Parse `using` declaration (explicit resource management) #14968

JLHwung · 2022-09-22T20:39:39Z

Q	A
Fixed Issues?	Implement parsing/printing support of the stage-2 Explicit Resource Management proposal
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?	Yes
Tests Added + Pass?	Yes
Documentation PR Link	babel/website#2684
Any Dependency Changes?
License	MIT

This PR parses / generates the using declaration

{
  using handler = getHandler()
}

introduced by the Explicit Resource Management proposal. We also create the new syntax plugin and add it to the babel-standalone.

I suggest reviewing this PR by commits.

/cc @rbuckton

babel-bot · 2022-09-22T20:43:25Z

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/53239/

JLHwung · 2022-09-22T20:49:06Z

packages/babel-parser/src/parser/statement.ts

+        lookaheadAhead.type === tt._of &&
+        lookaheadAhead.end - lookaheadAhead.start === 2
+      ) {
+        // using of of ...


In the worst scenario, we have to do triple lookahead to differentiate between using of of of and using of of.

@rbuckton Maybe we can forbid of as a using binding in for-of? So for (using of must be a for-LHS and we don't have to peek more.

Isn't it the same as let of of of? Or is of disallowed in that case?

for ( [lookahead ∉ { let, async of }] LeftHandSideExpression[?Yield, ?Await] of AssignmentExpression[+In, ?Yield, ?Await] ) Statement[?Yield, ?Await, ?Return]

for-of has disabled let and async as LHS so for(let of of must start a for-of with a let-binding of. But using comes after for-of so we have to recognize for(using of of) as for-of with using as LHS.

Per tc39/proposal-explicit-resource-management#107, I will disallow of as a for-using-of binding name, hopefully we will get rid of extra lookahead, too.

There is now a PR that addresses this in the proposal repository.

packages/babel-parser/src/parser/statement.ts

nicolo-ribaudo · 2022-10-04T16:53:34Z

packages/babel-generator/src/generators/statements.ts

+    // Ensure no line break between `using` and the first declarator
+    iterator = (_, i: number) => {
+      if (i === 0) {
+        this._noLineTerminator = _noLineTerminator;


Shouldn't we also unset _noLineTerminator after printing?

Do you mean unset _noLineTerminator after printing the using keyword? The variable _noLineTerminator here stores the value of this.noLineTerminator before we print using, and then we restore this._noLineTerminator after the first declarator is printed.

packages/babel-parser/src/parser/statement.ts

liuxingbaoyu · 2022-10-15T01:56:37Z

packages/babel-generator/test/fixtures/using-declarations/basic/output.js

 {
  using /* 1 */a = foo(),
-
-  /* 2 */
-  b = foo();
+    /* 2 */b = foo();
 }


The comments and indentation look fine.😃

liuxingbaoyu

Just a small question: I noticed that the newly added containsEsc property is only doing reads and no writes, is this expected?

JLHwung · 2022-10-15T14:21:05Z

Just a small question: I noticed that the newly added containsEsc property is only doing reads and no writes, is this expected?

The containsEsc will be set by the tokenizer by readWord

babel/packages/babel-parser/src/tokenizer/index.ts

Line 1380 in 0b0f083

this.state.containsEsc = false;

So if we see an identifier, lookahead.containsEsc will be a boolean, otherwise lookahead will not have a containsEsc property.

JLHwung added PR: New Feature 🚀 A type of pull request used for our changelog categories Spec: Explicit Resource Management labels Sep 22, 2022

JLHwung commented Sep 22, 2022

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JLHwung commented Sep 23, 2022

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packages/babel-parser/src/parser/statement.ts Outdated Show resolved Hide resolved

JLHwung force-pushed the parse-using-declaration branch from 99e5f75 to 6cd106e Compare September 27, 2022 19:16

liuxingbaoyu added this to the 7.20.0 milestone Sep 28, 2022

nicolo-ribaudo reviewed Oct 4, 2022

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nicolo-ribaudo approved these changes Oct 4, 2022

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packages/babel-parser/src/parser/statement.ts Outdated Show resolved Hide resolved

nicolo-ribaudo added the PR: Needs Docs label Oct 4, 2022

rbuckton mentioned this pull request Oct 4, 2022

Disallow 'for (using of of ...)' tc39/proposal-explicit-resource-management#108

Merged

JLHwung force-pushed the parse-using-declaration branch from 3b45a7b to f9e12dd Compare October 14, 2022 20:30

liuxingbaoyu reviewed Oct 15, 2022

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liuxingbaoyu approved these changes Oct 15, 2022

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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 Oct 16, 2022

JLHwung added 13 commits October 25, 2022 10:13

Add types definitions

c5f08d1

refactor: move inline isLet check

7b04607

parse using declarations

0d872c1

generate using declarations

2a23635

register using declaration as const binding

8fd8dba

update AST spec

f423058

respect using declaration kind

212ce2b

add syntax plugin

0ff93a1

add syntax plugin to standalone

e5b1362

disallow of as a for-using-of binding

09f2552

update generator test case

3d7e2fe

update test fixtures

d01203b

address review comments

4a50d5e

JLHwung force-pushed the parse-using-declaration branch from 4f0e6ff to 4a50d5e Compare October 25, 2022 14:14

JLHwung removed the PR: Needs Docs label Oct 25, 2022

update test fixtures

f3b781a

nicolo-ribaudo changed the title ~~Parse using declaration~~ Parse using declaration (explicit resource management) Oct 26, 2022

nicolo-ribaudo merged commit 8300960 into babel:main Oct 26, 2022

nicolo-ribaudo deleted the parse-using-declaration branch October 26, 2022 19:36

This was referenced Oct 29, 2022

Add raw to Identifier? estree/estree#291

Open

Add .raw or .extra.raw to Identifier #15117

Open

shaneomatz mentioned this pull request Nov 18, 2022

[Snyk] Upgrade @babel/runtime from 7.12.5 to 7.20.0 shaneomatz/video.js#1

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This was referenced Nov 24, 2022

[Bug]: Babel throws on computed property access using[x] #15221

Closed

Parse using[foo] as computed member expression #15225

Merged

github-actions bot added the outdated A closed issue/PR that is archived due to age. Recommended to make a new issue label Jan 26, 2023

github-actions bot locked as resolved and limited conversation to collaborators Jan 26, 2023

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Parse using declaration (explicit resource management) #14968

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Parse `using` declaration (explicit resource management) #14968

Parse `using` declaration (explicit resource management) #14968

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