The cloning caused comments that where added to the original node to be persisted into
the cloned node.
Espree/Acorn does not have any cloning, that's why it is working there.
This change omits comments when cloning, as removing the cloning
causes tests in babel to fail.
The primary goal of this commit is to add the ability to parse type parameter
declarations with defaults, like `type Foo<T = string> = T`. While I was in the
code, I fixed a few small things, like
* Type parameter declarations need 1 or more type parameters.
* The existential type `*` is not a valid type parameter.
* The existential type `*` is a primary type
* The param list for type parameter declarations now consists of
`TypeParameter` nodes
This fixes an issue that comments were added as leading comments
to expressions, which are not immediately folowing the comment.
This was also reported and fixed in espree, and is basically a port to
babylon. eslint/espree#256
this also fixes an issue in babel-eslint with certain rules babel/babel-eslint#289
The fix includes creating a new method on the parser called `parseArrow`.
This new function by default only checks if current position matches an
arrow. If it does returns the `node` otherwise `undefined`.
The flow plugin can then extend this function and correctly parse the typeAnnotation
and add it to the node.
With this change, in the flow plugin there is no need anymore to extend
`parseParenAndDistinguishExpression` and the arrow handling in `parseParenItem`
could also be removed, because it is all handled now in `parseArrow`.
Some existing tests were failing, because `extra->parentesized` is now missing,
but this is correct as it is now inline with parsing without flow annotation. No extra
is added for arrow function without type annotations.
In the expression-parser `this.next()` was replaced by a more specific
`this.expect(tt.parenL)`.
This syntax allows you to specify whether a type variable can appear in
a covariant or contravariant position, and is super useful for, say,
Promise.
Right now this is hacked in jankily, but in the next major release we
should stop using Identifier nodes for type parameters.
An interface export is just like a type export. In fact, it's a syntax affordance which makes the following equivalent:
```javascript
interface I_ { ... }
export type I = I_;
```
```javascript
export interface I { ... }
```
See facebook/flow#1145
This has been a feature in Flow for a long time (couldn't easily find a
specific commit adding this). Interfaces are basically undocumented, though, so
it's easy to see how this was missed.
