Private Static Fields Features: Stage 3 by rricard · Pull Request #8205 · babel/babel

rricard · 2018-06-20T19:45:32Z

Q	A
Fixed Issues?	#8052 (except accessors)
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?	Add private static fields support
Tests Added + Pass?	Tests Updated
Documentation PR
Any Dependency Changes?
License	MIT
Sponsor	@bloomberg

No changes in parser
Added a new helper to check private static field access provenance: classStaticPrivateFieldBase

While visiting a class:

Check for duplicate private static declarations

For every private static declaration add it to a container object in the classe's scope and remove it from the class itself

class C {
  static #foo = "bar";
  /*...*/
}
// will become (in loose mode):
class C {
  /*...*/
}
var _CStatics = {};
_CStatics._foo = "bar";

For every private static declaration, start visiting the class to explore each member method in order to wrap the access in the helper:

myMethod() {
  C.#foo = this.#foo + "baz";
}
// Becomes
myMethod() {
  babelHelper.classStaticPrivateFieldBase(C, C, _CStatics)._foo = 
    babelHelper.classStaticPrivateFieldBase(this, C, _CStatics)._foo + "baz";
}

babel-bot · 2018-06-21T19:46:46Z

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/8935/

rricard · 2018-06-22T21:08:44Z

We only handled private static fields for now, @tim-mc is going to help bring private static methods now. From there we'll be able to think about accessors...

rricard · 2018-06-26T14:49:53Z

It feels like this PR is ready for review.

I also would like some help for making that Travis build pass...

hzoo · 2018-06-27T21:07:52Z

.../babel-plugin-proposal-class-properties/test/fixtures/private-loose/static-undefined/exec.js

+
+expect("bar" in Foo).toBe(false)
+expect(Foo.test()).toBe(undefined)
+expect(Foo.test()).toBe(undefined)


Some of these duplicated tests are weird to me expect(Foo.test()).toBe(undefined) - I know they were just copied over but is it supposed to be testing the static and instance methods or just remove it?

Maybe it should be expect(() => Foo.test()).not.toThrow()?

@hzoo, you're right, I'll go ahead and do a second review pass on those tests (was only checking for the output I was seeing). I'm also trying to run test-262 right now against it (having npm link issues) and I might add some relevant tests then

Yeah a general thing we should do moving forward is run against test262, I know @leobalter/@rwaldron have done some work there. (@xtuc had https://github.com/xtuc/babel-test262 but we haven't used)

jridgewell · 2018-07-03T03:13:47Z

packages/babel-helpers/src/helpers.js

+
+helpers.classStaticPrivateFieldBase = () => template.program.ast`
+  export default function _classStaticPrivateFieldBase(receiver, classConstructor, privateClass) {
+    if (receiver !== classConstructor && receiver.constructor !== classConstructor) {


The receiver.constructor !== classConstructor shouldn't be necessary.

Unfortunately, this seems necessary to be spec compliant. We should discuss that on slack.

jridgewell · 2018-07-03T03:18:45Z

packages/babel-plugin-proposal-class-properties/src/index.js

-              throw path.buildCodeFrameError(
-                "Static class fields are not spec'ed yet.",
-              );
+              if (privateStaticNames.has(name)) {


Private names are shared between instance and static, ie, the following is an error:

class Example { static #x; #x; }

Wasn't sure about this one, I'll make the change.

jridgewell · 2018-07-03T03:23:41Z

.../babel-plugin-proposal-class-properties/test/fixtures/private-loose/native-classes/output.js

+var Foo =
+/*#__PURE__*/
+function () {
+  "use strict";


This is my mistake. This test case was meant to output class expressions, not compile classes to functions.

That makes more sense indeed, I'll redo the whole test dir with that then!

@jridgewell what should I do to convert tests to output class expressions?

jridgewell · 2018-07-03T03:29:47Z

packages/babel-plugin-proposal-class-properties/src/index.js

  };

+  // Traverses the class scope, handling private static name references.
+  const staticPrivatePropertyVisitor = {


We should be able to reuse privateNameVisitor. This is necessary because we have to use its inner traverser, too.

Ok, I kept them separate to make sure I don't mess with your logic but indeed, it's better to change just a few things in your logic than to branch out an entirely new one!

jridgewell · 2018-07-03T03:37:48Z

packages/babel-helpers/src/helpers.js

 `;
+
+helpers.classStaticPrivateFieldBase = () => template.program.ast`
+  export default function _classStaticPrivateFieldBase(receiver, classConstructor, privateClass) {


So there are a few issues here, and we can choose either of two ways to handle it:

We can remove this privateClass holder object for loose mode.

We can handle get, set, and call for both loose and spec mode.

The first option would allow us to reuse the same code we already have for instance private fields.

If we continue to use a holder object, we have to handle get, set, and call operations on the holder, and use the receiver as the calling context for all those cases. This complicates the runtime for loose mode. But, we're gonna need to do that anyways for spec mode.

This is super helpful, I had a hard time understanding the line between loose and spec.

jridgewell · 2018-07-03T03:39:22Z

packages/babel-plugin-proposal-class-properties/src/index.js

  };

+  const staticPrivatePropertyHandler = {
+    handle(member) {


So this doesn't handle get, set, and call operations. Given that all this is stored on a holder object, anything like ClassName.#x() will really have to be transformed to base(ClassName, ClassName, holder)['x'].call(ClassName). This currently just outputs base(ClassName, ClassName, holder)['x']().

I think I just missed something about how the handlers are working and that made it way clearer. Thanks!

rricard · 2018-07-09T14:53:47Z

Thanks @jridgewell, I'm sorry I have a lot of work on the side of this but I'll try to get back to it this week.

rricard · 2018-07-10T23:38:37Z

Todo:

get/set/call handler
Rework the helper(s)
Redo the tests

rricard · 2018-08-08T23:46:01Z

Hi @jridgewell, I could use some help changing the tests to not transform the classes. Otherwise, I think I'm almost done.

jridgewell

Sorry for being flakey. This is looking good!

jridgewell · 2018-08-18T05:25:48Z

packages/babel-helpers/src/helpers.js

+
+helpers.classStaticPrivateFieldLooseBase = () => template.program.ast`
+  export default function _classStaticPrivateFieldLooseBase(receiver, classConstructor) {
+    if (receiver !== classConstructor && receiver.constructor !== classConstructor) {


What's the receiver.constructor !== classConstructor for?

That's for when the static field gets called from this. In that case I'll probably have an instance of the class instead of the constructor itself. I do think that's what we expect from the spec but it's been a while since the last time I dived in the proposal.

It has to throw a type error if it's called on an instance of the class. This check should just be the receiver !== classConstructor.

I'm not sure, I think that if the instance is of the class type, access should work through this. I can check that again. However, in the meantime, we can restrict the access so it does not work on the instance while we figure that out.

jridgewell · 2018-08-18T05:28:06Z

packages/babel-plugin-proposal-class-properties/src/index.js

+      // Create a private static "host" object if it does not exist
+      privateClassId = path.scope.generateUidIdentifier(ref.name + "Statics");
+      staticNodesToAdd.push(
+        template.statement`const PRIVATE_CLASS_ID = {};`({


Nit: Should probably use a prototype-less object here.

jridgewell · 2018-08-18T05:28:55Z

packages/babel-plugin-proposal-class-properties/src/index.js

-            }
            if (privateNames.has(name)) {
-              throw path.buildCodeFrameError("Duplicate private field");
+              throw path.buildCodeFrameError("Duplicate static private field");


Let's leave this as the old message.

jridgewell · 2018-08-18T05:29:56Z

packages/babel-plugin-proposal-class-properties/src/index.js

+                state,
+                privateClassId,
+              );
+              staticNodesToAdd.forEach(node => staticNodes.push(node));


Can just staticNodes.push(...staticNodesToAdd)

rricard · 2018-08-20T10:52:48Z

@jridgewell don't worry, we're in no rush. I'll just need some help setting up the tests correctly.

rricard · 2018-08-20T21:45:11Z

I was trying to prevent the class transform itself but I managed to get that right in the plane

rricard · 2018-08-20T21:45:34Z

It should be good for a second review

jridgewell

Looking good!

Need tests for loose, and some that do a call operation on the private static.

jridgewell · 2018-08-20T22:10:58Z

packages/babel-plugin-proposal-class-properties/src/index.js

+    const { scope, parentPath } = path;
+    const { key, value } = path.node;
+    const { name } = key.id;
+    const privateId = scope.generateUidIdentifier(name);


Nit: So we actually don't need to generate a unique id here, we can just use name.

rricard · 2018-08-20T23:10:48Z

Loose tests have been removed while I changed my test methodology, they're back now. I also removed the privateId for spec mode but not loose mode (where the unique id prevents test breakage in loose mode)

rricard · 2018-08-20T23:44:24Z

Rebased the whole thing. Still need to test call operation

rricard · 2018-08-24T21:36:26Z

@jridgewell I think this covers all of the requested changes. Thanks!

jridgewell · 2018-08-26T04:07:30Z

.../babel-plugin-proposal-class-properties/test/fixtures/private-loose/native-classes/output.js

+
+}
+
+Foo._foo = "foo";


My last nit: This should be using Object.defineProperty with { enumerable: false, configurable: false }. We can do this in a follow PR if you'd like.

That is a good point, I'll try to put that here before we merge

rricard · 2018-08-26T19:01:20Z

@jridgewell I made the change, would you like to have it in a separate helper though?

jridgewell

This is all good. Need one more approval before we can merge.

jridgewell · 2018-09-01T04:42:15Z

Eh, let's just go for it.

nicolo-ribaudo · 2018-09-03T09:37:30Z

I'm sorry, I forgot to review this PR 😅
I'll open a few PR with some small tweaks.

rricard mentioned this pull request Jun 20, 2018

Static Class Features: Stage 3 #8052

Closed

rricard force-pushed the static-class-feature-stage-3 branch 4 times, most recently from 2824e86 to 1c43798 Compare June 21, 2018 19:46

rricard force-pushed the static-class-feature-stage-3 branch from 1c43798 to b00fa81 Compare June 21, 2018 19:47

rricard changed the title ~~[WIP] Static Class Features: Stage 3~~ Private Static Fields: Stage 3 Jun 22, 2018

rricard changed the title ~~Private Static Fields: Stage 3~~ [wip] Private Static Features: Stage 3 Jun 22, 2018

rricard mentioned this pull request Jun 25, 2018

Private Methods (and accessors) (Stage 3) babel/proposals#22

Open

rricard force-pushed the static-class-feature-stage-3 branch from 181e814 to ff1203e Compare June 26, 2018 13:56

rricard changed the title ~~[wip] Private Static Features: Stage 3~~ Private Static Fields Features: Stage 3 Jun 26, 2018

rricard force-pushed the static-class-feature-stage-3 branch from ff1203e to 69e5e2e Compare June 26, 2018 14:19

hzoo requested a review from jridgewell June 27, 2018 20:59

hzoo reviewed Jun 27, 2018

View reviewed changes

hzoo requested a review from nicolo-ribaudo June 27, 2018 21:08

hzoo added Spec: Class Fields PR: New Feature 🚀 A type of pull request used for our changelog categories labels Jun 27, 2018

jridgewell requested changes Jul 3, 2018

View reviewed changes

rricard force-pushed the static-class-feature-stage-3 branch 2 times, most recently from e9c8e56 to 83fbdbc Compare July 10, 2018 14:27

rricard force-pushed the static-class-feature-stage-3 branch 2 times, most recently from 2923f1b to 1c448ee Compare July 20, 2018 21:42

jridgewell reviewed Aug 18, 2018

View reviewed changes

rricard force-pushed the static-class-feature-stage-3 branch from e061a59 to 93e205a Compare August 20, 2018 21:43

jridgewell reviewed Aug 20, 2018

View reviewed changes

Robin Ricard added 2 commits August 20, 2018 16:42

Private Static Class Fields Implementation

7c38dfd

Redo testing without class transform for static private

6dc2a28

rricard force-pushed the static-class-feature-stage-3 branch from eb66be9 to 6dc2a28 Compare August 20, 2018 23:44

Add a call() test for private static

deefb8c

jridgewell approved these changes Aug 26, 2018

View reviewed changes

Use Object.defineProperty in loose mode

5623c2d

jridgewell approved these changes Aug 28, 2018

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jridgewell merged commit fb66fa6 into babel:master Sep 1, 2018

This was referenced Sep 3, 2018

[static private] Use correct min version in helpers #8613

Merged

[static private] Unify loose handling of static and instance props #8614

Merged

Merge class features plugins #8130

Merged

ghost mentioned this pull request Oct 1, 2018

Update @babel/preset-env in /modules/frontend from 7.0.0-beta.42 to 7.1.0 project-accelerate/accelerate#248

Open

tim-mc mentioned this pull request Jan 28, 2019

Private Static Methods (Stage 3) babel/proposals#55

Closed

tim-mc mentioned this pull request Mar 13, 2019

Private Static Accessors (Stage 3) babel/proposals#56

Open

lock bot added the outdated A closed issue/PR that is archived due to age. Recommended to make a new issue label Oct 4, 2019

lock bot locked as resolved and limited conversation to collaborators Oct 4, 2019


		}

		Foo._foo = "foo";

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