module: unflag Top-Level Await

This unflags Top-Level await so it can be used by default in the module goal. This is accomplished by manually setting the --harmony-top-level-await flag. We are allowing this as a one of approval based on circumstances. It is not a precedent that future harmony features will be manually enabled. Refs: #34551 PR-URL: #34558 Reviewed-By: Mary Marchini <oss@mmarchini.me> Reviewed-By: Zeyu Yang <himself65@outlook.com> Reviewed-By: Gus Caplan <me@gus.host> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com> Reviewed-By: Shelley Vohr <codebytere@gmail.com>
nodejs · Aug 11, 2020 · d0a599a · d0a599a
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diff --git a/doc/api/cli.md b/doc/api/cli.md
@@ -239,16 +239,6 @@ the ability to import a directory that has an index file.
 
 Please see [customizing ESM specifier resolution][] for example usage.
 
-### `--experimental-top-level-await`
-<!-- YAML
-added: v14.3.0
--->
-
-Enable experimental top-level `await` keyword support, available only in ES
-module scripts.
-
-(See also `--experimental-repl-await`.)
-
 ### `--experimental-vm-modules`
 <!-- YAML
 added: v9.6.0

diff --git a/doc/api/esm.md b/doc/api/esm.md
@@ -1146,9 +1146,8 @@ would provide the exports interface for the instantiation of `module.wasm`.
 
 ## Experimental top-level `await`
 
-When the `--experimental-top-level-await` flag is provided, `await` may be used
-in the top level (outside of async functions) within modules. This implements
-the [ECMAScript Top-Level `await` proposal][].
+The `await` keyword may be used in the top level (outside of async functions)
+within modules as per the [ECMAScript Top-Level `await` proposal][].
 
 Assuming an `a.mjs` with
 
@@ -1166,8 +1165,7 @@ console.log(five); // Logs `5`
 ```
 
 ```bash
-node b.mjs # fails
-node --experimental-top-level-await b.mjs # works
+node b.mjs # works
 ```
 
 ## Experimental loaders

diff --git a/doc/node.1 b/doc/node.1
@@ -157,9 +157,6 @@ keyword support in REPL.
 .It Fl -experimental-specifier-resolution
 Select extension resolution algorithm for ES Modules; either 'explicit' (default) or 'node'
 .
-.It Fl -experimental-top-level-await
-Enable experimental top-level await support in ES modules.
-.
 .It Fl -experimental-vm-modules
 Enable experimental ES module support in VM module.
 .

diff --git a/src/node.cc b/src/node.cc
@@ -779,6 +779,13 @@ int ProcessGlobalArgs(std::vector<std::string>* args,
     return 12;
   }
 
+  // TODO(mylesborins): remove this when the harmony-top-level-await flag
+  // is removed in V8
+  if (std::find(v8_args.begin(), v8_args.end(),
+                "--no-harmony-top-level-await") == v8_args.end()) {
+    v8_args.push_back("--harmony-top-level-await");
+  }
+
   auto env_opts = per_process::cli_options->per_isolate->per_env;
   if (std::find(v8_args.begin(), v8_args.end(),
                 "--abort-on-uncaught-exception") != v8_args.end() ||

diff --git a/src/node_options.cc b/src/node_options.cc
@@ -613,12 +613,13 @@ PerIsolateOptionsParser::PerIsolateOptionsParser(
   Implies("--report-signal", "--report-on-signal");
 
   AddOption("--experimental-top-level-await",
-            "enable experimental support for ECMAScript Top-Level Await",
+            "",
             &PerIsolateOptions::experimental_top_level_await,
             kAllowedInEnvironment);
   AddOption("--harmony-top-level-await", "", V8Option{});
   Implies("--experimental-top-level-await", "--harmony-top-level-await");
   Implies("--harmony-top-level-await", "--experimental-top-level-await");
+  ImpliesNot("--no-harmony-top-level-await", "--experimental-top-level-await");
 
   Insert(eop, &PerIsolateOptions::get_per_env_options);
 }

diff --git a/src/node_options.h b/src/node_options.h
@@ -188,7 +188,7 @@ class PerIsolateOptions : public Options {
   bool no_node_snapshot = false;
   bool report_uncaught_exception = false;
   bool report_on_signal = false;
-  bool experimental_top_level_await = false;
+  bool experimental_top_level_await = true;
   std::string report_signal = "SIGUSR2";
   inline EnvironmentOptions* get_per_env_options();
   void CheckOptions(std::vector<std::string>* errors) override;

diff --git a/test/es-module/test-esm-tla.mjs b/test/es-module/test-esm-tla.mjs
@@ -1,5 +1,3 @@
-// Flags: --experimental-top-level-await
-
 import '../common/index.mjs';
 import fixtures from '../common/fixtures.js';
 import assert from 'assert';

diff --git a/test/message/esm_display_syntax_error.mjs b/test/message/esm_display_syntax_error.mjs
@@ -1,2 +1,4 @@
+// Flags: --no-harmony-top-level-await
+
 'use strict';
 await async () => 0;
diff --git a/test/message/esm_display_syntax_error.out b/test/message/esm_display_syntax_error.out
@@ -1,4 +1,4 @@
-file:///*/test/message/esm_display_syntax_error.mjs:2
+file:///*/test/message/esm_display_syntax_error.mjs:4
 await async () => 0;
 ^^^^^
 

diff --git a/test/message/esm_display_syntax_error_module.out b/test/message/esm_display_syntax_error_module.out
@@ -1,6 +1,6 @@
 file:///*/test/fixtures/es-module-loaders/syntax-error.mjs:2
 await async () => 0;
-^^^^^
+^^^^^^^^^^^^^
 
-SyntaxError: Unexpected reserved word
+SyntaxError: Malformed arrow function parameter list
     at Loader.moduleStrategy (internal/modules/esm/translators.js:*:*)
diff --git a/test/message/esm_loader_syntax_error.out b/test/message/esm_loader_syntax_error.out
@@ -2,8 +2,8 @@
 (Use `node --trace-warnings ...` to show where the warning was created)
 file://*/test/fixtures/es-module-loaders/syntax-error.mjs:2
 await async () => 0;
-^^^^^
+^^^^^^^^^^^^^
 
-SyntaxError: Unexpected reserved word
+SyntaxError: Malformed arrow function parameter list
     at Loader.moduleStrategy (internal/modules/esm/translators.js:*:*)
     at async link (internal/modules/esm/module_job.js:*:*)
diff --git a/test/parallel/test-cli-node-options.js b/test/parallel/test-cli-node-options.js
@@ -79,7 +79,7 @@ if (!['arm', 'arm64'].includes(process.arch))
   expect('--interpreted-frames-native-stack', 'B\n');
 
 // Workers can't eval as ES Modules. https://github.com/nodejs/node/issues/30682
-expectNoWorker('--experimental-top-level-await --input-type=module',
+expectNoWorker('--input-type=module',
                'B\n', 'console.log(await "B")');
 
 function expectNoWorker(opt, want, command, wantsError) {

diff --git a/test/parallel/test-no-harmony-top-level-await.mjs b/test/parallel/test-no-harmony-top-level-await.mjs
@@ -0,0 +1,11 @@
+// Flags: --no-harmony-top-level-await
+
+import {
+  mustCall,
+  disableCrashOnUnhandledRejection
+} from '../common/index.mjs';
+
+disableCrashOnUnhandledRejection();
+
+process.on('unhandledRejection', mustCall());
+Promise.reject(new Error('should not be fatal error'));
diff --git a/tools/code_cache/mkcodecache.cc b/tools/code_cache/mkcodecache.cc
@@ -27,6 +27,7 @@ int main(int argc, char* argv[]) {
 #endif  // _WIN32
 
   v8::V8::SetFlagsFromString("--random_seed=42");
+  v8::V8::SetFlagsFromString("--harmony-top-level-await");
 
   if (argc < 2) {
     std::cerr << "Usage: " << argv[0] << " <path/to/output.cc>\n";