child_process: exit spawnSync with null on signal

This commit sets the spawnSync() exit code to null when the
child is killed via signal. This brings the behavior more in
sync with spawn().

Fixes: https://github.com/nodejs/node/issues/11284
PR-URL: https://github.com/nodejs/node/pull/11288
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>

src/spawn_sync.cc

@@ -650,12 +650,17 @@ Local<Object> SyncProcessRunner::BuildResultObject() {
                    Integer::New(env()->isolate(), GetError()));
   }
 
-  if (exit_status_ >= 0)
-    js_result->Set(env()->status_string(),
-        Number::New(env()->isolate(), static_cast<double>(exit_status_)));
-  else
+  if (exit_status_ >= 0) {
+    if (term_signal_ > 0) {
+      js_result->Set(env()->status_string(), Null(env()->isolate()));
+    } else {
+      js_result->Set(env()->status_string(),
+          Number::New(env()->isolate(), static_cast<double>(exit_status_)));
+    }
+  } else {
     // If exit_status_ < 0 the process was never started because of some error.
     js_result->Set(env()->status_string(), Null(env()->isolate()));
+  }
 
   if (term_signal_ > 0)
     js_result->Set(env()->signal_string(),

test/parallel/test-child-process-spawnsync-kill-signal.js

@@ -1,12 +1,11 @@
 'use strict';
-const common = require('../common');
+require('../common');
 const assert = require('assert');
 const cp = require('child_process');
 
 if (process.argv[2] === 'child') {
   setInterval(() => {}, 1000);
 } else {
-  const exitCode = common.isWindows ? 1 : 0;
   const { SIGKILL } = process.binding('constants').os.signals;
 
   function spawn(killSignal) {
@@ -14,7 +13,7 @@ if (process.argv[2] === 'child') {
                                [__filename, 'child'],
                                {killSignal, timeout: 100});
 
-    assert.strictEqual(child.status, exitCode);
+    assert.strictEqual(child.status, null);
     assert.strictEqual(child.error.code, 'ETIMEDOUT');
     return child;
   }