chore: add captureStderr option to runAsyncBase

Added a `captureStderr` option to `lib/run.js` `runAsyncBase` method
that allows for adding stderr information to thrown errors.

lib/run.js

@@ -12,14 +12,19 @@ function runAsyncBase(cmd, args, {
   ignoreFailure = true,
   spawnArgs,
   input,
-  captureStdout = false
+  captureStdout = false,
+  captureStderr = false
 } = {}) {
   if (cmd instanceof URL) {
     cmd = fileURLToPath(cmd);
   }
   let stdio = 'inherit';
   if (captureStdout || input != null) {
-    stdio = [input == null ? 'inherit' : 'pipe', captureStdout ? 'pipe' : 'inherit', 'inherit'];
+    stdio = [
+      input == null ? 'inherit' : 'pipe',
+      captureStdout ? 'pipe' : 'inherit',
+      captureStderr ? 'pipe' : 'inherit'
+    ];
   }
   return new Promise((resolve, reject) => {
     const opt = Object.assign({
@@ -36,13 +41,22 @@ function runAsyncBase(cmd, args, {
       child.stdout.setEncoding('utf8');
       child.stdout.on('data', (chunk) => { stdout += chunk; });
     }
+    let stderr;
+    if (captureStderr) {
+      stderr = '';
+      child.stderr.setEncoding('utf8');
+      child.stderr.on('data', (chunk) => { stderr += chunk; });
+    }
     child.on('error', reject);
     child.on('close', (code) => {
       if (code !== 0) {
         if (ignoreFailure) {
           return reject(new Error(IGNORE));
         }
         const err = new Error(`${cmd} ${args} failed: ${code}`);
+        if (stderr) {
+          err.stderr = stderr;
+        }
         err.code = code;
         err.messageOnly = true;
         return reject(err);