module: print location of unsettled top-level await in entry points

When the entry point is a module and the graph it imports still
contains unsettled top-level await when the Node.js instance
finishes the event loop, search from the entry point module
for unsettled top-level await and print their location.

To avoid unnecessary overhead, we register a promise that only
gets settled when the entry point graph evaluation returns
from await, and only search the module graph if it's still
unsettled by the time the instance is exiting.

This patch only handles this for entry point modules. Other kinds of
modules are more complicated so will be left for the future.

Drive-by: update the terminology "unfinished promise" to the
more correct one "unsettled promise" in the codebase.

PR-URL: nodejs#51999
Fixes: nodejs#42868
Reviewed-By: Moshe Atlow <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Geoffrey Booth <[email protected]>

doc/api/process.md

@@ -3953,8 +3953,8 @@ cases:
   and generally can only happen during development of Node.js itself.
 * `12` **Invalid Debug Argument**: The `--inspect` and/or `--inspect-brk`
   options were set, but the port number chosen was invalid or unavailable.
-* `13` **Unfinished Top-Level Await**: `await` was used outside of a function
-  in the top-level code, but the passed `Promise` never resolved.
+* `13` **Unsettled Top-Level Await**: `await` was used outside of a function
+  in the top-level code, but the passed `Promise` never settled.
 * `14` **Snapshot Failure**: Node.js was started to build a V8 startup
   snapshot and it failed because certain requirements of the state of
   the application were not met.

lib/internal/modules/esm/hooks.js

@@ -32,7 +32,7 @@ const {
   ERR_METHOD_NOT_IMPLEMENTED,
   ERR_WORKER_UNSERIALIZABLE_ERROR,
 } = require('internal/errors').codes;
-const { exitCodes: { kUnfinishedTopLevelAwait } } = internalBinding('errors');
+const { exitCodes: { kUnsettledTopLevelAwait } } = internalBinding('errors');
 const { URL } = require('internal/url');
 const { canParse: URLCanParse } = internalBinding('url');
 const { receiveMessageOnPort } = require('worker_threads');
@@ -615,7 +615,7 @@ class HooksProxy {
     } while (response == null);
     debug('got sync response from worker', { method, args });
     if (response.message.status === 'never-settle') {
-      process.exit(kUnfinishedTopLevelAwait);
+      process.exit(kUnsettledTopLevelAwait);
     } else if (response.message.status === 'exit') {
       process.exit(response.message.body);
     }

lib/internal/modules/esm/loader.js

@@ -182,7 +182,7 @@ class ModuleLoader {
     }
   }
 
-  async eval(source, url) {
+  async eval(source, url, isEntryPoint = false) {
     const evalInstance = (url) => {
       const { ModuleWrap } = internalBinding('module_wrap');
       const { registerModule } = require('internal/modules/esm/utils');
@@ -201,7 +201,7 @@ class ModuleLoader {
     const job = new ModuleJob(
       this, url, undefined, evalInstance, false, false);
     this.loadCache.set(url, undefined, job);
-    const { module } = await job.run();
+    const { module } = await job.run(isEntryPoint);
 
     return {
       __proto__: null,
@@ -311,9 +311,9 @@ class ModuleLoader {
    *                                                  module import.
    * @returns {Promise<ModuleExports>}
    */
-  async import(specifier, parentURL, importAttributes) {
+  async import(specifier, parentURL, importAttributes, isEntryPoint = false) {
     const moduleJob = await this.getModuleJob(specifier, parentURL, importAttributes);
-    const { module } = await moduleJob.run();
+    const { module } = await moduleJob.run(isEntryPoint);
     return module.getNamespace();
   }
 

lib/internal/modules/esm/module_job.js

@@ -17,10 +17,15 @@ const {
   StringPrototypeIncludes,
   StringPrototypeSplit,
   StringPrototypeStartsWith,
+  globalThis,
 } = primordials;
 
 const { ModuleWrap } = internalBinding('module_wrap');
-
+const {
+  privateSymbols: {
+    entry_point_module_private_symbol,
+  },
+} = internalBinding('util');
 const { decorateErrorStack, kEmptyObject } = require('internal/util');
 const {
   getSourceMapsEnabled,
@@ -213,8 +218,11 @@ class ModuleJob {
     return { __proto__: null, module: this.module };
   }
 
-  async run() {
+  async run(isEntryPoint = false) {
     await this.instantiate();
+    if (isEntryPoint) {
+      globalThis[entry_point_module_private_symbol] = this.module;
+    }
     const timeout = -1;
     const breakOnSigint = false;
     setHasStartedUserESMExecution();

lib/internal/modules/run_main.js

@@ -2,6 +2,7 @@
 
 const {
   StringPrototypeEndsWith,
+  globalThis,
 } = primordials;
 
 const { containsModuleSyntax } = internalBinding('contextify');
@@ -16,9 +17,12 @@ const {
 } = require('internal/process/execution');
 const {
   triggerUncaughtException,
-  exitCodes: { kUnfinishedTopLevelAwait },
 } = internalBinding('errors');
-
+const {
+  privateSymbols: {
+    entry_point_promise_private_symbol,
+  },
+} = internalBinding('util');
 /**
  * Get the absolute path to the main entry point.
  * @param {string} main - Entry point path
@@ -102,20 +106,10 @@ function shouldUseESMLoader(mainPath) {
   return type === 'module';
 }
 
-/**
- * Handle a Promise from running code that potentially does Top-Level Await.
- * In that case, it makes sense to set the exit code to a specific non-zero value
- * if the main code never finishes running.
- */
-function handleProcessExit() {
-  process.exitCode ??= kUnfinishedTopLevelAwait;
-}
-
 /**
  * @param {function(ModuleLoader):ModuleWrap|undefined} callback
  */
 async function asyncRunEntryPointWithESMLoader(callback) {
-  process.on('exit', handleProcessExit);
   const cascadedLoader = require('internal/modules/esm/loader').getOrInitializeCascadedLoader();
   try {
     const userImports = getOptionValue('--import');
@@ -137,8 +131,6 @@ async function asyncRunEntryPointWithESMLoader(callback) {
       err,
       true, /* fromPromise */
     );
-  } finally {
-    process.off('exit', handleProcessExit);
   }
 }
 
@@ -152,6 +144,10 @@ async function asyncRunEntryPointWithESMLoader(callback) {
  */
 function runEntryPointWithESMLoader(callback) {
   const promise = asyncRunEntryPointWithESMLoader(callback);
+  // Register the promise - if by the time the event loop finishes running, this is
+  // still unsettled, we'll search the graph from the entry point module and print
+  // the location of any unsettled top-level await found.
+  globalThis[entry_point_promise_private_symbol] = promise;
   return promise;
 }
 
@@ -171,7 +167,7 @@ function executeUserEntryPoint(main = process.argv[1]) {
     const mainURL = pathToFileURL(mainPath).href;
 
     runEntryPointWithESMLoader((cascadedLoader) => {
-      // Note that if the graph contains unfinished TLA, this may never resolve
+      // Note that if the graph contains unsettled TLA, this may never resolve
       // even after the event loop stops running.
       return cascadedLoader.import(mainURL, undefined, { __proto__: null }, true);
     });
@@ -185,5 +181,4 @@ function executeUserEntryPoint(main = process.argv[1]) {
 module.exports = {
   executeUserEntryPoint,
   runEntryPointWithESMLoader,
-  handleProcessExit,
 };

lib/internal/process/per_thread.js

@@ -173,9 +173,6 @@ function wrapProcessMethods(binding) {
   memoryUsage.rss = rss;
 
   function exit(code) {
-    const { handleProcessExit } = require('internal/modules/run_main');
-    process.off('exit', handleProcessExit);
-
     if (arguments.length !== 0) {
       process.exitCode = code;
     }

src/api/embed_helpers.cc

@@ -73,7 +73,20 @@ Maybe<ExitCode> SpinEventLoopInternal(Environment* env) {
 
   env->PrintInfoForSnapshotIfDebug();
   env->ForEachRealm([](Realm* realm) { realm->VerifyNoStrongBaseObjects(); });
-  return EmitProcessExitInternal(env);
+  Maybe<ExitCode> exit_code = EmitProcessExitInternal(env);
+  if (exit_code.FromMaybe(ExitCode::kGenericUserError) !=
+      ExitCode::kNoFailure) {
+    return exit_code;
+  }
+
+  auto unsettled_tla = env->CheckUnsettledTopLevelAwait();
+  if (unsettled_tla.IsNothing()) {
+    return Nothing<ExitCode>();
+  }
+  if (!unsettled_tla.FromJust()) {
+    return Just(ExitCode::kUnsettledTopLevelAwait);
+  }
+  return Just(ExitCode::kNoFailure);
 }
 
 struct CommonEnvironmentSetup::Impl {

src/env-inl.h

@@ -371,6 +371,10 @@ inline void Environment::set_exiting(bool value) {
   exit_info_[kExiting] = value ? 1 : 0;
 }
 
+inline bool Environment::exiting() const {
+  return exit_info_[kExiting] == 1;
+}
+
 inline ExitCode Environment::exit_code(const ExitCode default_code) const {
   return exit_info_[kHasExitCode] == 0
              ? default_code

src/env.cc

@@ -4,6 +4,7 @@
 #include "debug_utils-inl.h"
 #include "diagnosticfilename-inl.h"
 #include "memory_tracker-inl.h"
+#include "module_wrap.h"
 #include "node_buffer.h"
 #include "node_context_data.h"
 #include "node_contextify.h"
@@ -50,6 +51,7 @@ using v8::HeapSpaceStatistics;
 using v8::Integer;
 using v8::Isolate;
 using v8::Local;
+using v8::Maybe;
 using v8::MaybeLocal;
 using v8::NewStringType;
 using v8::Number;
@@ -1228,6 +1230,41 @@ void Environment::AtExit(void (*cb)(void* arg), void* arg) {
   at_exit_functions_.push_front(ExitCallback{cb, arg});
 }
 
+Maybe<bool> Environment::CheckUnsettledTopLevelAwait() {
+  HandleScope scope(isolate_);
+  Local<Context> ctx = context();
+  Local<Value> value;
+
+  Local<Value> entry_point_promise;
+  if (!ctx->Global()
+           ->GetPrivate(ctx, entry_point_promise_private_symbol())
+           .ToLocal(&entry_point_promise)) {
+    return v8::Nothing<bool>();
+  }
+  if (!entry_point_promise->IsPromise()) {
+    return v8::Just(true);
+  }
+  if (entry_point_promise.As<Promise>()->State() !=
+      Promise::PromiseState::kPending) {
+    return v8::Just(true);
+  }
+
+  if (!ctx->Global()
+           ->GetPrivate(ctx, entry_point_module_private_symbol())
+           .ToLocal(&value)) {
+    return v8::Nothing<bool>();
+  }
+  if (!value->IsObject()) {
+    return v8::Just(true);
+  }
+  Local<Object> object = value.As<Object>();
+  CHECK(BaseObject::IsBaseObject(isolate_data_, object));
+  CHECK_EQ(object->InternalFieldCount(),
+           loader::ModuleWrap::kInternalFieldCount);
+  auto* wrap = BaseObject::FromJSObject<loader::ModuleWrap>(object);
+  return wrap->CheckUnsettledTopLevelAwait();
+}
+
 void Environment::RunAndClearInterrupts() {
   while (native_immediates_interrupts_.size() > 0) {
     NativeImmediateQueue queue;

src/env.h

@@ -735,6 +735,7 @@ class Environment : public MemoryRetainer {
   // a pseudo-boolean to indicate whether the exit code is undefined.
   inline AliasedInt32Array& exit_info();
   inline void set_exiting(bool value);
+  bool exiting() const;
   inline ExitCode exit_code(const ExitCode default_code) const;
 
   // This stores whether the --abort-on-uncaught-exception flag was passed
@@ -840,6 +841,7 @@ class Environment : public MemoryRetainer {
   void AtExit(void (*cb)(void* arg), void* arg);
   void RunAtExitCallbacks();
 
+  v8::Maybe<bool> CheckUnsettledTopLevelAwait();
   void RunWeakRefCleanup();
 
   v8::MaybeLocal<v8::Value> RunSnapshotSerializeCallback() const;

src/env_properties.h

@@ -24,6 +24,8 @@
   V(transfer_mode_private_symbol, "node:transfer_mode")                        \
   V(host_defined_option_symbol, "node:host_defined_option_symbol")             \
   V(js_transferable_wrapper_private_symbol, "node:js_transferable_wrapper")    \
+  V(entry_point_module_private_symbol, "node:entry_point_module")              \
+  V(entry_point_promise_private_symbol, "node:entry_point_promise")            \
   V(napi_type_tag, "node:napi:type_tag")                                       \
   V(napi_wrapper, "node:napi:wrapper")                                         \
   V(untransferable_object_private_symbol, "node:untransferableObject")         \

src/module_wrap.cc

@@ -104,6 +104,44 @@ ModuleWrap* ModuleWrap::GetFromModule(Environment* env,
   return nullptr;
 }
 
+v8::Maybe<bool> ModuleWrap::CheckUnsettledTopLevelAwait() {
+  Isolate* isolate = env()->isolate();
+  Local<Context> context = env()->context();
+
+  // This must be invoked when the environment is shutting down, and the module
+  // is kept alive by the module wrap via an internal field.
+  CHECK(env()->exiting());
+  CHECK(!module_.IsEmpty());
+
+  Local<Module> module = module_.Get(isolate);
+  // It's a synthetic module, likely a facade wrapping CJS.
+  if (!module->IsSourceTextModule()) {
+    return v8::Just(true);
+  }
+
+  if (!module->IsGraphAsync()) {  // There is no TLA, no need to check.
+    return v8::Just(true);
+  }
+  auto stalled = module->GetStalledTopLevelAwaitMessage(isolate);
+  if (stalled.size() == 0) {
+    return v8::Just(true);
+  }
+
+  if (env()->options()->warnings) {
+    for (auto pair : stalled) {
+      Local<v8::Message> message = std::get<1>(pair);
+
+      std::string reason = "Warning: Detected unsettled top-level await at ";
+      std::string info =
+          FormatErrorMessage(isolate, context, "", message, true);
+      reason += info;
+      FPrintF(stderr, "%s\n", reason);
+    }
+  }
+
+  return v8::Just(false);
+}
+
 // new ModuleWrap(url, context, source, lineOffset, columnOffset)
 // new ModuleWrap(url, context, exportNames, syntheticExecutionFunction)
 void ModuleWrap::New(const FunctionCallbackInfo<Value>& args) {

src/module_wrap.h

@@ -58,6 +58,7 @@ class ModuleWrap : public BaseObject {
   }
 
   v8::Local<v8::Context> context() const;
+  v8::Maybe<bool> CheckUnsettledTopLevelAwait();
 
   SET_MEMORY_INFO_NAME(ModuleWrap)
   SET_SELF_SIZE(ModuleWrap)

src/node_exit_code.h

@@ -27,7 +27,7 @@ namespace node {
   /* This was intended for invalid inspector arguments but is actually now */  \
   /* just a duplicate of InvalidCommandLineArgument */                         \
   V(InvalidCommandLineArgument2, 12)                                           \
-  V(UnfinishedTopLevelAwait, 13)                                               \
+  V(UnsettledTopLevelAwait, 13)                                                \
   V(StartupSnapshotFailure, 14)                                                \
   /* If the process exits from unhandled signals e.g. SIGABRT, SIGTRAP, */     \
   /* typically the exit codes are 128 + signal number. We also exit with */    \