Follow-up on Decorators PR

[peey]

Q	A
Bug fix?	yes
Breaking change?	no
New feature?	no
Deprecations?	no
Spec compliancy?	yes
Tests added/pass?	yes
Fixed tickets	#524, #14
License	MIT

1. commit 1 Add a more helpful error message for when @dec export class {} is encountered, suggesting the user to use export @dec class {} instead (only happens in the new decorators2 plugin). As requested by @hzoo
2. commit 2 Fixes Multiple Decorators with Class as Key #524 by using a stack of decorators to allow nesting instead of using one global list of decorators. Earlier the following code would have attached both @outer and @inner to Foo but now it works correctly

   @outer(@inner class Foo {})
   class Bar {}

3. commit 3 adds the only useful test case I found in fixes #13: limit decorator use to CallExpression and IdentifierReference #14. Rest of tests are either already present or refer to an outdated version of the spec. It can now be closed.

[existentialism]

👍

[existentialism]

Nit, might read a little better as:

Using the export keyword between a decorator and a class is not allowed. Please use export @dec class instead"

[peey]

Yep, I think that's better too. Will make changes and push it

[bakkot]

I'd combine this with the above clause, personally -

if (this.match(tt._export)) {
  if (allowExport) {
    return;
  }
  this.raise(this.state.start, "Using the export keyword between a decorator and a class is not allowed. Please use `export @dec class` instead");
}

[bakkot]

I'd clarify here that foo applies only to the second class and bar only to the first.

[bakkot]

Haven't checked over all the output carefully, especially the source locations, but otherwise LGTM.

[peey]

@hzoo do note that this isn't as big a change as the previous PR was so it wouldn't need as many reviews (in fact we could do with 2-3 reviews just like for any standard bugfix PR).

[hzoo]

Yeah I don't think we need all the reviews just pinging people anyway 👍