Property variance type annotations for Flow plugin #161

samwgoldman · 2016-10-07T23:56:43Z

Non-method properties and indexers of object types, declare class, and
interfaces can be "positive" or "negative." Class fields, but again not
methods, can also have variance.

This PR generalizes the variance annotations for type parameters into a
new node type, and reuses that node for those properties.

The code for object types is reused for interfaces and declare classes.
The changes there are straightfoward.

The code for class fields is reused for object literals, which do not
support variance annotations (currently). This code is a bit sketchy,
because we always parse variance annotations in the parsePropertyName
extension, then error in a the subsequent parse phase for object
literals (parseObjPropValue) or class methods (parseClassMethod).

Non-method properties and indexers of object types, declare class, and interfaces can be "positive" or "negative." Class fields, but again not methods, can also have variance. This PR generalizes the variance annotations for type parameters into a new node type, and reuses that node for those properties. The code for object types is reused for interfaces and declare classes. The changes there are straightfoward. The code for class fields is reused for object literals, which do not support variance annotations (currently). This code is a bit sketchy, because we always parse variance annotations in the `parsePropertyName` extension, then error in a the subsequent parse phase for object literals (`parseObjPropValue`) or class methods (`parseClassMethod`).

babel/babylon#161 adds parsing support for property variance annotations. This PR adds the necessary node type for the new Variance node and generate support for all the positions where variance can now appear.

samwgoldman · 2016-10-08T00:27:58Z

Tests fail due to missing babel support, which is added in the referenced PR to Babel.

Is it possible to bump these versions in lock step, or do I need to break up this change into multiple steps?

danez

Looks good, just two minor nitpicks

danez · 2016-10-08T19:16:24Z

src/plugins/flow.js

+    } else if (this.state.value === "-") {
+      variance.kind = "minus";
+    }
+    this.eat(tt.plusMin);


We could simplify that here and do this.eat(tt.plusMin) already in the if () and remove this line then.

That actually slightly changes the behavior here, because calling eat in the conditional expression advances the parser, so when I call startNode the start position is off by one.

I could also write this, but I think don't think it's clearly better:

let variance = this.startNode(); if (this.eat(tt.plusMin)) { // ... } else { variance = null; } return variance;

Will change the eat(plusMin) to next(), which will hopefully clarify the intent better. The tests do exercise the node positioning, so regression is unlikely here.

Ah I see, sorry.

danez · 2016-10-08T19:18:53Z

src/plugins/flow.js

@@ -380,6 +379,10 @@ pp.flowParseObjectType = function (allowStatic, allowExact) {
      }
      if (this.isRelational("<") || this.match(tt.parenL)) {
        // This is a method property
+        if (variance) {
+          this.unexpected(variance.start);
+          variance = null;


This doesn't makes sense as this.unexpected() throws anyway. Maybe we want to assignment after the diff, although not sure if necessary.

Good catch! These two assignments are totally bogus :P

samwgoldman · 2016-10-10T19:03:04Z

Heads up, I'm going to change this to roll back the addition of a new variance node. Instead, I will continue to use the "plus" | "minus" | null format that currently exists for type parameters.

Adding a new node type, specifically changing the TypeParameter node's variance property to be node-valued, is a breaking change. We might choose to make this breaking change in a later version.

codecov-io · 2016-10-11T00:17:42Z

Current coverage is 94.55% (diff: 97.29%)

No coverage report found for master at 2697bfd.

Powered by Codecov. Last update 2697bfd...a4c9e8f

samwgoldman · 2016-10-11T00:37:16Z

OK, I removed the new node type, so this is no longer a breaking change. In order to preserve the existing error messages, I needed to pass around the position of the variance annotation out-of-band, which is a bit hacky, because we need to be careful to clean up after ourselves with delete.

In the future, when Babel approaches a major version and we can make the breaking change, I'd like to go back to having a separate node type for variance annotations.

danez

One minor thing I'm unsure but else looks good now. After we merge this, I can create a new PR with the breaking change for the next major bump.

danez · 2016-10-12T08:40:05Z

src/plugins/flow.js

@@ -1052,9 +1055,10 @@ export default function (instance) {
  instance.extend("parseObjPropValue", function (inner) {
    return function (prop) {
      if (prop.variance) {
-        this.unexpected(prop.variance.start);
+        this.unexpected(prop.start);


Should this be prop.variancePos?

👍 Yup. In this case they are one-in-the-same, but this should definitely be variancePos for clarity. We wouldn't need variancePos except for static properties on classes, which share the same AST building code.

) * Add variance node type and generate property variance annotations babel/babylon#161 adds parsing support for property variance annotations. This PR adds the necessary node type for the new Variance node and generate support for all the positions where variance can now appear. * Variance is no longer a separate node type This diff also adds tests to class properties and to the flow-strip-types transform. * Add test + fix for edge case with variance and class proeprties

* Property variance type annotations for Flow plugin Non-method properties and indexers of object types, declare class, and interfaces can be "positive" or "negative." Class fields, but again not methods, can also have variance. This PR generalizes the variance annotations for type parameters into a new node type, and reuses that node for those properties. The code for object types is reused for interfaces and declare classes. The changes there are straightfoward. The code for class fields is reused for object literals, which do not support variance annotations (currently). This code is a bit sketchy, because we always parse variance annotations in the `parsePropertyName` extension, then error in a the subsequent parse phase for object literals (`parseObjPropValue`) or class methods (`parseClassMethod`). * Remove bogus unreachable code, clarify variance parsing conditional * Don't use a new node type for variance annotations Adding a new node type, specifically changing the TypeParameter node's variance property to be node-valued, is a breaking change. We might choose to make this breaking change in a later version. * s/start/variancePos

…bel#4697) * Add variance node type and generate property variance annotations babel/babylon#161 adds parsing support for property variance annotations. This PR adds the necessary node type for the new Variance node and generate support for all the positions where variance can now appear. * Variance is no longer a separate node type This diff also adds tests to class properties and to the flow-strip-types transform. * Add test + fix for edge case with variance and class proeprties

samwgoldman mentioned this pull request Oct 8, 2016

Add variance node type and generate property variance annotations babel/babel#4697

Merged

danez suggested changes Oct 8, 2016

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Remove bogus unreachable code, clarify variance parsing conditional

56a69fb

danez approved these changes Oct 8, 2016

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danez added area: flow spec-update labels Oct 8, 2016

Don't use a new node type for variance annotations

0651e0a

Adding a new node type, specifically changing the TypeParameter node's variance property to be node-valued, is a breaking change. We might choose to make this breaking change in a later version.

danez suggested changes Oct 12, 2016

View reviewed changes

s/start/variancePos

a4c9e8f

danez mentioned this pull request Oct 13, 2016

[7.0] Switch variance to be a separate node babel/babel#4722

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danez approved these changes Oct 14, 2016

View reviewed changes

danez merged commit 26809e8 into babel:master Oct 14, 2016

danez mentioned this pull request Sep 3, 2017

Align flow-parser with babylon v7 facebook/flow#4789

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Property variance type annotations for Flow plugin #161

Property variance type annotations for Flow plugin #161

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Property variance type annotations for Flow plugin #161

Property variance type annotations for Flow plugin #161

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Current coverage is 94.55% (diff: 97.29%)

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