Fix right precedence of Hack pipes by nicolo-ribaudo · Pull Request #13668 · babel/babel

nicolo-ribaudo · 2021-08-11T15:06:27Z

Q	A
Fixed Issues?
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

Spec: http://jschoi.org/21/es-hack-pipes/#sec-pipe-operator

babel-bot · 2021-08-11T15:09:36Z

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jridgewell · 2021-08-11T16:03:59Z

Was this intentional, or just an oversight? I think every other operator is left associative (with the exception of **), which would make this a weird divergence.

js-choi · 2021-08-11T16:20:48Z

@jridgewell: Yeah, Hack pipes should be right-associative, not left-associative.

Currently, Hack pipes are functionally bidirectionally associative, so (x |> (f(%) |> g(%)) always evaluates to the same thing as ((x |> f(%)) |> g(%). However, Hack pipes are more similar to => than to other operators: both |> and => create a binding over their right-hand body, and => (and by analogy |>) are therefore right-associative to support nested binding contexts.

In fact, after taking with @nicolo-ribaudo, I plan to loosen the precedence of Hack pipes in the specification to AssignmentExpression, to match => further.

Of course, for % bindings this does not matter, since a % binding is shadowed by each inner nested % binding. So currently Hack pipes are functionally bidirectionally associative. However, future extensions to Hack pipes might support binding the topic to a named identifier, à la Haskell’s do syntax, which would make right-associativity essential.

nicolo-ribaudo · 2021-08-13T20:46:46Z

Let's keep this PR only for the associativity, to give some time for the discussion at tc39/proposal-hack-pipes#11.

js-choi · 2021-08-17T15:58:40Z

This pull request could probably now be updated to the new changes as per tc39/proposal-hack-pipes#11 and tc39/proposal-hack-pipes#12:

The left-hand side is now ShortCircuitExpression.
The right-hand side is still AssignmentExpression, but the right-hand side must not cover an unparenthesized operation with the same precedence (ArrowFunction, AsyncArrowFunction, YieldExpression, ConditionalExpression, or an assignment operation). This check probably should be added to checkHackPipeBodyEarlyErrors.
The PipeBodyIsTighter error should be removed if it would not break backwards compatibility.

nicolo-ribaudo · 2021-09-04T14:03:23Z

Updated to reflect the precedence currently defined in the proposal.

js-choi · 2021-09-04T14:04:15Z

Thanks for continuing to work on this, @nicolo-ribaudo. Once we merge these in, I can work on support for ^ as the topic token.

JLHwung · 2021-09-08T14:37:58Z

+
+    const body = this.parseMaybeAssign();
+
+    const invalidBodies = {


Consider hoist this object to top level so it doesn't have to be re-created in parseHackPipeBody().

JLHwung · 2021-09-08T14:43:14Z

+      ArrowFunctionExpression: "arrow function",
+      AssignmentExpression: "assignment",
+      ConditionalExpression: "conditional",
+      YieldExpression: "yield",


Could leave a todo item here that invalidBodies currently does not handle TS extensions such as TSAsExpression, they will be supported after TypeScript supports hack pipes.

I added a todo, but I don't think that it will be a problem because:

a = b as c is an AssignmentExpression

a => b as c is an ArrowFunctionExpression

a ? b : c as d is a ConditionalExpression

yield as a is a syntax error

Oh I was meant to the plain as expression a as c. The precedence of as and |> are unclear before TS supports pipes.

JLHwung · 2021-09-08T14:45:27Z

+      YieldExpression: "yield",
+    };
+
+    if (hasOwn(invalidBodies, body.type) && !body.extra?.parenthesized) {


We can transform invalidBodies to a map so it comes with .has(), and it's also faster than objects.

nicolo-ribaudo added PR: Bug Fix 🐛 A type of pull request used for our changelog categories Spec: Pipeline Operator pkg: parser labels Aug 11, 2021

nicolo-ribaudo requested a review from js-choi August 11, 2021 15:19

jridgewell approved these changes Aug 12, 2021

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jridgewell mentioned this pull request Aug 13, 2021

Left precedence of pipeline tc39/proposal-hack-pipes#12

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nicolo-ribaudo added 3 commits September 4, 2021 15:27

Hack pipes are right-associative

ad3fc0a

[hack pipes] Loosen right precedence of |>

083e4b6

Update operator precedence

9310eec

nicolo-ribaudo force-pushed the hack-pipe-precedence branch from 467cac3 to 9310eec Compare September 4, 2021 14:01

nicolo-ribaudo commented Sep 4, 2021

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Comment thread packages/babel-parser/src/parser/expression.js Outdated

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js-choi approved these changes Sep 4, 2021

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nicolo-ribaudo added PR: Bug Fix 🐛 A type of pull request used for our changelog categories PR: Spec Compliance 👓 A type of pull request used for our changelog categories and removed PR: Bug Fix 🐛 A type of pull request used for our changelog categories labels Sep 8, 2021

nicolo-ribaudo changed the title ~~Hack pipes are right-associative~~ Fix right precedence of Hack pipes Sep 8, 2021

nicolo-ribaudo requested a review from JLHwung September 8, 2021 14:29

JLHwung approved these changes Sep 8, 2021

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JLHwung approved these changes Sep 8, 2021

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nicolo-ribaudo merged commit 3c3f520 into babel:main Sep 8, 2021

nicolo-ribaudo deleted the hack-pipe-precedence branch September 8, 2021 15:38

sosukesuzuki mentioned this pull request Sep 20, 2021

Support right precedence hack-style pipeline prettier/prettier#11557

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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 Dec 9, 2021

github-actions Bot locked as resolved and limited conversation to collaborators Dec 9, 2021


		const body = this.parseMaybeAssign();

		const invalidBodies = {

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