1793963 - Code generation for class decorators

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P2)

Description

[Dan Minor [:dminor]]

Code generation for decorators is likely to be complicated, so we'll split it into multiple bugs. This bug covers code generation for class decorators.

Comment 1

[Alex Vincent [:WeirdAl]]

Please note: in the shims and TypeScript experimental support I've seen, the order of class decorators may be backwards, compared to other types of decorators.

Comment 2

[Alex Vincent [:WeirdAl]]

:-) TypeScript 5 nightlies seem to get the ordering of class decorators from top to bottom, rather than from bottom to top as comment 1 shows. I think TS5 has it right.

Comment 3

[Alex Vincent [:WeirdAl]]

OK, I really need to apologize, because after a year, I finally understand that decorators running from bottom to top is desirable. The reasoning has to do with the classes they return.

For class decorators which can return a new class, top-to-bottom implies the earliest decorator returns the outermost class:

class C extends B {
}

class B extends A {
}

class A {
}

This would be like:

@C
@B
class A {
}

That's why class decorators run backwards, from bottom to top.

I think the appropriate punishment for so much bug spam is to make me write the class decorators documentation on developer.mozilla.org.

Comment 4

[Dan Minor [:dminor]]

Attachment: Bug 1793963 - Add InternalWhileEmitter; r=arai

We currently synthesize a while loop to process initializers added by decorators, but this
while loop doesn't really have a location in the input source, so we fake it. This adds
a version of WhiteEmitter::Cond that does not take source coordinates to avoid
triggering assertions about the coordinate validity.

Comment 5

[Dan Minor [:dminor]]

Attachment: Bug 1793963 - Add bytecode generation for class decorators; r=arai

Depends on D184147

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/d40ced9b1d57
Add InternalWhileEmitter; r=arai
https://hg.mozilla.org/integration/autoland/rev/b91fdb9d2883
Add bytecode generation for class decorators; r=arai

Comment 7

[Noemi Erli[:noemi_erli]]

https://hg.mozilla.org/mozilla-central/rev/d40ced9b1d57
https://hg.mozilla.org/mozilla-central/rev/b91fdb9d2883