3353uBaq8DDR4NuxBetBzC7ZQOhmTQInHEd6bSrXdiEyzCvG07Z44UYdLShWUyXt5M/yhz8ekcb1A==",
+      "integrity": "sha512-7++dFhtcx3353uBaq8DDR4NuxBetBzC7ZQOhmTQInHEd6bSrXdiEyzCvG07Z44UYdLShWUyXt5M/yhz8ekcb1A=="
-      "dev": true
     },
     "signal-exit": {
       "version": "3.0.3",

src/package.json

@@ -36,6 +36,7 @@
     "cheerio": "0.22.0",
     "clean-css": "4.2.3",
     "cookie-parser": "1.4.5",
+    "cross-spawn": "^7.0.3",
     "ejs": "^3.1.6",
     "etherpad-require-kernel": "1.0.9",
     "etherpad-yajsml": "0.0.2",