Private Class Methods Stage 3: Private Accessors #9101

tim-mc · 2018-11-29T19:25:25Z

Q	A
Fixed Issues?	babel/proposals#22
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?	Add private accessors support
Tests Added + Pass?	Yes
Documentation PR
Any Dependency Changes?	No
License	MIT
Sponsor	@bloomberg

This is a follow-up to #8654. It adds support for private accessors within the current babel-plugin-class-features + babel-plugin-proposal-private-methods plugin combination.

cc: @robpalme @littledan @syg @jridgewell @nicolo-ribaudo

babel-bot · 2018-11-29T19:30:22Z

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/9811/

tim-mc · 2018-11-29T19:43:16Z

I'd like to get some feedback on how this should be handling the usage of update expressions and certain assignment expressions. I'm not sure what exactly the expectation is for how to handle these situations:

// update expressions
this.#privateSetter++;
this.#privateSetter--;
++this.#privateSetter;
// etc.

// assignment expressions
this.#privateSetter += 'foo';
this.#privateSetter -= 'foo';

I made a method that checks for these scenarios which is used in both the spec and loose private name handlers.

My main question is: should these usages be throwing errors? If so,

Should they be code frame errors?
Is this the proper place to throw an error? I considered putting it over here in features.js, but since this isn't really a check for a "feature," that seemed wrong.

If they should not be throwing, what would be the proper way to handle these?

...babel-plugin-proposal-private-methods/test/fixtures/private-method-loose/accessors/output.js

nicolo-ribaudo · 2018-11-29T23:04:50Z

Can't ++this.#privateSetter; be desugared to this.#privateSetter = this.#privateSetter + 1, which should set it to NaN?

++this.#privateGetter; should instead throw at runtime, since it is trying to set a non-writable property.

Btw, I think that these cases are easier if you rely on the existing fields descriptor handling logic.

tim-mc · 2018-12-24T19:34:20Z

@nicolo-ribaudo I've made the updates to the PR that we discussed.

packages/babel-helper-create-class-features-plugin/src/index.js

nicolo-ribaudo · 2018-12-27T23:00:04Z

packages/babel-helpers/src/helpers.js

+      }
+
+      descriptor.value = value;
+      return value;


return value; should be outside the if/else, because we always need to return it.

nicolo-ribaudo · 2018-12-27T23:02:06Z

packages/babel-helper-create-class-features-plugin/src/fields.js

+            methodId:
+              isMethod && isInstance && prop.node.kind === "method"
+                ? prop.scope.generateUidIdentifier(name)
+                : undefined,


Nit: could you move the methodId definition inside an if condition, like you did for getId and setId?

nicolo-ribaudo · 2018-12-27T23:04:13Z

packages/babel-helper-create-class-features-plugin/src/fields.js

@@ -404,7 +535,7 @@ export function buildFieldsInitNodes(

  return {
    staticNodes,
-    instanceNodes,
+    instanceNodes: instanceNodes.filter(instanceNode => instanceNode),


Nit: we usually use .filter(Boolean)

packages/babel-helper-create-class-features-plugin/src/index.js

nicolo-ribaudo · 2018-12-27T23:07:04Z

This PR looks almost ready!

tim-mc · 2018-12-27T23:16:46Z

@nicolo-ribaudo requested changes have been made.

nicolo-ribaudo · 2018-12-27T23:30:07Z

Can you add a test for the helper change? Something like

let foo;
class Cl {
  set #foo(v) { return 1 }
  test() {
    foo = this.#foo = 2;
  }
}

new Cl().test();

expect(foo).toBe(2);

Also, it would be good to have the following tests:

duplicated-names/get-set // does not throw
duplicated-names/set-get // does not throw
duplicated-names/get-get // throws at compile time
duplicated-names/set-set // throws at compile time
duplicated-names/get-method // throws at compile time
duplicated-names/method-get // throws at compile time
duplicated-names/set-method // throws at compile time
duplicated-names/method-set // throws at compile time
duplicated-names/method-method // throws at compile time. Not really related to this PR, but since we are adding all the other tests it would be good.
accessors/set-only-getter // throws at runtime (e.g. get #foo() {} ... this.#foo = 2)
accessors/get-only-setter // returns undefined
accessors-loose/set-only-getter // throws at runtime
accessors-loose/get-only-setter // returns undefined
Move the testUpdates functions to accessors/updates and accessors-loose/updates
Move the remaining code from private-methods/accessors and private-methods-loose/accessors to accessors/basic and accessors-loose/basic

tim-mc · 2018-12-28T15:41:58Z

@nicolo-ribaudo Ok, updated with new & modified tests.

nicolo-ribaudo · 2019-01-06T20:05:23Z

packages/babel-plugin-proposal-private-methods/test/fixtures/accessors-loose/options.json

+    [
+      "external-helpers",
+      {
+        "helperVersion": "7.1.6"


Could you use something like 7.1000.0? So that we don't have to change this file if the helpers change in a futue version.

Sure, done.

nicolo-ribaudo

🎉

littledan · 2019-01-07T23:26:11Z

🎉 🎉

hzoo · 2019-01-16T17:38:29Z

packages/babel-plugin-proposal-private-methods/test/fixtures/accessors-loose/options.json

+    ["proposal-class-properties", { "loose": true }],
+    "transform-classes",
+    "transform-block-scoping",
+    "syntax-class-properties"


Not specific to this test/PR but was wondering if we actually need to include these plugins?

"transform-block-scoping", "syntax-class-properties"

xtuc · 2019-01-17T16:23:22Z

packages/babel-helper-create-class-features-plugin/src/fields.js

+    const isPrivate = prop.isPrivate();
+    const isMethod = !prop.isProperty();
+    const isInstance = !prop.node.static;
+    if (isPrivate) {


isPrivate seems only used here? Could you please inline it?

xtuc · 2019-01-17T16:25:08Z

packages/babel-helper-create-class-features-plugin/src/fields.js

+        initNodes.push(template.statement.ast`var ${id} = new WeakMap();`);
+      } else {
+        initNodes.push(template.statement.ast`var ${id} = new WeakSet();`);
+      }


The only difference is WeakMap vs WeakSet. Could we switch to an AST here and just parametrize that?

xtuc · 2019-01-17T16:25:19Z

packages/babel-helper-create-class-features-plugin/src/fields.js

+        initNodes.push(template.statement.ast`var ${id} = new WeakMap();`);
+      } else {
+        initNodes.push(template.statement.ast`var ${id} = new WeakSet();`);
+      }
    } else if (!isStatic) {
      initNodes.push(template.statement.ast`var ${id} = new WeakMap();`);


See comment above

xtuc · 2019-01-17T16:26:45Z

packages/babel-helper-create-class-features-plugin/src/fields.js

+        });
+      `;
+    }
+  }


This looks quite verbose to me, could we switch it to building an AST and parametrizing the set/get? Also, I believe we have a few helpers that we could use here.

hzoo · 2019-01-21T23:30:02Z

Released in 7.3! Thanks everyone https://twitter.com/NicoloRibaudo/status/1087473662696017922?s=20

tim-mc force-pushed the private-class-methods-stage-3_accessors branch from 1af57eb to d9593cb Compare November 29, 2018 19:25

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Update progress of Babel Implementation tc39/proposal-private-methods#53

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Add support for decorators with private elements - Spec mode #9154

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Babel 7.3.0 #9334

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tim-mc added 11 commits January 17, 2019 09:36

Add accessor loose support

af5db96

Add private accessors spec support

621828a

Fix private dupe name check

9e41394

Changes from code review

5fcbd17

Add duplicated names tests

83c135c

Add get/set-only tests

a5d2172

Move accessors tests

f0d6486

Split out updates tests

2498ec2

Add helper change tests

4a328b1

Update test output

d6ccba0

Update test options

62a0ca4

tim-mc force-pushed the private-class-methods-stage-3_accessors branch from e1b2bcb to 62a0ca4 Compare January 17, 2019 15:05

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nicolo-ribaudo merged commit e8de6fa into babel:master Jan 21, 2019

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This was referenced Jan 22, 2019

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

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

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tim-mc mentioned this pull request Mar 13, 2019

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

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Private Class Methods Stage 3: Private Accessors #9101

Private Class Methods Stage 3: Private Accessors #9101

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hzoo commented Jan 21, 2019

Private Class Methods Stage 3: Private Accessors #9101

Private Class Methods Stage 3: Private Accessors #9101

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