Enable top-level `await` parsing by default #13387

nicolo-ribaudo · 2021-05-28T16:26:48Z

Q	A
Fixed Issues?	Ref: babel/proposals#74 (comment)
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?	Yes
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

nicolo-ribaudo · 2021-05-28T16:27:26Z

packages/babel-parser/test/fixtures/es2015/uncategorised/357/options.json

@@ -1,3 +1,4 @@
 {
-  "sourceType": "module"
+  "sourceType": "module",
+  "throws": "Unexpected token (1:6)"


The input code is await = foo();. We can potentially recover here I think, parsing await as an identifier.

nicolo-ribaudo · 2021-05-28T16:29:07Z

packages/babel-parser/test/fixtures/es2015/uncategorised/359/output.json

@@ -2,7 +2,7 @@
  "type": "File",
  "start":0,"end":20,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":20}},
  "errors": [
-    "SyntaxError: Unexpected reserved word 'await'. (1:6)"
+    "SyntaxError: Can not use 'await' as identifier inside an async function. (1:6)"


The input code is const await = foo();. As reported on twitter by @KFlash, this error message is confusing (https://twitter.com/buzyescayadev/status/1398240006670454784).

I will open a follow-up PR to fix it, to keep this one as only switching the plugin on by default.

We could just change the error message to "... async function or top level module".

@JLHwung then what will be the error message when you are parsing in an non-async func body or arrow? Same error?
None of this is consistent with the error message thrown when e.g. parsing out a formal param list with await.

await = x is an unexpected token? Where is that token? Between 1 - 6 there are 3x token and 2x whitespace

function x () { await } trigger an different error message again.

The token is the one at line 1, column 6: any editor, or the Babel cli, or Babel integrations will point to the =.

Maybe we can always throw Unexpected reserved word 'await'. in modules (since the reason we throw is that it's reserved), and keep throwing the current error in async functions inside scripts (await is not reserved there, but it's special-cased to be illegal).

babel-bot · 2021-05-28T16:29:25Z

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codesandbox-ci · 2021-05-28T16:30:43Z

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JLHwung · 2021-05-28T18:17:12Z

scripts/parser-tests/typescript/allowlist.txt

@@ -221,6 +222,7 @@ exportSpecifierAndLocalMemberDeclaration.ts
 exportStarFromEmptyModule.ts
 exportStarNotElided.ts
 expressionsForbiddenInParameterInitializers.ts
+extendedUnicodePlaneIdentifiers.ts


I have no idea why this test is in allowlist:

Source

Babel parser parses successfully, as expected. (repl)

JLHwung · 2021-05-28T18:25:42Z

scripts/parser-tests/flow/allowlist.txt

 decorators/migrated_0003.js
 export_import_reserved_words/migrated_0003.js
 export_statements/export_trailing_comma.js
+for_await_loops/migrated_0000.js


For reference, this file now parses successfully due to top level await,

for await (let x of e) {}

and we assume all the Flow parser tests are running with module source type.

JLHwung · 2021-05-28T18:27:56Z

scripts/parser-tests/flow/allowlist.txt

@@ -5,6 +5,7 @@ JSX/invalid_unpaired_rcurly.js
 JSX_invalid/migrated_0000.js
 arrow_function/object_return_type.js
 arrow_function_invalid/migrated_0002.js
+async_arrow_functions/with_type_parameters_types_disabled.js


This test is added because Flow has a new test options: types: boolean that can control whether parameter types should be parsed:

https://github.com/facebook/flow/blob/master/src/parser/test/flow/async_arrow_functions/with_type_parameters_types_disabled.options.json

We don't have such an option.

From a parsing perspective, is it the same as all: true?

JLHwung · 2021-05-28T18:31:01Z

scripts/parser-tests/flow/allowlist.txt

+comment_interning/class_method.js
+comment_interning/class_property.js
+comment_interning/declare_export_declaration.js
+comment_interning/declare_interface.js
+comment_interning/declare_type_alias.js
+comment_interning/decorator.js
+comment_interning/function_declaration.js
+comment_interning/import.js
+comment_interning/interface.js
+comment_interning/object_type.js
+comment_interning/remove_type_trailing_comments.js
+comment_interning/super.js
+comment_interning/type_alias.js


Babel is throwing on these cases because of duplicate class declaration class C. The Flow parser is tolerant on duplicate binding, which are throw later by the type checker.

JLHwung · 2021-07-23T13:51:32Z

packages/babel-parser/src/parser/expression.js

-          startPos,
-          this.hasPlugin("topLevelAwait")
-            ? Errors.AwaitNotInAsyncContext
-            : Errors.AwaitNotInAsyncFunction,


We can remove unused Errors.AwaitNotInAsyncFunction.

RedGuy12 · 2021-08-17T20:12:30Z

does this mean i no longer need @babel/plugin-syntax-top-level-await anymore?

nicolo-ribaudo · 2021-08-17T20:18:14Z

Correct! But you need to make sure to use @babel/parser ^7.15.0 (if you are using @babel/core@^7.15.0 it depends on a new enough version of @babel/parser).

RedGuy12 · 2021-08-17T20:48:39Z

i'm only using @babel/eslint-parser while i wait for eslint v8 to ship with top-level await support

here is the related part of my config:

	parser: "@babel/eslint-parser",
	parserOptions: {
		requireConfigFile: false,
		sourceType: "module",
		babelOptions: {
			plugins: [
				"@babel/plugin-syntax-top-level-await"
			],
		},
	}

can I just remove plugins and it will work? or do I have to do other things as well? thanks

nicolo-ribaudo · 2021-08-17T21:31:40Z

Yes, it should work.

nicolo-ribaudo added PR: New Feature 🚀 A type of pull request used for our changelog categories pkg: parser labels May 28, 2021

nicolo-ribaudo commented May 28, 2021

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nicolo-ribaudo force-pushed the tla-default branch from 330acd3 to 8dbbbae Compare May 28, 2021 16:43

nicolo-ribaudo added this to the v7.15.0 milestone May 28, 2021

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jridgewell approved these changes May 29, 2021

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nicolo-ribaudo force-pushed the tla-default branch from a4df67e to 28cd2c8 Compare July 17, 2021 19:30

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nicolo-ribaudo force-pushed the tla-default branch from 28cd2c8 to d92d4cd Compare July 22, 2021 20:17

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nicolo-ribaudo added the PR: Ready to be Merged A pull request with already two approvals, but waiting for the next minor release label Jul 26, 2021

nicolo-ribaudo force-pushed the tla-default branch from d92d4cd to cfe17ab Compare July 26, 2021 16:00

nicolo-ribaudo added 4 commits July 30, 2021 23:39

Enable top-level await by default

1231e82

Update Flow and TS tests

bfd3b11

Remove from test262 parser tests

d3641c0

Update env tests

62473e4

nicolo-ribaudo force-pushed the tla-default branch from cfe17ab to 62473e4 Compare July 30, 2021 21:39

nicolo-ribaudo merged commit ddaf0d4 into babel:main Aug 3, 2021

nicolo-ribaudo deleted the tla-default branch August 3, 2021 22:00

This was referenced Aug 5, 2021

chore(deps-dev): bump @babel/eslint-parser from 7.13.14 to 7.15.0 filecoin-project/slate#863

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chore(deps-dev): bump @babel/core from 7.13.14 to 7.15.0 filecoin-project/slate#862

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fisker mentioned this pull request Aug 8, 2021

Update babel parser sindresorhus/eslint-plugin-unicorn#1472

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github-actions bot added the outdated A closed issue/PR that is archived due to age. Recommended to make a new issue label Nov 17, 2021

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Enable top-level `await` parsing by default #13387

Enable top-level `await` parsing by default #13387

nicolo-ribaudo commented May 28, 2021 •

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RedGuy12 commented Aug 17, 2021

nicolo-ribaudo commented Aug 17, 2021

RedGuy12 commented Aug 17, 2021

nicolo-ribaudo commented Aug 17, 2021

Enable top-level await parsing by default #13387

Enable top-level await parsing by default #13387

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RedGuy12 commented Aug 17, 2021

nicolo-ribaudo commented Aug 17, 2021

RedGuy12 commented Aug 17, 2021

nicolo-ribaudo commented Aug 17, 2021

Enable top-level `await` parsing by default #13387

Enable top-level `await` parsing by default #13387

nicolo-ribaudo commented May 28, 2021 •

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