src: fix --diagnostic-dir not working with --heapsnapshot-signal

Fixes: nodejs#47842

src/heap_utils.cc

@@ -454,11 +454,16 @@ void TriggerHeapSnapshot(const FunctionCallbackInfo<Value>& args) {
   auto options = GetHeapSnapshotOptions(args[1]);
 
   if (filename_v->IsUndefined()) {
+    std::string dir = env->options()->diagnostic_dir;
+    if (dir.empty()) {
+      dir = env->GetCwd();
+    }
     DiagnosticFilename name(env, "Heap", "heapsnapshot");
+    std::string filename = dir + kPathSeparator + (*name);
     THROW_IF_INSUFFICIENT_PERMISSIONS(
         env, permission::PermissionScope::kFileSystemWrite, env->GetCwd());
-    if (WriteSnapshot(env, *name, options).IsNothing()) return;
-    if (String::NewFromUtf8(isolate, *name).ToLocal(&filename_v)) {
+    if (WriteSnapshot(env, filename.c_str(), options).IsNothing()) return;
+    if (String::NewFromUtf8(isolate, filename.c_str()).ToLocal(&filename_v)) {
       args.GetReturnValue().Set(filename_v);
     }
     return;

test/sequential/test-diagnostic-dir-heapdump-flag.js

@@ -0,0 +1,49 @@
+'use strict';
+const common = require('../common');
+const tmpdir = require('../common/tmpdir');
+
+if (common.isWindows)
+  common.skip('test not supported on Windows');
+
+const assert = require('assert');
+
+if (process.argv[2] === 'child') {
+  const fs = require('fs');
+  const path = require('path');
+
+  assert.strictEqual(process.listenerCount('SIGUSR2'), 1);
+  process.kill(process.pid, 'SIGUSR2');
+  process.kill(process.pid, 'SIGUSR2');
+
+  // Asynchronously wait for the snapshot. Use an async loop to be a bit more
+  // robust in case platform or machine differences throw off the timing.
+  (function validate() {
+    const files = fs.readdirSync(tmpdir.path);
+
+    if (files.length === 0)
+      return setImmediate(validate);
+
+    assert.strictEqual(files.length, 2);
+
+    for (let i = 0; i < files.length; i++) {
+      assert.match(files[i], /^Heap\..+\.heapsnapshot$/);
+      JSON.parse(fs.readFileSync(path.join(tmpdir.path, files[i])));
+    }
+  })();
+} else {
+  const { spawnSync } = require('child_process');
+
+  tmpdir.refresh();
+  const args = [
+    '--heapsnapshot-signal',
+    'SIGUSR2',
+    '--diagnostic-dir',
+    tmpdir.path,
+    __filename,
+    'child',
+  ];
+  const child = spawnSync(process.execPath, args);
+
+  assert.strictEqual(child.status, 0);
+  assert.strictEqual(child.signal, null);
+}